Do you start each season with new potting mix or do you amend what you already have in your pots? If you amend, what do you do?
Would love to hear what everyone does!
Suggestions for amending container potting mix/soil?
Glad you asked the question Becky.
I amend commercial potting mixes with our compost and some bagged topsoil .
We have clay here so I wont use it in containers.
I amend potting soil with perlite. The amount depends on the plant and whether it likes a constantly moist soil or likes to dry out a bit between watering. I use a lot on cactus and succulents.
Becky...I replaced about 1/3 of last years soil with equal parts of mushroom compost or Black Kow and Soil Conditioner (narturescapes) found at the Big Box stores. You can use mini pine bark nuggets if you can't get the soil conditioner. Mix it in with the old soil...add a little bone meal and your good to go! I don't think in today's economy that we can afford to replace all the soil in our pots. At least I can with over 20 containers.
That makes sense. I have containers of coleus and the commercial planter mixes need something to hold moisture.
They (18") dryout in a day.
I aslo amended with crystals last season
Thanks for the Big Box hint.
You are right I only replace the top 1/3 .
From one of my replies to the same question. It is a cut/paste job, so keep that in mind if you decide to read it:
In my estimation, the only case to be made for reusing container soils is one of economics, and you'll never find me argue against making that decision. If you can't afford, you can't afford it. That said and setting economics aside, you might decide to reuse soil for reasons other than economical. Perhaps the effort involved with acquiring (or making your own) soil is something you might not wish to go through or be bothered with.
In any case, it would be difficult to show that soils in a more advanced state of structural collapse can somehow be preferred to a soil that can be counted on to maintain its structure for the entire growth cycle. So, if the economic aspect is set aside, at some point you must decide that "my used soil is good enough" and that you're willing to accept whatever the results of that decision are.
All soils are not created equal. The soils I grow in are usually pine bark based & collapse structurally at a much slower rate that peat based soils, yet I usually choose to turn them into the garden or give them over to a compost pile where they serve a better purpose than as a container soil after a year of service. Some plantings (like woody materials and some perennials) do pretty well the second year in the same bark-based soil, and with careful watering, I'm usually able to get them through a third year w/o root issues.
Watering habits are an extremely important part of container gardening. Well structured soils that drain well are much more forgiving and certainly favor success on the part of the more inexperienced gardeners. As soils age, water retention increases and growing becomes increasingly difficult. If your (anyone's) excellence in watering skills allows you to grow in an aging medium, or if your decision that "good enough" is good enough for you, then it's (your decision) is good enough for me, too.
The phrases "it works for me" or "I've done it this way for years w/o problems" is often offered up as good reason to continue the status quo, but there's not much substance there.
I'm being called away now, but I'll leave with something I offered in reply on a recent thread:
"... First, plants really aren't particular about what soil is made of. As long as you're willing to stand over your plant & water every 10 minutes, you can grow most plants perfectly well in a bucket of marbles. Mix a little of the proper fertilizers in the water & you're good to go. The plant has all it needs - water, nutrients, air in the root zone, and something to hold it in place. So, if we can grow in marbles, how can a soil fail?
Our growing skills fail us more often than our soils fail. We often lack the experience or knowledge to recognize the shortcomings of our soils and to adjust for them. The lower our experience/knowledge levels are, the more nearly perfect should be the soils we grow in, but this is a catch 22 situation because hidden in the inexperience is the inability to even recognize differences between good and bad soil(s).
Container soils fail when their structure fails. When we select soils with components that break down quickly or that are so small they find their way into and clog macro-pores, we begin our growing attempts under a handicap. I see anecdotes about reusing soils, even recommendations to do it all over these forums. I don't argue with the practice, but I (very) rarely do it, even when growing flowery annuals, meant only for a single season.
Soils don't break down at an even rate. If you assign a soil a life of two years and imagine that the soil goes from perfect to unusable in that time, it's likely it would be fine for the first year, lose about 25% of its suitability in the first half of the second year, and lose the other 75% in the last half of the second year. This is an approximation & is only meant to illustrate the exponential rate at which soils collapse. Soils that are suitable for only a growing season show a similar rate of decline, but at an accelerated rate. When a used soil is mixed with fresh soil after a growing season, the old soil particles are in or about to begin a period of accelerated decay. I choose to turn them into the garden or they find their way to a compost pile.
Unless the reasons are economical, I find it difficult to imagine why anyone would add garden soils to container soils. It destroys aeration and usually causes soils to retain too much water for too long. Sand (unless approaching the size of BB's), has the same effect. I don't use compost in soils because of the negative effect on aeration/drainage. The small amount of micro-nutrients provided by compost can be more efficiently added, organically or inorganically, via other vehicles.
To boil this all down, a container soil fails when the inverse relationship between aeration/drainage goes awry. When aeration is reduced, soggy soil is the result, and trouble is in the making."
Wow! Some great input by everyone! It is an economical thing for me to try to reuse some of my potting mix the following season, but I am also known to dump the mix into my garden beds after a season if the potting mix looks pretty leached. Which often it does.
Al - I can honestly say that I agree with you about what compost does to garden soils. That is something I have noticed over the few short years that I have been gardening. When I add compost too thickly to the top of my garden bed soil, it compacts and makes the soil horrible. I read somewhere that to use compost in a garden bed, you have to dig a deep trench and then add compost. Then cover back up with the original soil. The soil has to be fluffed up to make it usable again. Apparently the roots get the nutrients from the buried compost? What are other ways that you would use compost instead for improving garden soil? Compost tea? My roses love compost. They are in pots, not the ground. I add it to the top of the potting soil. I am going to have to figure out what to do with roses in the pots. Do I change out the top 1/3 of the soil to keep the roses happy? I am like many ... I can't afford to replace all that soil.
I also need a good compost tea recipe. Does anyone have a good one to share?
It seems to be a constant battle to keep the garden soil as well as the potting mix/soil healthy to grow my plants healthy. It's very frustrating!
I don't use compost in container soils because its small particle size guarantees too much water retention to suit me. Finished compost is very fine, and if the compost is in larger pieces it's not finished, in which case N immobilization becomes a problem.
You really can't amend compost or used potting soil with perlite and make it drain well. Adding perlite to compost doesn't change the drainage characteristics of that blend any more than adding perlite to pudding does. If you add perlite to compost, the height of the perched water table (PWT) remains the same, until you have considerably more perlite than compost, only then would you see the height of the PWT reduced. The value of mixing perlite into fine media components doesn't technically come from improved drainage, it comes from the fact that perlite doesn't hold water internally, so there is less media in any given volume that holds water. IOW, it doesn't make soils drain better unless it represents the primary fraction of the medium, it simply reduces the amount of water any given volume of medium will hold.
It makes good sense, if you wish to reuse container media, that you mix it sparingly with a component or components with larger particle size, which is why I prefer pine bark as the primary fraction of some of the soils I use. If you mixed your used soil with 5 parts of inexpensive pine bark fines and 1 part of perlite, to 1 part of your used soil, you'll end up with a durable soil that will remain well-aerated far longer than a peat based soil. On a size for size basis, pine park breaks down at about 1/4 the rate of peat, so when you consider the much larger particle size, you should expect a bark-based soil to retain its structure more than 5 times as long as a peat-based soil, all other cultural conditions being equal.
I enjoy reading your soil posts, Al. I learn from you every time. I will apply your very practical container knowledge to my whole gardening knowledge. I plan to rework most of my potted plants this year, and I still have a big supply of pro mix. I am planning on using some for veggies, as they go in the ground and the peat gets mixed into an ocean of clayey dirt. The rest, I don't know yet. Maybe we can use it for striking cuttings of raspberries or blackberries and getting more planted around here. I love to go berry picking with the kids. And the jelly is pretty good, too :).
Do you mix pine bark fines into your garden soil?
I am going to attempt to make some cheap self-watering containers:
Would using pine bark in a container that is self-watering work?
Perlite is unbelievably expensive here as is bags of potting mix. What is the difference between potting mix and potting soil?
How expensive? I was using the 8 quart bags way too often, so I found a 4 cubic foot bag online. It was reasonable and I can use all I want... There is a local place that sells the 4 cubic at a good price but they won't stock any until spring and I needed it in the fall.
Becky - some people try to draw some kind of differentiation between potting soil and potting mix by saying that potting soil contains some form of mineral (garden soil/topsoil) and should be avoided, but I've never seen that to hold true, so I use the terms interchangeably, and even add media/medium in as other synonyms. I agree, and think the majority generally agree that mineral soils are undesirable in container soils because of the negative affect they have on aeration.
I know several people that use Fafard's fine pine bark as the primary fraction of a 5:1:1 mix of pine bark, peat, and perlite with very good results. If you use a bark product that is more coarse than the Fafard's, you'll need to add an extra measure of peat to increase the soils ability to wick. FWIW, making your own bark-based soil will leave you with a soil that costs less than half of what a commercially packaged soil costs and one that will retain its structure far longer.
I think that if you look in the right place, you'll find perlite is quite inexpensive. I buy 4 cu ft bags here for around $15. Look to good size nurseries or greenhouse operations that do their own rearage, which means they are likely to be making their own soils. Most, if they don't have it on hand, need only to add it to their next order from their wholesaler and will likely be glad to do so.
Thank you for the very kind words, Dawn. They are appreciated. Whenever I write something, it's with the hope that those reading it will find a way to use the information to help them increase the amount of satisfaction they get from their growing efforts.
I just noticed that my reply post never got posted here. Grrrr ... I've been having problems with my internet service lately. So here goes a second try ...
Al - Thank you for posting to this thread! I value your information and insight. I am a bit frustrated with my local nurseries. Apparently they are out to make a nice profit off anything they sell. Perlite here goes for about $6-8 per 8 oz. bag. I am going to use self-watering containers. I do have Spaghnum Peat Moss (from Canada), I will buy more Perlite, and will see if anyone carries Fafard's fine pine bark locally.
I do have a question though ... I am still hung up on compost for the micro-bacteria. I have heard of potting soil recipes using compost (high-quality), sphagnum peat moss, vermiculite (hard to find cheap here) and/or perlite, and limestone. I know many people that garden for veggies uses that mix with excellent results. They also use fish emulsion as the main fertilizer. That mix I've been told keeps the plants very healthy and hydrated. And I was told they reuse the soil by mixing in more compost and rotating the crops. So after the initial costs to create this potting soil, they just mix in compost (and perhaps some lime) with additional plantings. That sounds very economical to me. Does Canadian Spaghnum Peat Moss breakdown slowly? I know perlite doesn't break down. I've been told that this soil mix works very well in self-watering containers and cuts down on the amount of time you have to spend watering the plants. I live in Florida and the heat dries the soil very quickly unless the pots are self-watering.
Why would compost "not" be a good thing to use if it is used in moderation with a well aeriated soil mix?
I've been doing more reading (with my head once again swimming with questions (sigh))...
Fafard's Organics Potting Mix keeps coming up in threads. Is this stuff as good as trying to make a good organic potting mix yourself? I am trying to figure out the most affordable, yet still great potting soil mix to grow plants (mainly veggies and fruit) in self-watering containers.
Have you used or heard about this product, Al?
I found a nursery about 6 miles from me that sells Fafard soil. If it's any good, then I may have a source to just buy my potting mix. My biggest problem with making my own is finding the ingredients at an inexpensive price. I have to keep my costs down to make it even worthwhile to growing my own veggies. Otherwise, it's cheaper to just buy them. Ordering ingredients online is available, but the shipping is very expensive!
This message was edited Dec 29, 2009 4:56 PM
Becky - I'll try to follow right through your posts with my offerings.
The price problem with the perlite is the size of the bag you presently have access to. As the volume of the bag goes up, the price will fall dramatically (on a per volume basis).
In my considered opinion, compost is ok if used in container media in moderation. I would limit the total peat and compost fraction combined to under 15% of the mix in favor of pine bark as the primary fraction in my soils for garden display and veggie plantings. In the gritty soil I use, I don't ever use peat or compost.
The most important aspect of container soils is the soils structure and its ability to maintain that structure for as long as the planting will remain in that soil. On a scale of 1-10, if growing in the garden is a '1' and hydroponics is a '1o', conventional container culture is about a 7 or 8. This means that growing in the garden and growing in containers are distinctly different cultures, and what works in the garden often works poorly in containers. Those rich, black humusy soils we covet in the garden are water-retentive and poorly aerated in containers. The soil biota you covet from compost comes at a price. First though, consider that soil organism populations are boom/bust in containers, so you cannot rely on their numbers. While they do help to break media components down into usable nutrients, you should know that the media actually supplies such a small part of the planting's nutritional needs, that you would be much better served to proceed as though it provides no nutrition than to count on it as of any significance as a nutrition source. In short you're left with very fine particulates in the hope they promote soil biota that is unimportant to your plant's vitality. Compost doesn't provide any significant nutrition to containerized plants.
While I adhere tightly to the concept of 'feed the soil and the soil will feed the plants' in the gardens and beds, I take a completely different approach to container gardening. That isn't to say I don't make allowances for those bound to a particular ideology (all organic methods), but if you're results oriented, then a well-aerated medium and soluble fertilizers will be far more forgiving and much easier to grow in than compost and fish emulsion.
How fast peat breaks down is relative, but pine bark breaks down at about 1/4 -1/5 the rate of peat, so it lasts 4-5 times as long if the particle sizes are the same. Since the particle size is almost always larger, it lasts even longer than mentioned.
Fish emulsion is not soluble to a significant degree, so it requires the same biotic activity of soil organisms to make it available. Since those populations are erratic in containers, so is availability and delivery of the nutrients locked in the hydrocarbon chains.
I didn't suggest Fafard's Potting Mix, I referred to their fine pine bark as a good source of bark for SWCs. They have several potting mixes, but the one with the highest pine bark content is best. It will be much more expensive though, than making your own. If you do decide to use their mix, mixing it 50/50 with pine bark and a small fraction of perlite + a little garden lime will give you a good mix.
After you have the bark, perlite, and peat, you should be able to make 3 cu ft (about 25 gallons) of potting soil for about $9.
Al - You have the patience and calm of a saint! Thanks for trying to help me!
$9 for 25 gallons of potting soil sounds like a dream!
Perlite - I will try to get a local nursery to order it for me. The biggest bags I've seen have been 4 quarts for average of $7. There is an online source that sells it reasonable, but the shpg is outrageous!
Pine Bark Fines - I don't even know where to look for this. All the Pine mulches sold here are larger chunks and pieces of pine. I will check into Fafards. Do you have any company names that sell this other than Fafard's?
Peat - Would Canadian Spaghnum Peat work? That I can find in large bags. :-)
Would Osmocote CRF work? That is readily available here.
I have confidence you'll be able to get the perlite at reasonable prices (
I'm not sure where the rest of my message went, the forum spirits must have eaten it.
I have confidence you'll be able to get the perlite at reasonable prices. The larger the volume in a single bag, the less expensive it is on a per volume basis.
Canadian sphagnum peat is fine, as would be any type of sphagnum peat. Just be sure to avoid bagged reed/sedge (aka Michigan) peat.
I don't know what to tell you about the bark fines. What it's sold as varies widely. I've purchased it packaged as pine bark fines, soil conditioner, clay soil conditioner, composted pine bark, ground pine bark, premium pine bark landscape mulch ..... The Fafard's pine bark product is great for SWCs, but a little on the fine side for conventional containers; still, it's much better than peat as the primary fraction of soils for conventional containers.
Osmocote is as good as the next CRF brand, if you're sold on their use. If you're sure you'll be diligent about fertilizing when needed (about every 2 weeks) you can do better with a product like Foliage-Pro 9-3-6, which has all the essential nutrients in favorable ratios. A close second to the FP would be any of the other soluble fertilizers (MG, Peters, Schultz) in a 3:1:2 ratio (24-8-16 and 12-4-8 are other examples of 3:1:2 ratios). If you're going to use a CRF, please try to get something that is as close to a 3:1:2 ratio as possible and that includes all the minors. I know that Dynamite has a formula that would work very well. I won't bother to, but it's easy to make the case that 3:1:2 ratio fertilizers are a much better choice than 1:1:1 ratios like 14-14-14 or 20-20-20.
Al - I got really lucky today! Made a bunch of phone calls to all the area nurseries to try to find Pine Bark Fines and a large bag of Perlite! Well, guess what? I found a small nursery that carries both as well as all kinds of other garden soil stuff! I bought 3 large bags of the PBF for $10 and the large bag of Perlite for $12. Whoo hoo! Most of the 15 nurseries I called didn't carry large bags of either. And we all know the big box stores don't either. So boy oh boy was I lucky! Now I have a source.
I did go to one of the big box stores for other stuff and bought Osmocote. I picked up and put it down and then picked it up again. (sigh) When I read Controled release fertilizer, I was thinking that meant time-released which is why I bought the Osmocote. I did see the Dynamite there and almost bought it instead. I will take the Osmocote back and exchange it for the Dynamite.
I do have some of the Foliage-Pro 9-3-6 in liquid form. I purchased it online awhile back after reading one of your older posts about it. I've used it, but didn't see too much of a difference in my plants. Maybe I was expecting some impressive growth or something. LOL!
So it looks like I have just about everything to create your potting mix except one item...
1/2 cup micronutrient powder (or other)
What is that? Like Mushroom compost or something. Or are you talking about dry Mycorrhizae powder or something? I was confused on what exactly I am looking for.
I also bought a 1 gallon container of Alaskan Fish Emulsion, too. Would that be considered a micronutrient? Unfortunately, it is in liquid form not a powder.
Woo hoo for getting the ingredients so reasonable and have a place to go back to for more :). Al told me that if you use the foliage pro, it has all the micro nutrients in it, so you could skip the powder if you can use FP 936 .... That and gypsum are on my list of things to get when I can find/have money at the same time :).
What is gypsum used for? I didn't get any of that!!! Please tell me that I am NOT still missing one of the magic ingredients!!! =8^O
I did also return the Osmocote and got Dynamite instead for Flowers and Vegetables! It also has micro-nutrients in it. It is pellet form. Is that what is needed? Pellet form and not liquid form?
See! What seems perfectly clear to most gardeners is confusing to a klutz like me! (sigh)
I also had my dh drill the holes and cut the PVC piles to make the 5 gallon bucket self-watering containers. We ruined a couple of the buckets by miscalculating the hole sizes, but finally got it just perfect. I gotta tell ya ... it's gonna make SWEET self-watering 5 gallon containers! My pole bean plant is all ready to be transplanted into one of them. Tomorrow is the day to try it out. So ...
Al - which fertilizer do I use? Liquid Pro-foliage or Dynamite slow-release pellets when I mix the potting mix ingredients and fill the pots?
This message was edited Dec 30, 2009 9:15 PM
Hi, Becky. I think it's great that you scored all the ingredients to make what I'm sure is a soil you'll be very happy with. You called it my soil, but really, it's going to be YOUR soil. I think the most valuable thing I can share isn't a recipe; rather, it's the information that allows you to determine WHY particular ingredients, when combined, are apt to make a soil that will suit your individual needs, and then how to combine those ingredients to achieve a desired result. My primary focus is always to give YOU the control and flexibility, and not tie you to a recipe. At the same time, I realize you have to start somewhere, so I provide a good place to start - a recipe. ;o)
I want to mention something about why you might not have noticed a significant difference when you switched to the FP 9-3-6. There are 6 factors that affect plant growth and yield; they are: air, water, light, temperature, soil, and nutrients. In container culture, it is the STRUCTURE of the soil, rather than what the soil is made of, that is most important. Liebig's Law of Limiting Factors states the most deficient factor limits plant growth, and increasing the supply of non-limiting factors will not increase plant growth. Only by increasing the most deficient factor will the plant growth increase. There is also an optimum combination of the factors and increasing them beyond optimum, individually or in various combinations, can lead to issues as problematic as deficiencies (or even cause [antagonistic] deficiencies). In short, what I'm saying that if there are other limiting cultural factors, you may not be able to detect an improvement in vitality or growth, even if the nutritional program was perfect. I think that with an improved soil, you may eliminate some limiting factors, and that should allow the plant to grow at much closer to its genetic potential so it is actually possible to realize a noticeable benefit from the FP. Since you have it, and I (and many others I've helped) know it to work very well in combination with the soil you'll be using, I would encourage you to give it another try in the new soil. ;o)
I use two chemical micro-nutrient supplement preparations. One is soluble (STEM), the other is insoluble (Micromax). I use them as insurance, but many growers don't use them. The FP has all the essential nutrients, and the only ones lacking in other commonly found soluble fertilizers (like MG, Peters, Schultz ....) that are likely to be deficient in a bark-based soil are Ca and Mg, which you'll be supplying with the lime. You can also use the Earth Juice micro-nutrient preparation, 'Microblast' if you would like .... but it looks like, at this point, you have everything.
How large/small are the bark pieces/particles?
I have several fish emulsions on hand, but I just don't use them on my container plantings any longer. I like the total control that soluble fertilizers give me - knowing exactly what nutrients I'm applying, in what dosages/%s, and in what ratio to each other, as well as I like the fact that I can depend on the fact that whatever I apply is in elemental/ionic form and immediately available for uptake.
I SO wish you well! ;o)
Al -Here is a photo of the size of particles of my three main ingredients for the potting mix. Does the different ingredients look about the right size?
The fertilizer I have is the Dynamite continuous slow release pellet fertilizer:
It is a 13-13-13 (not a 3-1-2) blend that also has Mg 1.20%, B 0.02%, Cu 0.05%, Fe 0.20%, Mn 0.06%, and Mo 0.02%. The pellets release the fertilizer for up to 9 months.
And of course, I have the FP liquid fertilizer.
So you are saying NOT to add any fertilizer pellets into the potting mix? To just water in some FP when watering the plant?
This message was edited Dec 30, 2009 10:57 PM
I am so envious of your bark. I looked and called everywhere nearby and nobody had good bark (besides my sweet hounds). Maybe in the spring, and I'm buying a truck load!
I looked at the receipt again and the perlite was actually about $13. Still a very reasonable price for 4 cu ft.
I will be making up a couple of the self-watering containers and adding in some of my veggie plants tomorrow. Here is a photo of the constructed buckets. Looks like it is going to work rather nicely. Fingers crossed!!! I decided to use PVC. Right on the PVC it said "Drinking Water", so I am being optimistic and hoping that they no longer put toxins in the PVC. The PVC manufacturer has a website: www.charlottepipe.com . It appears to be produced in Florida. I will be checking their website to learn more about the safety of their PVC products.
PVC is what likely runs the water to your house and throughout it, too, unless you live in an older neighborhood. At least in this area, waterlines are made of pvc.
3jsmom31 - I looked at the bag of PBF and it says:
Packaged for Pine Tree Products
Pompano Beach, FL 38069
Maybe they sell this stuff in KY? Might be worth contacting them. I wonder if they have a website? Maybe google for Pine Tree Products, Pompano Beach, FL
My house has PVC. In another thread there is talk about the use of PVC. Supposedly, after 1977, PVC was changed and is supposed to be much safer. I guess they no longer use any toxic PVC. That's what I would think anyway...
Hi, Becky. Can we back up for a second? There was so much activity on the thread that I momentarily lost track of the fact that you were making SWCs. I don't use them, but generally it's suggested that you use a granular fertilizer (looks like what you might use on a lawn or spread on a garden) in a fertilizer 'strip' on top of the soil. I do know that many growers forgo the granular fertilizer in favor of a soluble fertilizer (not fish emulsion) in the reservoir. I don't SEE any problem using a CRF OR the soluble fertilizer, but I'll check with a friend who is well-versed in SWCs and what does/doesn't work well. If you do use the CRF, incorporate it, don't broadcast it on top of the soil. Nutrient release is tied directly to temperature and exposing the prills to direct sun isn't generally considered desirable.
By the size of the bark, I think you're going to need some additional peat, so try 5:2:1, bark:peat:perlite to start. Don't forget to add a level tsp of dolomitic (garden) lime per gallon of soil, or 1/2 level cup per cu ft.
I do have the Dynamite slow-release fertilizer as well as the liquid Foliage-Pro. According to their website, the Dynamite supposedly has a coating that doesn't allow it to break down like Osmocote does in the heat. Supposed to last up to 9 months. (Or so they say.) Far better than the Osmocote. Dynamite also has micronutrients in it unlike Osmocote. I am thinking that might be the best thing to add to this potting mix, instead of the FP liquid. Or maybe I should use both?
I'll add in the extra peat. Looking at it ... I, too, thought it might need more because the Pine Fines are not composing yet in the bags. Maybe they were recently chopped up and bagged and have not had time to decompose yet. I have the dolomitic lime which I will also add in.
Do you add the Dolomitic lime for all plants, not just veggies? I may try your potting mix with my Brugs. They grow best in large pots, not the ground here. Too hot for 4+ months out of the year for them. Most of my pots will be self-watering pots. Please do ask your friend about the fertilizer for such. I really appreciate it!
This message was edited Dec 31, 2009 11:32 AM
The lime performs 2 valuable functions. It raises the media pH to a level favored by a wider variety of plants; and once the reactive phase is complete, there is a residual fraction of Ca and Mg available for plant uptake. If you're familiar enough with both the needs of your plants and are able to provide both Ca and Mg via other means, you can certainly resolve pH issues and provide for Ca and Mg via other sources, but that's kind of like making your own ketchup every time you need it as a condiment. It's a lot easier to use a product that already has all the ingredients AND tastes good, than it is to complicate things by trying to make your own from multiple ingredients.
I add dolomitic lime to all soils that have a low pre-lime pH. For other soils, like the gritty mix, I use a combination of gypsum and Epsom salts as the sources or Ca and Mg because neither appreciable change media or soil solution pH. That it doesn't raise pH levels is desirable in soils with a starting pH of around 5.8 or higher, which is the approximate starting pH of the gritty mix.
I sent an email to my buddy Dave, and asked him to look in and check on your fertilizer program. Hopefully, he's still a member, or he'll write me and I can copy/paste. I trust that his input will be very reliable.
Thanks, Al. I hope your friend does send you a reply soon. :-)
When you talk about "other soils, like the gritty mix" are you talking about the mix I am going to make or some other mix that you make?
I have been reading a book by Edward Smith called "Incredible Vegetables from Self-watering Containers. His secret soil mix is:
1 20-quart bag of mature, high quality compost
1 20 quart bag of homemade or ready-made planting mixture (sphaghnum peat, perlite, and limestone)
And then he adds to this mix to ensure that any deficient nutrients in the compost are included in the potting mix:
1/3 cup blood meal
1/3 cup colloidal phosphate
1/3 cup greensand
1 tablespoon of azomite
(The above 4 items I know nothing about.)
He mixes it all together and then uses it for the SW containers. He then supplements with liquid Fish/Seaweed Emulsion every other week after the first six weeks. I know you don't use compost and it is hard to say what nutrients are in any given compost, especially commercial compost.
But this gardener and writer claims he gets great results from this.
Seems when I get one answer, it just leads to 10 more ...
Sorry to be such a novice here! :-(
The gritty mix is a soil I make that has a 2/3 inorganic component and 1/3 uncomposted bark. I use it on long term plantings, like bonsai, the woody plants I grow on for bonsai, houseplants (including succulents and cacti). I'll leave a picture.
From all appearances, he is limiting himself by adhering to an organic approach. That is fine, as long as we realize that we are eliminating a huge portion of methodology that is capable of producing plants with better yields and better vitality with less effort and a wider margin for error.
To answer your question about what kind of nutrition you can expect from finished compost - compost provides almost nothing in the way of nutrients. It's value comes in what it adds to the moisture retention, tilth, and mineralization of mineral soils.
I'm not saying this from a defensive posture, rather, from a purely observational perspective: It's easy to claim you have a secret soil and to say that you get spectacular results from it. I could do that and get away with it much more easily than Mr. Smith could because I can point to the testimony of hundreds (if not thousands) of growers who are using it, but I don't. I can though, take you to an open forum setting and post your comments about the soil recipe you just mentioned, and soon, a large number of growers that USED to grow in similar soils but have sinced moved on, would join the conversation with their thoughts.
The gritty mix:
Thanks, Al, once again for clarifying all the confusing information out there on how to grow container plants. I am still going to try yours. I was just wondering if the compost added any nutrients to the potting mix, not trying to contradict your potting mix.
I think that I am going to go ahead and pot up a couple veggie plants today using your potting mix and my handmade SW pots. I also am going to add the dolomite into the top 3-4" of the soil and make a ring in the potting mix around outer edge of the pot and add some regular dry veggie fertilizer similiar to what they do in the earthboxes. And then add a heavy duty piece of trash bag to the top to kind of seal it all in. Then I'll just cut an x for the PVC pipe for watering purposes and however many x's I need to add plants to the pot. And then see what happens.
This year is mostly going to be experimental. I'm keeping notes. If I have great success then I will know that I've hit on something that works. If it is a complete bust and the plants do not thrive, then I will know to change my approach and try something a little different.
I hope that you hear from your friend who does SW containers. If so, please post here for me (and others) as to what he suggests or does. I greatly appreciate ALL your help. You are a wonderful "teacher" and I know that you have helped hundreds or even thousands of people with your insight into how plants grow and thrive. :-) Thank you so very much!!!
;o) I didn't take it as though you were contradicting anything, Becky. I hoped to off as not being defensive.
Incorporate the lime entirely for best results (all through the soil).
Hopefully Dave will show up. I've seen him post here, but not for a while. He's very active on a competing site with a container gardening forum, which is how I got to know him.
You're very welcome for the help. I try to help almost anyone I think I might be able to, but as you probably realize, some people are able to make us WANT to help them. Through the years, I've thought about that a lot, and I've concluded that it's not any one thing that makes me feel that way. It's more like a combination of things, but I do know that attitude plays a major part in the amount of satisfaction that I get from the interaction and from helping where I can. I guess I'm taking a circuitous route to wind up saying that I like your attitude, and that you seem like a perfectly nice person just adds to the fun.
I think I already wished you a HAPPY NEW YEAR! If I didn't, I do; but it's probably getting closer to the point where CHEERS! would be more appropriate. ;o)