I have a bunch of containers filled with potting mix from last year's containers. I also have a bunch of 1 gallon milk jugs that have potting mix in them with seeds for winter sowing. Can I re-use any of this potting soil this spring/summer for my containers? I'm guessing if I can, I should add some fertilizer. Is there anything else that I should add? Or should I just buy new potting mix?
Thanks so much!
--Pam
Can I re-use potting mix?
There are conflicting views on this. Our good friend Al (Tapla) will tell you that the thing to be aware of is that last year's mix will probably have broken down and you'll have an issue with water permeability (right, Al?). I've re-used potting mix with reasonable results, but I usually blend in some additional, new mix to avoid the problem noted above. It helps to extend the old mix. I will defer to Al, but would also say that if the mix hasn't broken down too much, I'd re-use it. Otherwise, old mix works well to amend soil in your planting beds if you have clay soil.
Logees has a Container Soil Amender (or something like that) that you add to last year's potted plants or potted soil to keep it useful. I haven't used it, but will probably order some becuase I have alot of pots from last year that survived and are still in their pots and don't need repotting.
If I ever do throw out container soil, I use it to fill in low spots in my yard.
What Steve said. I also get a bag of Vermont Compost and mix it in with my old potting soil. You can't be changing your potting soil every year when you grow perennials. My clematises wouldn't appreciate being disturbed. What I do with them is take a bamboo stake and poke holes all the way to the bottom, about two dozen or so. Then I pour the Vermont Compost into the holes and also add about a two inch layer at the top. I'm sure Tapla would not approve, but it seems to work for me. Here's one that I've done this with for several years. I have it in a large pickle crock about 13" across by 20" deep. I do use fresh soil for annuals in all my containers.
I think Logee's sells Vermont Compost, that's what jlp is referring to. You can also get it at Gardener's Supply.
Oh, you can also add GreenSand or other amendments to top dress re-enriching (is that a word?) the soil. It may not work for everyone, but it does for me.
I like my "title" better ; ) but I think you are exactly right!
All my used potting soil goes into my mulching bins when up-potting a plant or the plant has died (annuals, etc). Once the compost/soil is done, it goes into an aging barrel (screened). When potting new plants or re-potting, I mix lime, porous silica and pine bark nuggets (screened) into the mix, adjusting as needed. Sometimes I will also add perlite, peat and/or sand, depending on the needs of the plant being potted. Naturally, it is necessary to fertilize growing plants when taking this approach. I've had some pretty good results doing this, and I think it is totally consistent with Al's excellent advice. Given the large number of containers I use, it is not practical to keep purchasing new potting soil. The silica does not break down, but the pine and nutrients need replacement. I generally purchase the pine a year or two before it gets used, so this is aged as well, even if what is purchased had not been previously aged.
I really like the consistency of coco shell mulch and have been experimenting a little with it, as it can be hard around here to find pine bark small enough for my needs. Al, if you are reading this, could you provide some advice about the coco shell stuff? It would be much appreciated.
And this is the time to add a good, long lasting fertilizer, which will feed throughout the growing season. I recommend my namesake. ;-)
krowten . Quote Once the compost/soil is done, it goes into an aging barrel (screened)
What size screen do you use????..Window screen or larger???????
Thanks
Tubby
In a second, I'll leave something I wrote quite a while ago.
I haven't really looked closely at the chemical properties (pH and what elements it might include - or other potential problems/benefits) because coco mulch breaks down very quickly. Since there are other materials that are more durable and approximately the same size, I never give it consideration. I have purchased healthy individual liners (small woody plants ready to pot up) that were in coco mulch, but they were intended as very short term plantings - a couple of months instead of a whole season.
From one of my '05 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.
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 builders sand or anything finer, or compost in soils because of the negative effect on aeration and/or 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."
Al
Everything you say is true, but for some of us there are reasons other than economic ones that keep us doing what we've done before. I don't think anybody in this thread recommends keeping old soil if it can be helped. But with good reasons for not replacing soil every year we keep on doing what seems to work. If my plants suffer, then I'll worry about replacing the soil. But if not, and growth is satisfactory, then I probably won't. So different strokes for different folks.
That being said, I do replace my bulb soils each year, and use Tapla's method which has yielded terrific results.
Ahhhh. This is why I love DG! Thanks for your very knowledgeable answer, Al. I will promptly add my old container soil to my compost heap, and budget for new potting mix (or the components to make my own) in the spring. Thanks for taking the time to help out a beginner.
Thanks, also to everyone else who answered my question - didn't mean to just single out Al. It's so great to get different opinions and everyone's own unique experiences. What a great wealth of experience!
PGT - When it comes to reusing old soils, there are some additional considerations I don't think I included above. There is always the possible carry-over of fungal spores, the possibility/probability of insects in various stages (eggs, larvae, etc) and build-up of carbonate precipitates from your water. A slow soil will also have accumulated fertilizer salts and possibly insecticides that you may have applied and forgotten about last season.
I often suggest a soil with 5 parts of pine bark fines: 1 part of sphagnum peat: 1-2 parts perlite as the basic ingredients. If, by chance, you are going to build a bark based soil, and you're not too concerned about what I offered above and in this reply, you should be able to use your old soil in place of the peat component and have no worries about premature collapse.
Revclaus - Please take this as something I would offer to someone I don't want to offend. It's not meant to be argumentative - only thought provoking.
We should probably consider most of the plantings we would be discussing on this forum as a season-long or long term planting. When you say "If my plants suffer, then I'll worry about replacing the soil.", I would ask readers to consider that by then, it's too late. It's possible, but very inconvenient to correct a collapsed soil in the middle of a growth cycle (middle of summer) - and then there is the consideration of what will it do to crop & bloom yields. I think we can agree we don't want to be changing soil AFTER a planting is established. I suppose there is a little bit of "It's better to be safe than sorry" in my offering, but I've helped enough people who were growing in soils that had collapsed early in a growing season because they were used and carried over from last year to know that it's a better choice o/a to use fresh soils each year.
I wouldn't argue with anyone who has good success reusing old soil, because I know it CAN be done. I would say the range of difficulty in reusing soils would cover everything between 'not too difficult' to 'very difficult'. My experience shows me that it will always be at least somewhat more difficult at best, and varying amounts of the margin for error that is built into a fresh, well-aerated soil we can rely on to remain structurally sound for the life of the planting will be eliminated. I'm not trying to change the mind of anyone who is fully satisfied with their results, only to point out to others what they might anticipate when dealing with used container soils.
I build durability into every soil I make. All the ingredients I use are there to insure that the soil will remain well-aerated and drain freely. The bark based soils break down at a rate of about 1/5-1/4 as fast as peat based soils, yet I still choose to turn them into the gardens or compost after a single season, so sure am I that better results are to be had the next year with a fresh batch of soil.
Nice thread, PGT.
Take care.
Al
When you say "re-use" do you mean "still in the pot from last year"?
Not offended, tapla. I like a good discussion. But I want to make it clear that the only container soil I "reuse" is in pots already planted with perennials. New plants get new soil. I don't have any gardens to dispose of the old soil in, so it gets tossed. I do go through a lot of new soil every year for new plants.
By the way, can I add shredded bark to say, Pro-Mix, and have decent results? I don't have a way to concoct your recipe for container soils, not enough room. If I could get smaller bags of supplies it would be easy, but all they ever want to sell you is a ten-ton bag of stuff.
Just as a follow up, I too should mention that most of what I grow are perennials in pots for the long term. AND to point out that most of the pots have a wick, a significant amount of pine bark, porous silica and perlite. Recycling of the soil does not mean that I don't adjust these components, which I do. I build my soils as I decide what the current plant in question needs, as well as the material coming out of the aging bin. Screen size for aging is 1/2" to answer a previous question. And yes, I have made my share of mistakes in previous decades with compacted soils, have learned from it and moved on. It might help to think of the contents of my mulch and aging bins as a basic tapla mix (can we make this into a formal name?), through which are cycled old and new materials. It is simply not possible to repot/replant all that I have on any regular annual basis. I would also note that many pots are colonized with earthworms, ants, pill bugs and other biota that may help to maintain the quality of the soil. Growing is just not a function of physics and chemistry, but of ecology. (no criticism implied of anyone here, but bringing up another aspect of container growing that has not seen much discussion) I think that its about balance and balancing many factors is what makes it interesting, fun and an art.
I would love to know what you use for your wicks, krowten.
TIA ~~ Kyla
Krowten - Of course I respect your choice to grow in whatever you choose, but I have a different perspective on the used soil you are using, which essentially is compost, or close to it. I think I covered my view above, so I won't belabor the point. As far as biotic activity in the soil - there is a trade-off for its presence and that is more rapid soil collapse. A soil filled with all manner of organisms that devour soil particulates can/will quickly collapse the soil. They also easily out-compete the plants for available N, so when their populations are high much of the N supply can be immobilized in those organisms. If there is a sudden die-off of soil biota , as in when we fertilize or especially when soil temperatures rise above favorable levels common in containers (and there are other cultural conditions that generally make containers inhospitable to steady populations of soil biota) you end up with a container full of dead organisms releasing the immobilized N when the soil is too warm - not a good thing.
Rev - all bark is not created alike. Most commonly found conifer bark is suited to container culture if the size is appropriate, while shredded cypress bark/mulch and other shredded hardwood barks are not (w/o going through extremely complicated composting procedures first). Pro-Mix and pine bark fines mixed @ 50/50 should make a good soil.
Al
Al, I would disagree with your characterization of what I am using as compost. Really, when starting out years ago, I did try to use compost in pots to try to grow plants (not very successfully) and I agree with you about compaction (and other issues)when using compost. Perhaps this is a terminology issue in that my recycled potting material is placed in a compost bin with a very selective mix of other materials, some of which would qualify as compost-able, but others that break down very slowly or not at all. This mix is typically fallow for about a year before reuse and I am very selective in what gets added. For example, last year year a lot of autumn olive trimmings were added due to my needing to drastically prune my two small trees. This wood is very hard and slow to decompose. As I do sift before use, I get to see how fast various things break down. When I am planting, I amend this with stuff like fuller's earth, fired clay, porous silica, pine bark, some occasional sand, perlite, etc. I am a renter and consider part of the "growing" I do is making a valuable commodity I label "soil" which I fully expect to take with me if I ever move. That said, Al, you have helped me very much to understand why what I do works and for that I am most appreciative. However, I simply am not able to treat such a valuable material as fertile "soil" as a disposable commodity.
Kyla, I use woven nylon or polyester rope that is about 1/4-5/16" for my wicks. It is not as an efficient a wick as I would like, as it is slower in moving water than I would like to see but I do not want to use something that would decompose and have to be replaced often.
I'm learning from my garden: "If it 'ain't broke, don't fix it."
If my veggies garden continues putting out good produce, it ain't broke. When it stops doing so, I'll figure it's time to amend half or all of the soil. Until then, I'm good.
This message was edited Feb 24, 2009 12:10 PM
Krowten thank you, that was the reason for my question, as something like cotton or hemp would decompose fairly fast I would think. Thanks!
I am really appreciating this entire conversation here, and learning a lot. I doubt I will ever be as in charge of the details as the more experienced voices here but it is wonderful to be armed with information, and I have to say, I love the image of growing plants in marbles if you are willing to stand there and water them constantly, LOL!
Kyla
Wow! What I thought was a simple question turned out to be much more complicated than I thought. This has been such a wonderful exchange of information and experience. Makes me realize just how little I know about gardening. Thanks so much for all of your answers.