end of season soil

treeskate(6a Hartford CT)October 1, 2006

This was the first year I did some container planting. What does everyone do with the potting soil (plus mixed in coir for water retention) at the end of the season? I must admit I had unending joy from 2 long boxes filled with Gladiolus Callianthus Murielae (Peacock Orchids) that still are in bloom. I also had 3 spirea shrubs in large tubs in the front yard and now have installed them in the ground in the back yard. So what do I do with all this potting soil???

Thanks for your help.

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jenny_in_se_pa(USDA7 Sunset 32)

I keep mine for the next season and will pull some out and will mix in some fresh mix for replanting in the same container. The soil that was pulled can itself be mixed with fresh mix for other pots.

    Bookmark   October 1, 2006 at 11:15AM
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rain1950(W. WA z8)

I agree. Unless plants were infected, diseased or had bug problems, just refresh it next spring and reuse.

    Bookmark   October 1, 2006 at 7:21PM
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tapla (mid-MI z5b-6a)

A slightly different perspective and why I hold it:

If the decision to reuse container soils is an economic one, who can disagree with the decision? If you aren't concerned about expense and are willing to go to some minimal extra effort to build a good soil, that is what I would elect to do.

Here's why: Container gardeners need to direct primary focus to insuring that the soil they are using will remain able to provide adequate air to roots for the expected life of the planting. Along with the ability of the soil to hold ample air, comes good gas exchange and drainage for rootage. All the other major cultural variables affecting growth are easily manipulated. Water, nutrients, sunlight, and to some degree, temperature can all be controlled easily. Aeration cannot and its consideration is as important as water and light to plant vitality.

The breakdown or collapse of soil structure occurs at an exponential rate. If we imagine the usable life of a peat based container soil from a bag, it deteriorates from a reasonably good soil when fresh to unusable after 2 years. It's not unreasonable to expect the soil to lose at least 20-25% of its air holding ability by the end of the first growing season. In the first half of the second growing season, it will lose about another 25% of its air holding ability and in the second half of the second year, near total collapse is likely as the remaining 50% is lost. Though this is an example of an imaginary soil, it is very close to what actually occurs. Another way of saying it is: Even though a soil might be performing acceptably at the end of the first growing season, you should expect a rapidly accelerating collapse in the subsequent year.

So, if you use a soil for 1 year and mix it 50/50 with a fresh, similar soil, 50% of the soil will have totally collapsed by the end of the growing season, and the other 50% will have lost about 25% of its ability to hold air. If a soil is not holding enough air, it's holding too much water. Water and air retention vary inversely in soils and when one increases, the other decreases. When soils hold too much water, you have to hope that the plant will use enough water or that enough water evaporates to prevent root rot issues and even minor cases of over-potting can mean terminal misfortune.

Additional considerations are 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 watering water. A slow soil will also have accumulated fertilizer salts and possibly insecticides that you may have applied and forgotten about last season.

I suggest that container soils be turned into the compost pile or garden and fresh soil used in its place unless monetary considerations prohibit.


    Bookmark   October 2, 2006 at 1:29AM
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treeskate(6a Hartford CT)

Thanks so much for all your advice! I think it would be best if I just put it out in the trash.....it seems a waste in one way, but based on tapla's description the decline in aeration and water retention doesn't make it worthwhile to keep it. I don't have a compost area.

It is just another area of gardening (and like many things to do around a house) that everyone tells you how to do it but no one tells you how to undo it.

    Bookmark   October 2, 2006 at 5:20AM
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With all due respect to Al, I also hold the theory that potting soil can be reused. The information he imparts is dead-on, however the impact on aeration, moisture retention and soil structure are not necessarily as pronounced as he describes nor do they necessarily occur over the course of a single season. I grow a lot of long term container plantings - those that remain intact for several growing seasons or even years before repotting - and with only a few instances has the soil "breaking down" (as it were) been a problem. And then it was more of a need to repot and root prune rather than the soil entirely. The same goes for more seasonal container plantings - reused potting soil, disease issues aside and refreshed as necessary, appears to offer the same exact features as entirely fresh material.

It all depends on the quality of the soil initially of course, but like many others, I reuse my potting soil after refreshing. Whatever works for you works :-)

    Bookmark   October 3, 2006 at 9:18AM
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I dont understand throwing soil away, if that is the way it is to be, How does one throw the soil away that was used in the garden after the crop is in. How deep do you dig and what do you replace it with. You just work the soil and replace the nutrants and plant. With my pots I just do what I think is right for the soil to make it like I think it should be to grow a good plant. WORKS FOR ME.

    Bookmark   October 3, 2006 at 5:11PM
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rhizo_1 (North AL) zone 7

Very nice, dangsr2, but we really aren't talking about garden soil but rather soil-less potting mediums. Garden soil and potting mediums are two different things, almost entirely!

    Bookmark   October 4, 2006 at 2:25PM
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rhizo I understand the difference in garden soil and potting soil, as I gardened in a garden for about 60 years and because of OLD health reasons I am in pots and buckets useing soil I make myself from a number of different things like ground oak leaves, mushroom compost, dry grass from the lawn, old pine sawdust, and anything I can compost to make something that looks and feels like soil. Now one thing I dont understand about soil in pots needing so much air to the roots. Some show photos of pots that are closed except the drain holes, how does the plant roots breathe. I have a lot to learn as I just finished my 2nd year in pots.

    Bookmark   October 4, 2006 at 4:28PM
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tapla (mid-MI z5b-6a)

... how do the plant roots breathe?

The primary force behind gas exchange at the roots is: each time you water, the water displaces soil gasses and pulls fresh air in behind it as it exits the pot and as it is used by the plant or evaporates. This is another reason that well-aerated and open soils promote healthy rootage. They need watering more frequently & as a result, offer better gas exchange.


    Bookmark   October 4, 2006 at 4:49PM
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I scatter mine around the flower bed otherwise it dries out and what I use it for the next year doesn't do well in it I've found. I hate to waste it.

    Bookmark   October 7, 2006 at 6:47PM
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Well here I go again on the soil subject, that soil I wrote about was remixed, fert. added and planted with collards and smooth leaf mustard, and I had just as good crop of greens as I have had in years. I did the same thing to the soil again and now I have some of the nicest tomato plants with blooms and small toms on them, as well as beautiful beans, corn, and cukes. all in my 3 year home made soil. I think I will stay with this soil and see how long I can use it and still get a nice garden.

    Bookmark   April 30, 2008 at 4:39PM
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Well here I go again on the soil subject, that soil I wrote about was remixed, fert. added and planted with collards and smooth leaf mustard, and I had just as good crop of greens as I have had in years.

Let me be brutally honest here. I think the results you are reporting are entirely accurate. Does using a well aerated mix make it much easier to grow vigorous, healthy plants than a heavy, collapsed mix? Of course.

Does it matter to the same degree for all plants? Nope.

What we are talking about here is the importance of oxygen at the root level and the danger of excessive water retention at root level (which displaces oxygen).

When growing veggies in containers (and rapid growing annuals in general) one isn't likely to notice the same degree of problem with a heavy, or collapsed mix as the grower with perennials, shrubs, trees, succulents or anything else with less vigorous roots.

The rules do not change. More oxygen to the roots=more vigorous plants.

The primary difference is that most veggies are so vigorously rooted that their roots will punch right through a perched water table and suck the water up removing the problems associated with a PWT. Most veggies are so vigorously rooted they will fully colonize a container in short order and make their own aeration passages around the roots reducing the problem of a 'tight' soil. They make their own way.

Does this mean it is ideal? Goodness no, it just means that there are plants that will outright die in a collapsed soil and there are other plants so vigorous and tolerant that they will appear to shrug off the problems of a low aeration soil.

If the plant is an annual grown for flowers or fruit this frees us from long term health considerations. It only need survive and do it's thing for a few months. Longer term the concerns increase exponentially.

It doesn't change the rules, it simply means that some plants (like annual veggies) will do fine with the rules ignored (to a point).

One can hunt high and low for a reputable source to say that oxygen to the roots is not important and not find one.

Some plants are just more tolerant of poor growing conditions than others and annual veggies that 'know' they have only a few months to grow and reproduce tend to be the most tolerant. What choice does nature give them? :)

Still, the rules remain intact. Better aeration at root level equals more vigorous growth.

    Bookmark   April 30, 2008 at 5:23PM
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calistoga_al ca 15 usda 9

I buy my mix from a commercial landscape supply who makes mixes for the nursery trade. Its organic matter is ground bark referred to as "forest products". A course sand and volcanic rock makes up the other major components. The soil I am able to reuse is from unsold or failed container plants. I do reuse it for selected containers, mostly 5 gallon and up. Preparing it for reuse I add one third fresh fir bark to make up for the break down of the original organic matter. Each container receives slow release fertilizer 18-6-12 at the rate of one teaspoon per gallon of mix. Regular applications of a liquid grow fertilizer are added during the season. Al

    Bookmark   May 1, 2008 at 9:51AM
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I like the way you explained the veggies growth and rootdevelopment justaguy. I always recycle most of my soil into tubs at the end of the year with a blend of 75% new. I do use more of the woody potting mix in my recycles though, almost 50% is medium sized bark 1" to 3" pieces. I have done this for the last three years and the veggies love it. This will be my first year with florals, so I may have to modify my thinking some. I will still use organics in 75%, and do side by side with Al's mix for the other 25%. I will not be keeping more than 4 or 5 plants (veggies) over to the next year, maybe more on florals. Thanks TiMo

    Bookmark   May 1, 2008 at 10:10AM
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