Continued from here: http://davesgarden.com/forums/t/527353/
I’m amazed at the interest this thread has garnered. Since the original posting has become unwieldy for those with dial-up connections, and I was getting some pressure to repost, (smiling at that) I took the original & tried to polish it just a little. I hope it’s not so long that it gets passed over. Hopefully, we can exchange some good ideas and remain focused on the subject of container soils. Please forgive any grammer/spelling errors. It’s late, and I’m growing weary after a full day off - a good day off, spent in the garden sunshine.
As container gardeners, our first priority should be to insure the soils we use are adequately aerated for the life of the planting, or in the case of perennial material (trees, shrubs, garden perennials), from repot to repot. Soil aeration/drainage is the most important consideration in any container planting. Soil is the foundation that all container plantings are built on, and aeration is the cornerstone of that foundation. Since aeration and drainage are inversely linked to soil particle size, it makes good sense to try to find and use soils or primary components with particles larger than peat. That components retain their structure for extended periods is also extremely important. Pine and some other types of conifer bark fit the bill nicely and I’ll talk more about them later.
The following also hits pretty hard against the futility of using a drainage layer in an attempt to improve drainage. It just doesn't work. All it does is reduce the amount soil available for root colonization. A wick will remove water from the saturated layer of soil at the container bottom. It works in reverse of the self-watering pots widely being discussed on this forum now.
Since there are many questions about soils appropriate for use in containers, I'll post my basic mix later, in case any would like to try it. It will follow the Water Movement info.
Water Movement and Water Retention in Container Soils
Consider this if you will:
Soil need fill only a few needs in plant culture. Anchorage - A place for roots to extend, securing the plant and preventing it from toppling. Nutrient Sink - It must retain sufficient nutrients in available form to sustain plant systems. Gas Exchange - It must be sufficiently porous to allow air to the root system and by-product gasses to escape. And finally, Water - It must retain water enough in liquid and/or vapor form to sustain plants between waterings. Most plants could be grown without soil as long as we can provide air, nutrients, and water, (witness hydroponics). Here, I will concentrate primarily on the movement of water in soil(s).
There are two forces that cause water to move through soil - one is gravity, the other capillary action. Gravity needs little explanation, but for this writing I would like to note: Gravitational flow potential (GFP) is greater for water at the top of the container than it is for water at the bottom. I'll return to that later. Capillarity is a function of the natural forces of adhesion and cohesion. Adhesion is water's tendency to stick to solid objects like soil particles and the sides of the pot. Cohesion is the tendency for water to stick to itself. Cohesion is why we often find water in droplet form - because cohesion is at times stronger than adhesion, water’s bond to itself can be stronger than the bond to the object it might be in contact with; in this condition it forms a drop. Capillary action is in evidence when we dip a paper towel in water. The water will soak into the towel and rise several inches above the surface of the water. It will not drain back into the source. It will stop rising when the GFP equals the capillary attraction of the fibers in the paper.
There will be a naturally occurring "perched water table" (PWT) in containers when soil particulate size is under about .125 (1/8) inch.. This is water that occupies a layer of soil that is always saturated & will not drain from the portion of the pot it occupies. It can evaporate or be used by the plant, but physical forces will not allow it to drain. It is there because the capillary pull of the soil at some point will surpass the GFP; therefore, the water does not drain, it is "perched". The smaller the size of the particles in a soil, the greater the height of the PWT.
If we fill five cylinders of varying heights and diameters with the same soil mix and provide each cylinder with a drainage hole, the PWT will be exactly the same height in each container. This saturated area of the pot is where roots seldom penetrate & where root problems frequently begin due to a lack of aeration. Water and nutrient uptake are also compromised by lack of air in the root zone. Keeping in mind the fact that the PWT height is soil dependent and has nothing to do with height or shape of the container, we can draw the conclusion that: Tall growing containers will always have a higher percentage of unsaturated soil than squat containers when using the same soil mix. The reason: The level of the PWT will be the same in each container, with the taller container providing more usable, air holding soil above the PWT. Physiology dictates that plants must have oxygen at the root zone in order to maintain normal root function.
A given volume of large soil particles has less overall surface area when compared to the same volume of small particles and therefore less overall adhesive attraction to water. So, in soils with large particles, GFP more readily overcomes capillary attraction. They drain better. We all know this, but the reason, often unclear, is that the height of the PWT is lower in coarse soils than in fine soils. The key to good drainage is size and uniformity of soil particles. Mixing large particles with small is often very ineffective because the smaller particles fit between the large, increasing surface area which increases the capillary attraction and thus the water holding potential.
When we add a coarse drainage layer under our soil, it does not improve drainage. It does though, conserve on the volume of soil required to fill a pot and it makes the pot lighter. When we employ this exercise in an attempt to improve drainage, what we are actually doing is moving the level of the PWT higher in the pot. This simply reduces the volume of soil available for roots to colonize. Containers with uniform soil particle size from top of container to bottom will yield better and more uniform drainage and have a lower PWT than containers with drainage layers. The coarser the drainage layer, the more detrimental to drainage it is because water is more (for lack of a better scientific word) reluctant to make the downward transition because the capillary pull of the soil above the drainage layer is stronger than the GFP. The reason for this is there is far more surface area for water to be attracted to in the soil above the drainage layer than there is in the drainage layer, so the water “perches”.
I know this goes against what most have thought to be true, but the principle is scientifically sound, and experiments have shown it as so. Many nurserymen are now employing the pot-in-pot or the pot-in-trench method of growing to capitalize on the science.
If you discover you need to increase drainage, you can simply insert an absorbent wick into a drainage hole & allow it to extend from the saturated soil to a few inches below the bottom of the pot, or allow it to contact soil below the container where it can be absorbed. This will successfully eliminate the PWT & give your plants much more soil to grow in as well as allow more, much needed air to the roots.
Uniform size particles of fir, hemlock or pine bark are excellent as the primary component of your soils. The lignin contained in bark keeps it rigid and the rigidity provides air-holding pockets in the root zone far longer than peat or compost mixes that too quickly break down to a soup-like consistency. Conifer bark also contains suberin, a lipid sometimes referred to as nature’s preservative. Suberin is what slows the decomposition of bark-based soils. It contains highly varied hydrocarbon chains and the microorganisms that turn peat to soup have great difficulty cleaving these chains.
In simple terms: Plants that expire because of drainage problems either die of thirst because the roots have rotted and can no longer take up water, or they starve/”suffocate” because there is insufficient air at the root zone to insure normal water/nutrient uptake and root function.
To confirm the existence of the PWT and the effectiveness of using a wick to remove it, try this experiment: Fill a soft drink cup nearly full of garden soil. Add enough water to fill to the top, being sure all soil is saturated. Punch a drain hole in the bottom of the cup & allow to drain. When the drainage stops, insert a wick into the drain hole . Take note of how much additional water drains. Even touching the soil with a toothpick through the drain hole will cause substantial additional water to drain. This is water that occupied the PWT before being drained by the wick. A greatly simplified explanation of what occurs is: The wick "fools" the water into thinking the pot is deeper, so water begins to move downward seeking the "new" bottom of the pot, pulling the rest of the water in the PWT along with it. If there is interest, there are other simple and interesting experiments you can perform to confirm the existence of a PWT in container soils. I can expand later.
I remain cognizant of these physical principles whenever I build a soil. I haven’t used a commercially prepared soil in many years, preferring to build a soil or amend one of my 2 basic mixes to suits individual plantings. I use many amendments when building my soils, but the basic building process starts with conifer bark and perlite. Sphagnum peat usually plays a minor, or at least a secondary role in my container soils because it breaks down too quickly and when it does, it impedes drainage and reduces aeration.
Note that there is no sand or compost in the soils I use. Sand, though it can improve drainage in some cases, reduces aeration by filling valuable macro-pores in soils. Unless sand particle size is fairly uniform and/or larger than about ˝ BB size I leave it out of soils. Compost is too unstable for me to consider using in soils. The small amount of micronutrients it supplies can easily be delivered by one or more of a number of chemical or organic sources.
My Basic Soil
I'll give two recipes. I usually make big batches. I also frequently add agricultural sulfur to some soils for acid-lovers or to soils I use dolomitic lime in.
5 parts pine bark fines
1 part sphagnum peat (not reed or sedge peat please)
1-2 parts perlite
garden lime or gypsum
controlled release fertilizer
micronutrient powder (or other continued source of micronutrients)
3 cu ft pine bark fines (1 big bag)
5 gallons peat
5 gallons perlite
2 cups lime or gypsum (you can add more to small portion if needed)
2 cups CRF
1/2 cup micronutrient powder (or other)
3 gallons pine bark
1/2 gallon peat
1/2 gallon perlite
small handful lime or gypsum
1/4 cup CRF
1 tbsp micro-nutrient powder
I have seen advice that some highly organic (practically speaking - almost all are highly organic) container soils are productive for up to 5 years or more. I disagree and will explain why if there is interest. Even if you were to substitute fir bark for pine bark in this recipe (and this recipe will long outlast any peat based soil) you should only expect a maximum of two to three years life before a repot is in order. Usually perennials, including trees (they're perennials too, you know) ;o) should be repotted more frequently to insure vigor closer to their genetic potential. If a soil is desired that will retain structure for long periods, we need to look more to inorganic components. Some examples are crushed granite, pea stone, coarse sand (see above - no smaller than ˝ BB size in containers, please), Haydite, lava rock (pumice), Turface or Schultz soil conditioner.
I hope this starts a good exchange of ideas & opinions so we all can learn.
Container Soils: Water Movement and Retention II
Continued from here: http://davesgarden.com/forums/t/527353/
Al, thank you so much for all of your work. It is much appreciated.
Al, yes thanks for all the above info. My main problem is procuring pine fines.None available in Tonasket, and last time i checked at Wal Mart, nothing there either.I have all/use the rest of your suggestions.
Actually I have had pretty good luck using Whitney Farms potting mix. I had been using worm castings, but can't find any within my area of 150 miles.
You should be able to find either fir or redwood bark where you are, Ruth. either will work. If you're happy with the results you're getting with your mix, no need to rock the boat. I don't use worm castings because they fill air pores and the micronutrients they supply can easily be provided by a number of either chemical or organic sources.
Oh - for those in the PNW, it's important that any wood products you use were not ponded in salt water. High sodium content interferes with water and nutrient uptake.
I can say from my limited experience that the "dead" container plants which I have taken apart have had very densely packed roots with rock-hard soil. I can see the logic in the above explanation and will consider these concepts in my next container planting. My eyes have also been opened to the idea of changing out container soils more frequently.
I have a question; for large containers, how would the PWT and GFP be affected if the bottom third or so of the pot is filled with course leaves & grass clippings? Would that effectively drain the soil as recommended?
Thanks so much for the information and advice.
No! To use high % of organic material in container bottoms, especially anything that quickly decomposes, is a recipe for complications. If you want to drain your containers - use a wick, not a "drainage layer". Drainage layers save on the amount of soil you use and can make containers lighter, but they do not facilitate drainage unless the particulates in the drainage layer are no more than 2.1 times the size of particulates in the soil above.
Ruth, I finally found some bark "nuggets" at one of the lumber/hardware stores here. I will look at the bag tomorrow and see what brand they are and if it says what kind of tree.
I think it sure does look like Ponderosa. I would think you have a lot of pine bark over there. But, I thought I was going to have to use the course cedar or fir bark mulch until I found this.
Will let you know tomorrow.
Al, I bought 3 planters today at a moving sale that the pots in the hangers are, believe it or not, crockpot liners!! They look real nice but, of course, no drainage holes. If I can't find any way to get holes in them what do you think about running a wick from the top down and back up again and over the lip?
Does that look funny when you imagine it?
The only think I can think of is a star bit but then would probably break them. They fit so nice and really look good. If not I will probably look real hard to find something else that fits.
I have quite a bit of experience in drilling hard materials, with 30 yrs in the glazing contracting business (glass company). We regularly drill all sizes of holes in glass/mirrors, granite (shower door installations) and other vitrified materials (the objects people bring to us to drill holes in).
Ease of drilling varies with the hardness of the material, of course. A crock pot liner will be very hard, but I've drilled a few Corning-Ware containers & it can be done. Most containers you'll encounter can be drilled with a "spear-point" drill. I'll link you to a picture from one of our suppliers. The drill is also called a 3-point drill. Highly vitreous containers (glass, or glass-like - ceramic - clay fired at high temperatures) may even require a diamond impregnated "core drill", but it's uncommon to find containers like this.
These drills can be found at big box home improvement stores. They should be cooled with water or a 50/50 mix of water/antifreeze as you drill. An excellent strategy is to immerse the container upside down in a tub and add enough water to just cover the drilling surface as you drill. Rotating the drill clockwise at a slight angle while drilling will greatly increase efficiency & speed of cutting. Be patient & use moderate pressure - let the drill do the work. Alternately (I use this method), fill a squeeze container (contact lens solution bottle is stellar) with water & squirt it at the drill/material interface as you drill. If you can't find the drill you need, you can contact me off forum & I'll be glad to help you.
See one here:
Alternately, you could set a block in the bottom or partially fill with gravel & use as a cache pot.
This message was edited May 6, 2007 8:45 AM
So glad to see this thread/topic continuing. Thanks, Al.
By the way, does someone know how to convert cubic feet to gallons? In the "big batch" recipe the peat and perlite are given in gallons, yet the pine fines in cubic feet. In other words, how many gallons equal 3 cubic feet? (I get pine fines by the trailer load, not by the bag.)
Sign me, Seriously deficient in math conversions!
US gallons, dry: http://www.metric-conversions.org/volume/us-dry-gallons-to-cubic-feet.htm
Roughly 6.5 US gallons,dry, to 1 cu ft.
I tried both names for it and they couldn't find one.
Those ideas sound like a good way for me to get electrocuted. LOL
Is there a difference between pine bark and pine bark "fines"? None of the outlets seemed to have heard of PB "fines" but I did pick up and have started to use pine bark. The sizes of the pieces vary of course but they're far from "fine" -- many as large as 3" in length. I have repotted a couple of plants into a mixture of:
5 pts PB
1 pt spag peat
2 pts perlite
and after three days they seem to be doing fine. Am I on the right track? Thanks
Pine bark fines are small pieces of pine bark that are partially composted (see them at the top in the picture). Pine bark is uncomposted bark and comes in various sizes (see them at the left in the picture). You probably don't want to use uncomposted bark larger than what you see in the picture. It will be really difficult to keep watered. Running large particles through a chipper to reduce their size is helpful.
I think we're getting off on the wrong track here. If you cannot find the right products, you're probably better off to stick with what you know. Particle size is important for drainage, aeration, and a soil's ability to hold water. If you try using something with huge particles, I'm afraid you'll be disappointed.
I can tell you and show you what makes a great soil, but if you don't have appropriate ingredients, then "close" can be frustrating. I'm not trying to insinuate that anyone should use what you guys call "My Mix", or that it will somehow transform you into a fantastic grower overnight. It won't. I just know that it works extremely well & have received the same feedback from easily over 100 people I have helped - lots of evidence of that here on this and other forums. It is very forgiving because it's difficult to over-water, and the high air volume it holds promotes excellent root health, which translates to good vitality in plants growing in it.
So - if you can find the ingredients, you'll be pleased with the results; but if you can't find them, default to what you know.
Is this type of soil mix also applicable to leaf veggies in containers such as lettuce and spinach?
At the bottom of the bag of pine nuggets/chips I found the smaller ones and used them.
Al, I think what I am using and what Michael is using is more like the 9 o'clock with maybe 1/4 of it larger pieces. But, I don't know why even the larger pieces wouldn't be ok. Wouldn't the manure and the peat or pro-mix which I used, work into the cracks and crevices somewhat of the larger pieces? I will keep an eye on my tree peony this summer and see if it appears it is drying out too fast.
Thanks for the reply and advice about not getting too deep into information with only a little knowledge. (As my grandmother often said: "Information is knowing that the toilet is about to overflow, while knowledge in knowing what to do about it.")
the fact is That I'm only repotting a few plants to your recipe in the hope I'll learn something with the experience. But I DID remove the styro peanuts from many of my plants and planned on doing this as I pot up the other ones. PLEASE say this is the right thing to do. The media I use is either Schultz's Potting Soil Plus or my own recipe of 1 pt regular potting soil, 1 pt Perlite and 1 pt spag peat. And in some cases, for sand loving plants like Dahlia's, I've added 1 pt sand.
The peanuts/rocks/gravel for drainage myth really has a life of its own, doesn't it? I have repeatedly referenced this thread and a couple of other secondary sources in the Plumeria forum, the Greenhouse forum, and elsewhere. In one case, Al, I was asked for original data. I spent a good deal of time on the internet looking for primary data without success. Do you have any original sources to which you can refer me?
I would like to add that coconut husk chips (CHC) make a very suitable substitute for pine bark. My CHC recipe turns out to be otherwise very similar to Al's Original Recipe.
SB...thanks for the conversion info on the cubic ft to gallons. And I appreciate the link to the conversion website, too! Will be sure to save it. Much obliged.
I found what I think will work in my mix for pots. It is called mulch at Wal Mart. They have three sizes of mix. I got the smallest, and of course on the bag doesn't say pine, fir, or cedar. I'm pretty sure it isn't cedar, but not sure which of the other two it is. Some is too fine so guess I will have to screen it.
Al, if you mentioned either use or not use some kind of water crystals in the mix, I missed that. Do you use any kind of water crystals. This climate is extremely dry. since the first of Feb. we received measurable rain once for about 10 minutes and i think it was last Monday it rained softly for about 4 hours. Even with using some kind of drippers in the pots and a timer it is difficult to keep the plants moist enough.
Donna, I will check that out at Wal Mart. You say you got the smallest? One of these days we will make the trek to Colville. LOL With the price of gas we hold our trips to a minimum as do most people now days.
R - If I said the wheels on the bus go round & round, I'm sure someone would ask for the original data. ;o) It doesn't matter to me if they believe or not. A perched water table is something that is common to the earth's geology. In fact, the idea came to me while having a discussion about the earth's water tables WITH a geologist. I won't go through the effort of convincing naysayers; instead, I'll lay the onus of disproving what I say on them. Perhaps we can learn something in their attempt. These comments are not directed toward you. I know you're convinced the concept is applicable & I respect your views & constructive offerings. Thank you. ;o)
I have pretty regular discussions with people with doctorates in soil science or related fields, and perched water tables & the saturated soil at container bottoms is frequently discussed in detail. The 2.1X gradient differentiation between particulate sizes that determines whether a drainage layer is effective or not was taken from a recent letter from a doctored correspondent and was the result of some research he'd undertaken.
Tell doubters to: Lay a saturated sponge flat on a piece of hardware cloth (1/4 inch mesh wire screen) until it stops draining. Lift the sponge until its longest edges are vertical. A considerable amount of additional water will drain. After it stops, grasp the sponge by a corner & still more water will drain because the perched water has less volume of sponge material to occupy. This easily confirms the existence of a PWT. If that's not proof enough, they can perform the experiment with a Dixie cup full of wet soil & wick.
Donna - I don't use polymer crystals because I make the watering rounds daily and there is no reason to. There are other reasons too, that are mentioned in the last 1/3 of the original post if you would like to review it.
Never mind - I knew where it was, so I retrieved it for you:
" Though it may not be as important for the plants in container culture, we as consumers might want to think about what we use in the way of water absorbing soil amendments and how we use them. They do persists in the environment & have no nutrient value to flora or fauna!
Some of the "extra-absorbent" characteristics mentioned by manufacturers of polymers are exaggerated, & as bio-degradation occurs these polymers actually reverse their effect and hold moisture so tightly it is unavailable to plants. Soils can usually be designed so forest products (bark), peat, and other organic media components that adequately hold moisture can be used with no ill effects. These products, even in containers, provide the plant(s) some nutrient value & fodder for the micro-organisms that polymers inhibit. Some degraded polymer components even have some of the same effects on mammals as female hormones, which can affect mammalian fertility and potency.
Additionally, and as you alluded to, the polyacrylamides in some garden-grade moisture holding polymers are made from (& contain) the monomer acrylamide, a known carcinogen."
I bought some of the polymers just to see if they have improved them.
Many years ago I tried them and my begonias did absolutely nothing. Did not grow!! When I finally took them out of the pot the roots had grown into the crystals and never left them. I am thinking it was my fault maybe I didn't water enough. Or something. I decided to try them again but am almsot afraid to. LOL
I have a lifetime supply if I never use them.
Hi Jeanette, How are ya! I've been lurking.
My brief forray into polymers was not a positive experience and will leave that science to the deserts of the world. Meanwhile, my first re-pottings using the wick and recipes of those 1.5 inch cuttings of the Hibiscus from Hawaii are growing and lilke happy wild, and is getting ready to bloom profusely. One of them is now taller than I am. All of my past potting folleys are now blatantly obvious!
Hows things? Send me an email.
You know Randy, those emails go both ways. LOL. Will do.
FWIW, I have a Japanese maple in a pot in the sun using the crystals. We've had a few days into the low/mid 90's already this year and so far not showing any real stress.
Not an ideal datapoint, I know. This is the first year I've done a lot of containers and first time using the polymers. Using 3 Tbsp/5 gal of potting soil and I'm hydrating the crystals before mixing them in.
It won't be long before we'll see some 100+ degree days and that will be the real test. I don't water the pot every day even with the heat we've been seeing. For underplantings I have a couple of Coleus plugs and a little Bacopa draping over the edge.
Also used them in a strawberry pot with African daisy up top and Coleus in the side holes(wizard mix). The daisies aren't exactly thriving, but the Coleus in the side holes is going gangbusters and again this gets tons of sun, with only slight dappling from a nearby Queen Palm in the middle of the day.
I have had nothing but positive experience with crystals. If you want to water every day, sometimes two or even three times, don't use them. I have other things to do. Crystals and mulching really helps with pots and baskets.
What are your thoughts on cocoa hulls instead of pine bark fines? Aren't they roughly about the same size? I don't want to have to buy a bag of pine mulch if most of it is large chunks just to get small pieces. If cocoa hulls would work, I'd buy a bag and use it just for container mixes.
Read this: http://forums2.gardenweb.com/forums/load/contain/msg0521180225270.html?7
Strong opinion, Victor ..... Personally, I use very fast soils and have nothing but positive experiences to report with them. I view frequent watering as a substantial benefit to plants, as long as you're willing and able to keep up. Try to remember that everyone reading these forums does not hold convenience as their focus. Some are willing to sacrifice some convenience for even small gains in plant vitality.
Al, I'd love to have the time to do it - I just don't. With two young boys, it's impossible. When I do water, it takes at least an hour to do all my pots, window boxes, hanging baskets, etc. I could never to that every day, let alone more than once a day. In my case, it's all annuals anyway.
Completely understand. Often soil choice is a requisite compromise. ;o)
Thanks for the link. I go back and see what else I can find instead of cocoa hulls since they list names of the products they found to work.
I feel the bag of fine mulch that I bought at Wal Mart, is going to work out good. I think it is pine, no large pieces, all are less than 1/2 inch and most are smaller than that.
OK, i'm sold.....will cypress mulch work? i have 2 bags left over from last year. The "fines" look like the right size.
Donna, I bought some of the bark mulch at WalMart after reading your post. It really is small. But, interesting. The bark that I got first, think it is fir, and planted my tree peony in is a lot larger than these. BTW, my tree peony I planted about 2 weeks ago is beautiful. I think. I will try to post a picture of it. I am not great at pictures so give me a break. LOL
JS - I was on a question/answer panel for a garden group recently and one of the other panel members cited a recent university study on mulch materials. The study reveled that plants grown under cypress mulch showed less increase in biomass than those grown under any of the other mulches - including ground up tires. The conclusion was that cypress wood products are, at a minimum, mildly allelopathic. For that reason, I would stay away from them, and particularly in containers.
Al, thank you very much for your timely response. I vaguely remember hearing something about that a while back. I'm glad I asked. Off to the store to get more "soil conditioner".