Maintaining Soil Life in Containers - is it practical, or do we need to feed container plants?

[Susan BBPM]

NOTE: Whilst I personally am using no-dig approach to gardening, this question in relation to container gardening is specific to all methods that rely on 'feeding the soil' rather than 'fertiizing the plants'. So it also applies to chop and drop, green manure etc. Does 'feed the soil' work in a container where it's so easy for conditions to develop that kill off the soil life?

In my garden beds I use a no dig approach where you feed the soil life and in turn, IT feeds the plants. It works very well and it's easy. A 1 inch topping of garden compost once a year and the beds will grow as many crops as you can throw at them all season.

But I have very large patio areas where I need to use containers. Realistically, can you keep the soil life alive in a container? If you let it dry out briefly you'll kill off soil life. Too much heat, too much cold, too much water etc. Also, we keep hearing how important trees, shrubs etc and their root systems are to the soil life and thus to our plants - something that our container soil won't have access to.

How relevant is mycorrhizal network to veg growing (I know bacteria is more important to veg). But if it has any benefit at all to veg/annuals the moment you use a container you aren't going to fair as well as in garden beds

I get good results from my containers but I feed them all summer long with compost tea, worm tea, comfrey tea. I tend not to trust that the soil life will survive long enough in a container for me to treat it as I would a garden bed. I tend to empty out all but the biggest of pots and put in fresh potting soil each year.

Gardening in beds is a easy. You plant it and for the most part do nothing else until harvest time. But containers are hard work.

Or am I wrong in thinking that 'feeding the soil life' can't work just as well in containers?

 

[redback]

I don't use containers at all. The advantage of planting into the soil you find on your place is 'providence'. The flavor of wine comes from the unique soil that it grows in, and the bottle labels wax lyrical about the nuances of taste. Now I find that soil science has discovered microbial abundance around plant roots. This is new, enlightening and hard to imagine. So, I am trying to come to terms with this new underground network that is capable of growing plants without human input. Gardening in beds might be easier than in containers but it has plenty of challenges.

 

[cpp gardener]

Since container soils don't usually contain any actual soil and are primarily organic matter with 50% or less mineral particles (perlite, vermiculite, sand) there should be a quite adequate microbiome. Your various teas should give plants and micros sufficient nutrients to thrive. You could make your own potting soil with compost, most contain at least a little, and any other products normally included in potting soils and have a quite satisfactory growing medium. The need to replace or mix in additional materials yearly is due to the organic matter breaking down and reducing porosity, contributing to poor drainage. You also lose volume as the organics break down. If you make your own potting soil you can use more inorganic materials to better mimic real soil, but be careful to use lots of medium to large particles to retain volume. You would then just add your organics to the surface as usual.

 

[Susan BBPM]

Since container soils don't usually contain any actual soil and are primarily organic matter with 50% or less mineral particles (perlite, vermiculite, sand) there should be a quite adequate microbiome. Your various teas should give plants and micros sufficient nutrients to thrive. You could make your own potting soil with compost, most contain at least a little, and any other products normally included in potting soils and have a quite satisfactory growing medium. The need to replace or mix in additional materials yearly is due to the organic matter breaking down and reducing porosity, contributing to poor drainage. You also lose volume as the organics break down. If you make your own potting soil you can use more inorganic materials to better mimic real soil, but be careful to use lots of medium to large particles to retain volume. You would then just add your organics to the surface as usual.

I don't think I've expressed my question clearly enough.

To look at it another way - why is it that you can't use ordinary garden soil in containers?
(Typical answer to ttat is 'because the soil life in garden soil that areates it can't survive in a container environment'

And I'll follow that with a second question....

If you can't use garden soil in your containers, is it likely that methods used to feed soil life in garden soil (no dig, chop and drop, green manures) will work in containers over the long term?

 

[cpp gardener]

The problem with actual soil in containers is that drainage in anything other than sand is very slow and easily overwatered. You could use larger pieces of inert organics, like fir bark or coir, and coarse perlite or lava to improve the drainage.
I would think that you could do the permaculture processes but you may have to redo every few years to make up for decomposition and settling.

 

[DirtMechanic]

Second drainage. And drainage. Oh did I mention drainage? You will feed more frequently but more lightly because of good drainage too. Soil will pack and choke roots.

 

[Susan BBPM]

Second drainage. And drainage. Oh did I mention drainage? You will feed more frequently but more lightly because of good drainage too. Soil will pack and choke roots.

The problem with actual soil in containers is that drainage in anything other than sand is very slow and easily overwatered. You could use larger pieces of inert organics, like fir bark or coir, and coarse perlite or lava to improve the drainage.
I would think that you could do the permaculture processes but you may have to redo every few years to make up for decomposition and settling.

Why does water drain in garden beds but not in containers?

Obviously you both think there is something fundamentally different about the container that changes the characteristics of the soil contained in it?

Do you agree with me - that it's a less hopitable enviornment for soil life? It's the lack of soil life constantly working to areate the woil that leads to poor drainage? Or can you think of another possible explanation?

If it's down to soil life not thriving then 'feeding the soil' (with green manure or no dig practices of adding compost each year) won't work as there won't be enough soil life to make it worthwhile.

 

[Susan BBPM]

Another relevant snippit of info.

I read a study (I'll find the link later) that tested nutrient density in vegetables. They found that chemical fertilizers and organic slow release fertilizers both produced high levels of nutrients in vegetables. However, compost grown veg (without fertilizers) was low in nutrients.

So, based upon this, planting in containers with compost won't produce nutrient dense foods. It takes time for the compost to feed the soil life and produce food for your veg. But in a container there's a good chance of that soil life repeatedly being killed off by hostile conditions in the container (too wet, too dry, too hot etc). I also wonder if there's any benefit to putting manure into containers growing squash - does the benefit become available soon enough?

My interest here is in trying to figure out how best to use my containers. They are a necessity for me due to a large patio area (although I have garden beds too).

Is it worth trying to use some 'feed the soil' principles in containers, or is it best just to accept that you need to fertilize regularly and think of container soil as nothing more than a medium to hold water and nutrients? It's hard to find hard evidence - lots of evangelists for various approaches, and lots of compost selling businesses trying to convince us we need to buy their compost every year!

 

[roadrunner]

I don't like using containers because I have to water them too much. However, I do have a couple large containers and I treat them just like I do with my soil in the yard.

I filled them halfway with sticks/logs, branch cuttings and leaves (so I didn't have to dig up so much soil) and then put normal soil from my yard into the container.

I always practice chop and drop and occasional heavy mulching to keep level of soil up and I always have something growing in there, including "weeds".

This keeps the soil much better than any purchased garden "soil".

 

[Susan BBPM]

I don't like using containers because I have to water them too much. However, I do have a couple large containers and I treat them just like I do with my soil in the yard.

I filled them halfway with sticks/logs, branch cuttings and leaves (so I didn't have to dig up so much soil) and then put normal soil from my yard into the container.

I always practice chop and drop and occasional heavy mulching to keep level of soil up and I always have something growing in there, including "weeds".

This keeps the soil much better than any purchased garden "soil".

How large Roadrunner?

In my polytunnel I have a 12ft x 3ft x 2ft deep raised bed (essentially a large container). It's bottomless, but it's sitting on what was a hard, compacted gravel driveway. Like you, I filled it with old logs, cuttings etc then topped with compost. They are now on year 4 and I've used no dig methods with great success. I add an inch or so of compost each year after harvesting the last crop. I also put my worm farm on the bed in the winter so it gets a bit of help from the worm tea dripping in, but that's it. No fertilizer and each year I've grown new potatoes followed by tomatoes, cucumber, peppers. Nothing in it between October and Feb.

The tubs i'm undecided about are about 2 foot high and 18 inches at the top (tapering at the bottom). When I've tried doing tests the tubs filled with fresh potting compost each year do much better. It's too much work though.

I've tried cutting the bottom off of some containers and standing them on soil (to get the best of both worlds), but it doesn't really work well. I've found 2 years in a row that potatoes in beds and in pots on the patio in new compost do MUCH better than the bottomless tubs. Not sure why that would be. But bottomless tubs seems to be the WORST of both worlds! Maybe I'm not on top of the watering as much as I am with containers.

As a last resort I might end up lifting slabs on the patio and building a big raised bed. I have one spot in particular which is a fantastic sun trap - ideal for standing several large tubs of veg. But too much like hard work keeping them fed and watered. I think size might be key rather than contact with the soil.

 

[roadrunner]

How large Roadrunner?

In my polytunnel I have a 12ft x 3ft x 2ft deep raised bed (essentially a large container). It's bottomless, but it's sitting on what was a hard, compacted gravel driveway. Like you, I filled it with old logs, cuttings etc then topped with compost. They are now on year 4 and I've used no dig methods with great success. I add an inch or so of compost each year after harvesting the last crop. I also put my worm farm on the bed in the winter so it gets a bit of help from the worm tea dripping in, but that's it. No fertilizer and each year I've grown new potatoes followed by tomatoes, cucumber, peppers. Nothing in it between October and Feb.

The tubs i'm undecided about are about 2 foot high and 18 inches at the top (tapering at the bottom). When I've tried doing tests the tubs filled with fresh potting compost each year do much better. It's too much work though.

I've tried cutting the bottom off of some containers and standing them on soil (to get the best of both worlds), but it doesn't really work well. I've found 2 years in a row that potatoes in beds and in pots on the patio in new compost do MUCH better than the bottomless tubs. Not sure why that would be. But bottomless tubs seems to be the WORST of both worlds! Maybe I'm not on top of the watering as much as I am with containers.

As a last resort I might end up lifting slabs on the patio and building a big raised bed. I have one spot in particular which is a fantastic sun trap - ideal for standing several large tubs of veg. But too much like hard work keeping them fed and watered. I think size might be key rather than contact with the soil.

They are about 22-inches (56cm) in diameter by 17-inches (43cm) high.

 

[cpp gardener]

The drainage issue in containers vs open soil is that the containers have solid non-permeable sides and only one or a few holes in the bottom that create a perched water table and low aeration. As I said earlier, using coarse inorganic material like lava, grit, perlite and/or pumice will help keep the "soil" open and aerated while reducing "shrinkage" of the "soil" from organic decomposition. Conifer bark chunks, rice hulls and nut shells from pecans and walnuts also will work because they decompose very slowly. Adding any kind of compost or manure a couple of times a year will help feed the soil micro-organisms. If you add 25-30% inorganics at the same time it will help with the "shrinkage" issue, although eventually you may have a deep layer of the inorganics at the bottom with lots of organics at the top which creates a shallower and shallower "live" growing area. It probably can be done as no till, but balancing the organic/inorganic proportions could get tricky.
The issue with the bottomless pots is that darn perched water table decreasing drainage.

 

[skinyea]

I container grow every year. Tomatoes, Peppers, Okra, Beans. I used to dump the soil into the garden every year and start with fresh soil.

the Last few years I have been growing Crimson Clover and other clovers over the winter. I just cut them at the dirt level in the Spring, chop the roots up a bit and plant right into the soil. Have not changed out soil in 3 years and everything is growing well.

 

[Meadowlark]

Yes,yes Skinyea that's the way to do it.

I container grow every year. Tomatoes, Peppers, Okra, Beans. I used to dump the soil into the garden every year and start with fresh soil.

the Last few years I have been growing Crimson Clover and other clovers over the winter. I just cut them at the dirt level in the Spring, chop the roots up a bit and plant right into the soil. Have not changed out soil in 3 years and everything is growing well.

That stuff about not using garden soil in containers is perhaps the dumbest thing I've ever heard.

The thing I'm working on right now is determining how long it takes to replenish the garden soil in the container? 6 weeks? 12 weeks? or a full growing season with cover crop in place.

You have already proven replenishment can be done in situ using traditional techniques and I applaud you for that. applause! applause!

Now I'd like to know how long the replenishment requires.

I'm reaching the 6 week point with Sunn Hemp replenishing a potato growing container and anxious to get the results. I'm prepared to go 12 weeks and whatever necessary. I'm also going to try alfalfa and a run at crimson clover and also peas for the cover crop medium.

So much to learn but I love it.

 

[Susan BBPM]

I container grow every year. Tomatoes, Peppers, Okra, Beans. I used to dump the soil into the garden every year and start with fresh soil.

the Last few years I have been growing Crimson Clover and other clovers over the winter. I just cut them at the dirt level in the Spring, chop the roots up a bit and plant right into the soil. Have not changed out soil in 3 years and everything is growing well.

What size containers?

It just doesn't work well for me (except in very large containers). Things will grow, but they grow MUCH better when I fertilize with comfrey tea or compost tea. (OR if i put them in the ground).

So for example, I've got hubbard, butternut and acorn squash growing in various places in the garden. (In the ground, in a container with fresh compost and regular feed, and in a container that I'm treating the same way as garden beds). The winner is by far the squash in the container with fresh potting compost and feed. Second is in the ground. The container being treated like beds is trailing behind.

It works fine in a huge container (polytunnel raised bed 13 x 3 x 2 foot), but the smaller the container the quicker things go pearshaped.

CPP puts it down to poor drainage in a container, but I've never experienced drainage problems. For me it's drying out too quickly that's the problem.

We have unpredictable weather. Sometimes we have lots of rain and sometimes we have none for days (or weeks on occasion). So for example, you could automate watering but it would need to be something pretty sophisticated to work out when it last rained and whether any watering was needed. Sometimes you don't need to water a container for weeks on end because it rains so often, but then one day you suddenly notice it's dried out and the plant is wilting. The plant will recover with watering but I suspect a lot of damage is done to the soil life in the container. If you're regularly watering with comfry, compost or worm tea that keeps soil life boosted.

I mean, bottom line is that it doesn't work in my climate. My best guess is because it's too easy for the soil life to be killed off in a smaller container (probably due to drying out rather than waterlogging).

There are other factors I'm considering.

In garden beds you have the advantage of roots of other plants, mycorrhizal network etc.
You don't have this in containers, but if you're feeding with organic fertilizerson a regular basis it makes up for this weakness.
Take fertilizers out of the equation and suddenly you find that your container environment is lacking.