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Soil Block Saga

Omaha, NE(Zone 5b)

I promised, in, to document using soil blocks this year instead of so much plastic.

So . . . here it begins.

1. Sifting

I don't have a lot of time today, but I want to get my seeds started by the weekend.

For making the micro-blocks (which are approximately 3/4-inch cubes), it's recommended that the mix be sifted through a 1/4-inch screen. This is to remove any pieces of material large enough to keep the little blocks from compacting properly. (If they don't compress correctly, it seems that they'll more easily fall apart.) Fortunately, I have both 1/4-inch and 1/2-inch sieves for my soil sifter.

It's a nice day, the warmest we've had so far this year (76 degrees at 4:21 PM), but it's windy--10 to 15 mph from the south, gusting to 30. The potting shed is 75 feet west and hasn't been made ready for the season yet, so I set up a "sifting station" up close to the southwest corner of the house. The garage helps break the wind.

I want 900 of those little blocks. The math says that, allowing for compacting by 2-1/2 to 3 times, I'll need between 1/2 to 2/3 cubic foot of mix. Since the unused stuff can always go back in the bag, I'll go for about a cubic foot. If I fill one of the green tubs about 7 to 8 inches deep, that should be enough.

Sifting takes less time than setting up to do it. I use the plastic coffee container as a scoop.

The Pro-Mix has a very fine texture. The only thing left behind on the screen are clumps, soft little clods up to about an inch in diameter, and they break up easily into very fine mix, but it's faster just to shake the sifter and dump the clods in the other tub before returning them to the bag. With this mix, at least, the sifting step can probably be skipped.


Adding water and playing in the mud to make the micro-blocks!

This message was edited Apr 21, 2010 7:28 PM

Thumbnail by RussMartin4154
Omaha, NE(Zone 5b)

"Houston, we've had a problem"

I thought I'd be playing in the mud today, making oodles of micro-blocks, but . . . where the heck am I going to put them? Diagnosis: Cart before the horse.

2. Preparing some trays for micro-blocks

I want gentle heat for germination, the ability to bottom-water, and to use my Perma-Nest trays.

Putting a Perma-Nest tray on top of a Hydrofarm heat mat doesn't work. I tried it in my shop: The long "ribs" and six "feet" on the bottom of the tray raise most of its bottom surface 1/4 inch above the mat, largely defeating the mat's purpose. Aha!--I'll put the mat inside the tray! But what about water? The Hydrofarm web site says the mats are "waterproof", but the mats themselves are imprinted with dire warnings: "Place the mat on a well drained surface (without standing water)"; "Do not place mat inside tray or cover directly with soil or growing medium. . . . DO NOT IMMERSE IN WATER."

A call to Hydrofarm technical support doesn't help much. Yes, I'm told, the mats are "waterproof", meaning you can spill water on them and it won't hurt them. (C'mon, guys, there is a difference between "waterproof" and "water-resistant".) I don't have time to test "waterproof-ness", but I have plenty of mats, so what the heck.

First, I arranged the mat's cord so it wouldn't lift or shift the mat. A relief loop and duct tape on the bottom of the tray accomplish this. (I believe that even the Titanic could have been saved if they'd had duct tape.) Then I slipped the heat mat into a thin plastic bag and folded the excess bag over and tucked it under.

Then I added a 3/8-inch layer of clean, fine sand, about 5 cups for each tray. The sand should make the heat distribution more even and allow water to move through the interstices to be wicked up by the blocks.

Three prepared trays (named "X", "Y", and "Z") are on the garage workbench with the heat mats plugged in. I'll check them periodically, measure the temperature, and even add some water.

With luck, tomorrow I'll start making the blocks.

(Yes, 900 micro-blocks will fit in three trays, with some room to spare at the water/relief loop end of each.)

Thumbnail by RussMartin4154
Brooksville, FL(Zone 9a)


I'm kinda with ya on your thinking of the heat mat being underneath.... but oh so worried.... I hope these won't be in your house just in case......

Looking forward to hearing how it goes with making the 900. so if you water in bottom what will keep the blocks from crumbling..?


Omaha, NE(Zone 5b)

Quote from meadowyck :
I hope these won't be in your house just in case. . . . so if you water in bottom what will keep the blocks from crumbling..?

Not to worry, Janet; they're in the garage for testing. Seed-starting got kicked out of the guest room after last year, so it's the garage and my portable greenhouse.

The most common way to water micro-blocks appears to be by misting. With the growing medium so highly compressed, I don't think they can crumble if they don't dry out--at least, that's what I've read and been told. But this is also a good trial run before bottom-watering the 2-inch blocks I'll be using next.

This message was edited Apr 5, 2010 3:24 PM

Brooksville, FL(Zone 9a)

Will be watching with a lot of interest and hope all trials go well for you.


Omaha, NE(Zone 5b)

Don't you hate it when work interferes with your hobbies?

Once again, I expected to make my micro-blocks today . . . but a client had a technical emergency, so there went most of the day. It's been said, "Life is what happens while you're making other plans."

It's not an entire loss, though. In fact, I'll take advantage of it.

2a. Testing the heat mats in the trays

As of when the photograph was made, the heat mats in all three prepared trays have been running for about 28 hours. The sand is palpably warmer to the touch and is now nicely dry. It feels as if it will provide a good pediment for the blocks. The mats are intended to keep the temperature about 10 to 20 degrees above ambient.

But . . . it was warm (high 70s) yesterday and warmer (low 80s) today. It's supposed to be a lot cooler tomorrow (mid 50s). I'll go ahead and let everything run until tomorrow afternoon and measure the dry sand temperatures two or three times after this evening.

Update, April 2

It's not quite noon. Outside, it's 57 degrees and trying to rain. It's 60 in the garage. The sandy surface in the trays measures anywhere from 79 to 83 degrees.

This message was edited Apr 2, 2010 11:34 AM

Thumbnail by RussMartin4154
Brooksville, FL(Zone 9a)

looking forward to reading about your trials.....


Omaha, NE(Zone 5b)

For early April, it's a nice March day: Partly cloudy, breezy (ENE 8 mph, gusting to 28), mid 60s, about 0.04 inch of rain this morning. But the forecast is for lows in the mid 30s for the next couple nights.

Playing in the mud (or playing in the wet soilless medium, which doesn't sound as fun) . . .

3. Making micro-blocks

As you see in the photograph, I put everything on a large, black plastic tray that once was part of a dog kennel (crate). I save odd things . . .

There's the big green tub of sifted mix from 1 above, some plastic bags, 2-quart measure graduated in half-cups, small pink washpan (probably from a hospital visit), one-pound loaf pan filled with water, large tweezers, wooden spoon, the blocker (red trim), a scraper (actually the bottom from the kitchen box grater--you could use a 4- or 6-inch scraper from the hardware store), and a prepared tray.

In that partly-filled tray, along with 200 blocks, there is also one lone block next to a shiny new penny for scale.

First, I must wet the mix. The consistency recommended is of "cooked oatmeal" or of "peanut butter", which to me don't seem the same. But I'll not take time out to make oatmeal, nor shall I reach into the peanut butter jar, be it smooth or chunky.

I start with 3 quarts (12 cups) of mix and, mostly by guess, add 1 quart (4 cups) of warm water, then mix it with the spoon. A suggested test is squeezing a handful of wet mix to see if the resulting clod holds its shape. It does, but it seems to fall apart easily, so I add another cup of water, bringing the water up to 5 cups. This sticks together and, in my hand, "feels" about right.

In some articles, the wet mix is called "slurry"; in others, just "slur". Since I know the difference between the nouns slurry and slur, I'll go with slurry. Civil engineers, mining engineers, and petroleum engineers will likely agree.

I try the blocker. Press, press, press into the slurry, each time in a different place (watching to see that water is squeezed out of the top of the blocker's cells), scrape the bottom of the blocker, then eject the blocks. Hey, not bad--nifty, even! I rinse the blocker in the loaf pan and do a couple more. It seems to work best if the slurry is 3 or 4 times the depth of the blocker's sides.

But sometimes blocks are missing! I look in the pan of slurry and, sure enough, a few get left behind, stuck in place when the blocker is lifted out. Solution: After each press, turn (rotate) the blocker slightly (just a few degrees) before lifting--no more "lost" blocks.

The sand in the trays has dried out as a result of testing the trays with the heat mats. Since I don't want dry sand sucking the moisture back out of the blocks, I moisten the sand.

So the procedure is: (1) press, twist, and lift three times to load or "charge" the blocker; (2) scrape the bottom of the blocker; (3) eject the blocks; (4) rinse the blocker and scraper; (5) level the slurry; and repeat as necessary, 20 cute little "blocklets" at a time. This is both faster and easier than it sounds.

The first batch of slurry makes 240 blocks. By a happy coincidence, the loaf pan, three-fourths filled, holds the next 5 cups of ("dirty") water.

Because of the water squeezed out and left behind each time the blocker is charged, each successive batch of slurry mixed is a bit wetter, so at some point, successive batches can begin to be made with only 4 cups of water.

Since I won't be sowing the blocks until tomorrow at the soonest, I keep them from drying out by slipping each entire tray into a plastic bag and taping the end.

From start to finish--collecting all the implements, setting up, experimenting, making 900 blocks, taking notes and photographs, then cleaning up--less than 3 hours, and that included two cigarette breaks.

Side note 1: There is something off, either with my math or my assumptions or the information I was given: I used only about 0.4 cubic foot of the dry, sifted mix, not even the half-cubic-foot minimum I expected. I'll consider this and report back.

Side note 2: Although the blocks seem for now to hold together adequately, I think the mix might benefit from a fractional addition of some kind of longer fiber--perhaps coir?

This message was edited Apr 6, 2010 5:12 PM

Thumbnail by RussMartin4154
Omaha, NE(Zone 5b)

Addressing side note 1:

(You can skip this part without missing much.)

Okay, let's review the math.

One block is about 0.675 inch square at the base, 0.635 inch square at the top, and 0.750 inches tall, so it's not a perfect cube. The cross-section is a trapezoid. It will have the same volume as a shape 0.655 inch square and 0.750 inch tall. 0.655 x 0.655 x 0.750 = 0.322 cubic inch.

For 900 blocks, we'd need 900 x 0.322 = 290 cubic inches or 290 / 1728 = 0.168 cubic foot. (A cubic foot is 1728 cubic inches.)

But the mix is dry and sort of fluffy to start with. We wet it, then compress it three times, squeezing excess water out. If the compression is 2-1/2 times, we'd need 2.5 x 290 = 725 cubic inches or 725 / 1728 = 0.420 cubic foot. If the compression is 3 times, the numbers become 3 x 290 = 870 cubic inches or 870 / 1728 = 0.503 cubic foot.

By my measurement, I actually used about 713 cubic inches of dry mix, about 0.413 cubic foot. Doing the math backwards, that means 713 / 290 = 2.46 compression.

Okay, guess there was nothing wrong with the math after all. 2.46 is close enough to 2-1/2.


Material. The type of mix and how moist it already is surely will affect the compression obtained. My first experiments in the garage some weeks back were with Miracle Gro "potting mix" from Home Depot that I had laying around from last year.

Human factor. Pressing harder or not as hard on one or more of the three presses to charge the blocker will affect the apparent compression obtained.

So the most definitive thing that can be said is that a compression of 2.5 is about right for the Pro-Mix that I'm using and for my personal technique in charging the blocker. A rule-of-thumb compression of at least 3 is probably good for planning how much dry mix will be needed, even if it isn't all used, because there will be a point where there is slurry left but not enough to properly charge the blocker because the wet mixture isn't deep enough.

This message was edited Apr 5, 2010 12:42 PM

Omaha, NE(Zone 5b)

4. Labeling the seedlings

Since the micro-blocks are far too small for any conventional labeling method, a different strategy is called for: A "map" for each tray.

I'm using sheets with a primary grid (solid lines) of 3 x 5 = 15 major divisions, each of which is subdivided by a 4 x 5 = 20 secondary grid (dashed lines). 15 x 20 =300 blocks per tray. 300 x 3 trays = 900 blocks.

Working from my color-coded list, I mark off which seeds will be placed where. Mostly, I go alphabetically from front to back, then left to right. Tomatoes go first, filling 2-1/3 trays. The remaining 2/3 of the third tray is peppers (hot, then ornamental, then sweet) and one lonely octet of eggplants.

Obviously, it's important that the trays themselves be labeled and that the front of each tray be marked. Were I really compulsive, I'd label each tray at both ends, then mark "front" and "back". But I'll label just one end and that will always be "front".

I'm not starting identical numbers of all varieties because I need a few more of some, others are comparisons of the same variety's seeds from two or more vendors/trades, and, in a couple cases, I'm starting old seeds.

That took about an hour. Another cup of coffee, a cigarette, and I'll be ready to sow seeds!

Thumbnail by RussMartin4154
Brooksville, FL(Zone 9a)

and I thought I was anal about my seed planting....

I love the in depth info on how much pro mix it was going to take.... I've done that with mine as well to figure my total cost per plant. Although I will say I believe you are more analytical than I. LOL

I do see that the pressure will most certainly change the compaction of each set of cubes. You can well think you are pressing the same but you never will. That is due to be human and not machine.....

I like you color coding idea as I've only been using hang tags for what seed type in what rows.

Thanks for such great detailed info..

can you take a closer picture of the block next to the penny or just even a closer look at the group of blocks together?


Carmel, IN(Zone 5b)

WOW! Thank you for this detailed account. I've been wondering about soil blocks for some time now, and this answers a lot of my questions. Can't wait to follow your results.

Omaha, NE(Zone 5b)

Quote from meadowyck :
. . . and I thought I was anal about my seed planting . . . Can you take a closer picture of the block next to the penny or just even a closer look at the group of blocks together?


Janet, I'm an engineer. It's not just something I do, it's something I am!

And, as Robert A. Heinlein once wrote, "If it can't be expressed with mathematics, it's not fact; it's opinion."

I'll do a couple more photos tomorrow, one of a coin or coins with a single block, and one of a group of 20 blocks.


This message was edited Apr 5, 2010 3:23 PM

Omaha, NE(Zone 5b)

The plastic bag over each tray collected condensation. When I slid a tray out of its bag, everything was nice and moist and smelled wonderfully "earthy", even if no real soil was involved.

5. Sowing to the blocks

In the photograph, you see the work station set up in the garage. It's close to the prepared trays. That way, I didn't have to schlep them down and up the basement stairs. (I was certain that I couldn't get away with using the dining table as I did for 4 above!)

In the background, you see trays Y and Z, still in their moisture-retaining plastic-bag "tents", as well as a hand-pumped spray bottle that I've used only for misting. (I have a different setup for spraying.)

On the table in the foreground, I'm almost halfway through the first tray, X. Tools are: Small, shallow, white, opaque dish so I can see the seeds easily; Landware Pro-Seeder (the thing with the green bulb); seed packet; lamp; stapler and transparent tape for re-closing packets and re-attaching them to their information sheets; the "map" for the tray from 4 above; mechanical pencil; pocketknife (used as staple remover, seed envelope opener, and for emergency seed retrieval); and the soil sieve, used as the "in" basket for the seeds before they're sown. (The "out" box, for after, is out of the photograph on a shelf on the right.)

Following the chart, I work from bottom to top, first on the left four columns, then the middle four, then the right four. As I do, I add notes to the chart given vendor/source and a tick mark to show that I've finished a given variety.

The two little objects on the right and front edges of the tray are common binder clips, available at any office supply. I move them to help me keep track of where I am in the tray, in case I'm interrupted (which happened several times).

The Landware Pro-Seeder is one of the best little gadgets I've encountered. Learning to use it takes only a few minutes of hands-on practice. More about it here:
It's very similar to an expensive little tool in my shop that I use for picking up and placing tiny surface-mount electronic parts.

Using the largest tip (0.5 millimeter), I squeeze the bulb, touch the tip to a seed, and partially release the bulb. The seed is sucked up against the tip. Hold the seed over the dimple in a micro-block, squeeze a little, and the seed drops right into place. The seed needs to be dry, though, and once it is dropped onto a block, the moisture on the surface of the block holds it, so picking the seed back up with the device is harder. But for seed removal and relocation, the point of a pocketknife blade is easier and faster. A small spatulate tweezers might be even better.

Excluding interruptions, it took me 4 hours 15 minutes to sow 700 tomato seeds, 192 pepper seeds, and 8 eggplant seeds. That averages to 17 seconds per seed, which seems (and is) ridiculous, but a large part of the time was spent (1) removing the seed packet from the file sheet, (2) opening the packet, (3) putting unused seeds back in the packet, (4) sealing the packet, and (5) stapling it back onto its file sheet. What this suggests is that I need a different and better kind of seed filing system, but I'll work on that later.

The actual average time needed just to pick up a seed and put it on a block was less than 3 seconds, so I actually spent only about 45 minutes--approximately 17 percent of the total time--placing the seeds; the rest was handling the packets and paper.

After I finished a tray, I misted it thorougly. When all three were seeded, each was misted again. The heat mats were plugged in, a plastic bag supported by meter sticks was draped over them. (Before the month is out, I'll order some humidity domes for the Perma-Nest trays to use next year.) A1500-watt heater was placed on the floor to keep the temperature in the garage above 60 degrees.

Typically, micro-blocks are watered three times daily by misting. To start, I'll do that, but I'll also begin adding water to the tray and see how well the sand contributes to bottom watering.

What's next?

I can't rest too much nor admire my work for too long. I'll need to pot up (actually, to "block up") in not many days, so I must start preparing the 2-inch blocks--576 of them (16 trays of 36 blocks each).

By odd coincidence, it was also on 03 April last year that I started seeds.

This message was edited Apr 6, 2010 5:17 PM

Thumbnail by RussMartin4154
Tonasket, WA(Zone 5a)

Russ very well written and explained. Will be watching to see your seed family as they germinate and grow. thanks for all the info and pictures.


Brooksville, FL(Zone 9a)


the way to cut down paper, seed packet time is to plant all of the seeds in the packet.....teee heeee

Great job, nice detail as always.


Omaha, NE(Zone 5b)

Quote from meadowyck :
. . . can you take a closer picture of the block next to the penny or just even a closer look at the group of blocks together?


For Janet and others interested:

3a. Here, in close-up view looking down, is a 4 by 5 group of micro-blocks (20) straight from the blocker and a single block, with both penny and inch rule for scale.

This message was edited Apr 5, 2010 3:23 PM

Thumbnail by RussMartin4154
Omaha, NE(Zone 5b)

Since I had the camera and the camera stand out anyway:

5a. This is a close look down at the front right corner of tray X about 48 hours after tomato seeds were sown to the micro-blocks.

Note: As I set the 20-block groups in the trays, I staggered them left and right by rows. This was intentional for two reasons: First, to make it easier to see where I was sowing in the tray compared to the chart and, second, to provide additional clearance near the top right corner of the tray where the heat mat joins its power cord. It's a somewhat bulky interface and can't easily be covered by the uniform layer of sand; best (and easy) to avoid it.

This message was edited Apr 5, 2010 2:37 PM

Thumbnail by RussMartin4154
Brooksville, FL(Zone 9a)

great shots, oh my goodness no bigger a penny, and from the second picture I see that the seeds are just laying on top.... is that how you planted the others as well...

I'm thinking I guess you can't push the seeds in or the block would crumble???

This is very interesting and I hope you will keep us posted as they start to germinate as well as when you start to transplant them? what will you be transplanting them into?

sorry for all the questions but this is very interesting thread.


Omaha, NE(Zone 5b)

. . . and as long as the camera is handy:

5b. This is the "seed starting station", a temporary set-up to be sure.

Three scraps of 1x2 hold the plastic off of the trays so it doesn't sag under the weight of condensation and lay on the blocks. Two scraps of 2x2 hold the plastic in place. It's lifted at both ends of each tray to provide relief for air circulation.

The small, black device with red numbers showing is the thermostat control for the heat mats. Although it controls all three mats, it is sensing the temperature in the sand only in the front right corner of tray Y. That's not the best place to measure it and reading only one tray isn't ideal; from an engineering standpoint, both conditions offend me. I'll deal with that later.

Meanwhile, I've ordered some humidity domes that fit Perma-Nest trays--not the twice-as-expensive tall ones with sliding vents, just the regular ones. They will need to be modified: Ventilation holes, rear relief for the heat mat's power cord, and front relief for the cord to the temperature sensor. They should arrive in three days.

Observation: If the condensation collecting on the underside of the plastic bags is a reliable indicator, I'll not have mist the trays very often. The blocks and sand are staying nicely moist without interference by me.

Thumbnail by RussMartin4154
Brooksville, FL(Zone 9a)



Omaha, NE(Zone 5b)

Quote from meadowyck :
. . . sorry for all the questions . . .


Janet, I'm glad for your questions; they identify things you and other people want to know. Since I intend to compile all of my posts into one reference document at the end of the experiment, it should include as much relevant information as possible.

. . . from the second picture I see that the seeds are just laying on top. Is that how you planted the others as well?

Yes, I put all of them on top, in the shallow, depressed "dimples" left by the built-in dibbles in the blocker. Since both the blocks and the air are moist, it's really not much different than laying seeds on a moist paper towel inside a plastic sandwich bag.

. . . I guess you can't push the seeds in or the block would crumble?

No, I was able to press a seed into a block with the tip of the seeding tool, and the block did not crumble or collapse. I'm not convinced that inserting the seed into the mix is essential, but we'll know for sure in another day or two. I also could have sprinkled a little dry mix over them, but I'm seeking to eliminate rather than create unnecessary steps.

I hope you will keep us posted as they start to germinate as well as when you start to transplant them. What will you be transplanting them into?

I intend to document this entire adventure, all the way through placing the seedlings into the garden or into containers, because I'll be transplanting them into 2x2 soil blocks. The blocker(s) for those have optional cube-shaped dibbles that create the right-sized space into which micro-blocks can be placed, as shown in the photo (very small; not one of mine).

This message was edited Apr 5, 2010 10:30 PM

Thumbnail by RussMartin4154
Brooksville, FL(Zone 9a)

I see said the blind woman to the deaf man.....

I was just wondering how that blocks were going to fit into another, never thought about the larger block having a hole that the smaller one fit into.... so when they arrive at that stage is there another larger block that they go into or is that when they will be transplanted into the garden or a container?


Carmel, IN(Zone 5b)

Wow--this is amazing. Russ, thank you for your detailed documentation; this is a process I knew very little about, but thought it had great potential. I'm so excited you're sharing your results with us.

I have a couple of questions, but I'm going to go back and re-read everything first to make sure you haven't already answered them somewhere.

Omaha, NE(Zone 5b)

Quote from meadowyck :
. . . so when they arrive at that stage is there another larger block that they go into or is that when they will be transplanted into the garden or a container?


There is yet a larger block, a 4-inch block, that a 2-inch block can go into. The 4-inch block, properly compressed, is said to contain much more planting medium (three to four times more!) than a 6-inch diameter round pot. See the photo (again small, not very good, and not mine).

So . . . let's check out that claim, with measurements and more math:

I measured a sample each of two different 6-inch plastic nursery pots I have. Measuring to the fill line, one has a volume of 39.5 cubic inches; the other, 41.9 cubic inches. The 4-inch blocker is 4.1 inches square at the base, 3.5 inches at the top, and 4 inches high, giving a volume of 58.1 cubic inches. With compression of 2.5, this yields 145 cubic inches of mix in a 4-inch block (including the volume of the 2-inch block).

I also measured one of the 3-inch square plastic pots that I used over 300 of last year. The volume to the fill line is 25.2 cubic inches. The 2-inch blocks actually measure 1.8 by 1.9 inches at the base and top and are 1.7 inches high, giving a volume of 5.8 cubic inches; when compressed 2.5 times, this yields 14.5 cubic inches. Yes, less than the 3-inch pot, but the block takes up only 44 percent of the surface space. Put another way, in the same space occupied by 100 of those plastic pots, I can have over twice as many plants in blocks.

But I'll not be using the 4-inch blocker except to try it and demonstrate the results, because the 2-inch blocks should provide ample growing space for the maximum 6 or 7 weeks after blocking up the seedlings. (We'll know for sure in about 9 weeks.) That's all the time I expect to need before the young plants find homes in either my containers and garden or those of adoptive gardeners.

This message was edited Apr 12, 2011 1:51 PM

Thumbnail by RussMartin4154
Hutto, TX(Zone 8b)


So why not just start with 2-inch blocks? Is there anything that won't be transplanted from the 3/4" blocks? At this point, the only reason I see for using the tiny blocks is to put as many blocks as possible on the heat mats for initial germination. Is that the case?

I know that this is the tomato forum, but do you know or suspect that the blocks would be useful for starting & transplanting typically direct-sown seeds (like corn, beans, peas, squash, etc.)? It would eliminate over-sowing and thinning if the tiny blocks were used to start seeds, then quickly plant once they had germinated. It would be easy to space correctly from the initial planting.


Omaha, NE(Zone 5b)

Quote from dreaves :
So why not just start with 2-inch blocks? Is there anything that won't be transplanted from the 3/4" blocks? At this point, the only reason I see for using the tiny blocks is to put as many blocks as possible on the heat mats for initial germination. Is that the case?


David, that's an excellent question; I'm glad you asked! There are probably more answers than I can think of, offhand. I'll present my opinions based on received information and my own empirical data.

(Everyone reading this thread, please remember, I'm not a soil block maven, truly. But surely, before long--if not already--someone is going to wonder if I'm a Ladbrooke stockholder or if I'm retailing the blockers myself, or at least a shill for another retailer. I'll short-circuit that: The answer in all instances is, emphatically, "No!"--hey, folks, I'm just an engineer who's also a gardener; I'm learning as I go. Think of it as a grown-up equivalent of a school science fair project!)

Permit me first to digress: The same company (Ladbrooke, in England) also offers two blockers that make 1-1/2 inch soil blocks (either 5 or 20 at a time), but these can't be used with the 3/4-inch cubic dibbles because the remaining 3/8-inch wall is too thin; it would collapse at a mean look. Ladbrooke also makes another blocker that produces larger (about 2-1/2 by 3 inch) blocks, but those aren't compatible with "blocking up" to the 4-inch blocker.

If you wanted to skip the 3/4-inch blocks, the best choice--depending on the plant to be started--might be the 1-1/2 inch blocks.

That aside, I'm starting 900 seeds (700 tomato, 192 pepper, and 8 eggplant) in 3 trays and less than 6 square feet of space. To do so with 2x2 blocks, I'd need 25 square feet, over four times as much, and to do it with 2x2 blocks in 12x23 Perma-Nest trays, I'd need almost 50 square feet, not to mention 25 trays.

With 100 percent germination, sowing directly to the 2x2 blocks would be ideal--but I can't expect 100 percent germination on all of 70 different tomatoes, 23 different peppers, and 1 eggplant, from a cumulative 20 different sources. It's certain that some of those 3/4-inch blocks will be nulls. Any unproductive block will have to be discarded.

For discussion, let's assume 75 percent germination. In that instance, I'd end up tossing 25 percent of the blocks. I'll certainly prefer to give up 238 cubic inches (about 1/8 cubic foot) of plain mix than 4500 cubic inches (just over 2-1/2 cubic feet) of expensively augmented mix.

. . . do you know or suspect that the blocks would be useful for starting & transplanting typically direct-sown seeds (like corn, beans, peas, squash, etc.)? It would eliminate over-sowing and thinning if the tiny blocks were used to start seeds, then quickly plant once they had germinated. It would be easy to space correctly from the initial planting.

Suspect, yes; but, being an empiricist, I don't know it yet. Large seeds like those you mention almost certainly require the large(r) block. I'm not just a tomatohead; I'll try some beans, squash, and cucumbers after this experiment is finished. I'd also like to play with greens and herbs--things that have really tiny seeds (like Osaka Purple Mustard).

The elegance I see in using soil blocks, aside from eliminating unnecessary handling ("therbligs") and materials, is versatility. In engineering terms, the soil block approach is both horizontally and vertically integrated.

This message was edited Apr 6, 2010 5:24 PM

Westbrook, CT(Zone 6a)

Russ, you are giving us a very useful and informative discussion of soil blocking; thanks for your hard work and dedication.

I have one question about moving the small blocks to the larger one. Does this count as transplanting, since the entire root and its surrounding soil is moved together and would not disturb the roots as much as regular transplanting? Our famous and beloved Dr. Carolyn says:
          "OK, why is it so important to transplant? Because it shocks the plant and
          retards foliage growth so that root growth can occur. If you don't do it you
          get huge leggy stupid seedlings that flop all over the place and are a
          disgrace to the genus Lycopersicon. That's why. LOL "

I have been starting my tomato seeds in those shallow 20-row trays which only have about a half-inch depth, yet when I tease the seedlings out to transplant them, the roots are often much longer than this. I then put them in 1.5 inch holes poked into 2" (or more) deep pots to sink them up to their leaves so the stem can grow more roots. It would seem that the 3/4 inch depressions the block makers put in your 2 inch blocks would not allow this. Is there any way to make deeper impressions in your larger blocks, since many experts advise setting the transplants deeper?

Brooksville, FL(Zone 9a)

I like your thinking here in your question about the transplanting now allowing for the new seedling to be buried up to its leafs.

Unless by the time it goes into the second block and has it 2nd set of leafs (the true ones) it would be time to transplant to a pot or the garden.

By the way Russ, I don't recall you saying what you are going to do with all of those plants?


Omaha, NE(Zone 5b)

Quote from DonShirer :
Does this count as transplanting, since the entire root and its surrounding soil is moved together and would not disturb the roots as much as regular transplanting? . . . It would seem that the 3/4 inch depressions the block makers put in your 2 inch blocks would not allow [planting seedlings up to their leaves]. Is there any way to make deeper impressions in your larger blocks, since many experts advise setting the transplants deeper?[/quote]
Two good questions, Don. I'm not sure that I am yet qualified to give even an opinion, much less provide a competent answer from my own knowledge or experience.

I'll defer to David Tresemer and his booklet, Transplants in Soil Blocks, a relevant excerpt from which is attached. According to him, yes, blocking up counts as transplanting; and, no, the plants thus transplanted do not suffer root insult ("shock"). In fact, avoiding the shock is stated as a benefit of using soil blocks.

This discussion may provide some food for thought:

Apparent to me is this: I need to run an A-B test, with a 72-cell flat and the 3-inch pots (I have plenty left over from last year) as control for comparison, to see which method produces those "huge leggy stupid seedlings".

Ladbrooke does not offer anything to create a deeper space. From a physical standpoint, it appears that it would not be difficult. I could certainly fashion something from wood, or even cast something with acrylic resin. I'll put that on the "future projects" list.

[quote="meadowyck"]By the way Russ, I don't recall you saying what you are going to do with all of those plants.

Janet, some go to my garden (of course!), and rather a lot go to people who've requested I start plants for them. The remainder will be offered at the Benson Farmers Market. Those still unsold on June 5 will on June 6 be donated to parishioners at St. Benedict the Moor Catholic Church.

This message was edited Apr 6, 2010 5:32 PM

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Omaha, NE(Zone 5b)

1.4 inches of rain in the wee hours this morning.

Okay, it's time for a little more arithmetic.

6a. Planning for the 2-inch blocks

I intend 4 x 9 = 36 of these blocks per tray and a total of 16 trays. 36 x 16 = 572 blocks.

Each tray gets a 5-cup sand pediment, so that's 5 x 16 = 80 cups. That's really not much; 80 cups / 119.7 cups per cubic foot = 0.67, about 2/3 cubic foot.

The blocks aren't exact 2-inch cubes; they are in fact 1.8 by 1.9 inches at both base and top and 1.7 inches high. 1.7 x 1.8 x 1.9 = 5.8 cubic inches. Using the compression factor of 2.5, I'll need 5.8 x 2.5 x 572 = 8294 cubic inches of mix. That's 8294 / 1728 = 4.8 cubic feet.

To simplify things, I'll just call it 5 cubic feet.

For these blocks, I'm going to try a blend of 8 parts Pro-Mix, 1 part 100% vegetable compost, and 1 part worm castings. That translates to 4 cubic feet of Pro-Mix and 1/2 cubic foot each of the compost and the worm castings.

The compost may need to be sifted with the 1/4-inch sieve.

We're expecting rain after midnight and into tomorrow morning, so mixing the growing medium will wait at least until tomorrow afternoon, possibly even until Thursday.

This message was edited Apr 7, 2010 5:13 PM

Omaha, NE(Zone 5b)

0.20 inch more rain this morning.

Yes, we have germination!

This is the upper left part of tray X (rotated left 90 degrees) at 4 days. The red ellipse shows what happens when an extra seed is dropped between blocks and not retrieved.

Quote from On April 5, I :
I'm not convinced that inserting the seed into the mix is essential, but we'll know for sure in another day or two. I also could have sprinkled a little dry mix over them, but I'm seeking to eliminate rather than create unnecessary steps.

One thing I see: For at least a few seeds, as the radicle makes its way out of the seed coat to become a root, it can actually push the seed to the edge of the block, and even over the edge to fall in between blocks.

I'm able to rescue the few that do this, but I now think that the small extra step of pressing the seed into the block, perhaps with an orangewood stick, would be a good idea. I also observed that, in a few cases, the little root grows across the surface of the top and down the side.

This message was edited Apr 7, 2010 9:23 PM

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Omaha, NE(Zone 5b)

Small changes:

The boards weren't doing the best job of holding the pastic up, especially when it became weighted with condensation.

I reduced the number of boards to 2 and secured the plastic in place with binder clips. I'm looking forward to having the plastic domes, which should arrive tomorrow.

Update on domes, April 9: Well, they aren't arriving Thursday, or even Friday, after all. Although promised to ship on April 6, they didn't ship until April 8. By the time they get here (April 13, according to the tracking information), I won't need them for the tomatoes, only the fewer peppers. Sigh.

While the heat mats are obviously working, the distribution of the heat seems both uneven and generally poor. Then it occurred to me that the same problem that impedes using the heat mats under Perma-Nest trays might bear on this problem, too: The ribs and feet on the tray bottoms raise the trays and allow air circulation beneath them, carrying off at least some useful heat.

The first attempted remedy: A length of glass wool insulation beneath the trays.

I also moved the temperature sensor from the right front corner of tray Y to the middle of the right side. Using an electronically-compensated K-type bead thermocouple, I measured the temperature in a few blocks and at different points in the sand pediment.

This message was edited Apr 9, 2010 7:22 PM

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Carmel, IN(Zone 5b)

Russ: Just a thought on the heat issue--I recently purchased a heat mat/seedling tray unit at a local big box store. The heat mat sits inside of the outer tray (neat little opening just large enough to run cord through); flat with cell-packs sits on top of heat mat with clear plastic dome. Any possibility you can find a shallow container just slightly larger than your Permanest trays to recreate something similar? This particular heat mat set-up has really performed better than my heat mats sitting on my shelf with trays on top; I'm sure it's because the heat is not getting lost into the atmosphere.

Brooksville, FL(Zone 9a)


I have several survives that fell between my pellets and after they germinated I just planted them... I love that tool you have for the tiny seeds, I have always seen it but didn't know if it would really work.


that is a great observation about the heat being lost when on the shelves.

I'm going tomorrow night when I get home from work, find something to put my heat mat in then the tray on top to see if I can get faster germination.

I've only got a month before our garden club plant sale, and I've got to get seeds going big time... so If I can get germination with a few days then they can come off and the new ones on.

thanks so much for posting your observation.


Omaha, NE(Zone 5b)

What a great day! Sunny, low 70s, light breeze.

From setting up to cleaning up including the obligatory photos and note-taking, what follows takes about 3 hours.

6b. Mixing the medium

I'm still suspicious of the compression factor, since I worked by volume last time, so I'm going to make a little extra: 5-3/4 cubic feet (allowing for x3 compression) instead of just 5 cubic feet. This time, I'm going to calculate by weight rather than volume because I'm dealing with three different things: Pro-Mix, vegetable compost, and worm castings.

Weighing will be done with the humble bathroom scale seen just in front of the Pro-Mix bags. I check the scale by weighing 6 pounds of peanut butter; it's close enough.

This particular Pro-Mix weighs 14.3 pounds per cubic foot. The vegetable compost is 30 pounds per cubic foot; the worm castings, 40 pounds per cubic foot. I will need about 66 pounds of Pro-Mix (4.6 cubic feet), as well as 17 pounds of compost and 23 pounds of worm castings (about 0.57 cubic feet each). 4.6 + 0.57 + 0.57 = 5.74 cubic feet. And I'll need something in which to mix all of this--a child's wading pool should do nicely.

The compost is nice and fine, but with occasional small twigs and pieces of bark. I try sifting it with the 1/4-inch sieve, which proves largely ineffective; the twigs and bark pieces simply go through the screen endwise. Okay, I'll skip the rest of the sifting and keep my fingers crossed.

Everything is mixed together by stirring with a hoe, turning with a shovel, and repeating the process until I'm bored with it. But it looks and feels nicely homogeneous and smells wonderful.

This message was edited Apr 9, 2010 7:24 PM

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Omaha, NE(Zone 5b)

6c. Making 2-inch blocks

I don't want to wet the whole 5-3/4 cubic feet of medium at the same time, so I'll use the wheelbarrow.

3:1 of mix to water was a good starting point for making micro-blocks, so I'll start with that but on a larger scale: 15 measures of dry mix, add 5 measures of water, stir, let sit for a few minutes, then stir again and dump the slurry onto the big tray.

I try the 4-block hand blocker first. It works nicely; I make a dozen blocks, then toss them back into the slurry and test the stand-up 12-block device. Good results the first time out. I make another two dozen and throw them back. I think I'll use the stand-up blocker.

My technique isn't refined yet; my lack of finesse shows up about once in every three dozen blocks: For one or two blocks, a corner or side of the wall is broken.

The procedure is nearly the same as for the micro-blocks: (1) press, twist, and lift three times to load or "charge" the blocker; (2) scrape the bottom of the blocker; (3) eject the blocks; (4) rinse the blocker; (5) level the slurry (the hoe is good for doing this); and repeat as necessary,

Getting the right proportion of water is important: Too much, and the blocks slip and fall right back out of the blocker; too little and the top walls break or crumble when the blocks are ejected. With the stand-up blocker, learning to eject the blocks correctly is also important: Make sure the bottom is level and sitting on the surface receiving the blocks, then eject, release, eject again and, while holding the handle down, lift the blocker away from the blocks.

Once I got used to the feel and rhythm of the process, the only damage to the walls of the blocks occurred if I failed to rinse the blocker.

After each Perma-Nest tray is filled with 36 blocks (three sets of 12), I slip it into one of those ubiquitous plastic bags and set it in the rack.

Next: "Blocking up" the seedlings. None have the first true leaves yet, so it may be another day or three.

This message was edited Apr 9, 2010 7:20 PM

Thumbnail by RussMartin4154
Omaha, NE(Zone 5b)

This is my third tray of 2-inch blocks.

Thumbnail by RussMartin4154
Omaha, NE(Zone 5b)

. . . and I promised everyone I'd make at least one 4-inch block, just for show. Here it is, with a 2-inch block and a 6-inch rule for comparison.

Thumbnail by RussMartin4154
Omaha, NE(Zone 5b)

10 days since the last post; it's time to bring things up to date.

You've heard of The Ides of March? The next installment begins with The Ides of April (also known as "Income Tax Day"):

7. "Blocking up" the seedlings

Seeds started on 03 April are definitely seedlings on 15 April.

12 days is probably too long for the micro-blocks. Despite the only light being a 60-watt CFL in the ceiling several feet away, the seedlings are gangly. A few even are floppy. There is no sign yet, of course, of any true leaves. (They barely start to appear in about 3 more days.) I may have left the heat mats on too long.

During that period, I needed to mist the seedlings lightly only every second day.

I'll give the peppers a couple of extra days; some have just barely germinated.

In the photo, the seedlings in Tray X have been "blocked up". After doing this, each tray of seedlings in large blocks was misted before being racked. But I should not have left the plastic off of Trays Y and Z; while attending to Tray X, the other two trays dried out enough that some seedlings began to droop.

This message was edited Apr 22, 2010 12:21 PM

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