Building Container Soil

[Mark Anderson]

This summer will be the 5th year for my rooftop container garden. Last summer we had a pretty bad drought here in Chicago which I think exasperated some mistakes I have been making with regards to my soil recipes. So now looking forward to Spring I'm researching on how to build container soils and its getting so confusing I feel like my head is about to explode. Some say add sand for drainage but sand clogs macro and micro pores. Other sites say you need good drainage but your containers also need to retain water -- two completely opposite requirements. Some say use compost in your mixture others say compost does no good and micro-organisms in your container soil is not a good thing.

So the more I read about container soils the less I know and the now I'm completely confused. It now amazes me how anything grew in my garden these last 4 years because I've been doing everything wrong.

I want to keep things simple so I found this one recipe that I might use this summer:

1 part top soil 1 part peat 1 part perlite

That seems like a lot of perlite but I suppose it helps in aeration. There's a nursery by me that sells perlite in 3 cu. ft. bags for not that much so that's not a big deal. But even the potting soils I see in the stores never have this much perlite. I'm also considering using pine bark but am a little concerned about having woody stuff in the soil. I thought wood leeches nitrogen. Last summer I used building sand in my soil mix and apparently that was a *big* mistake. Although I had a good pepper and cuke crop, my tomatoes didn't do so well even though I watered them every day.

Does anyone have good (hopefully simple) recipes using material that can be purchased at Home Depot or preferably Menards?

Is it bad to use compost in the soil for veggies? I read last year that growing tomatoes in a container requires about 1/3 compost and that's what I used last summer but now I'm reading that using compost is not good. Compost supposedly breaks down the soil, reduces aeration, and increases water retention leading to root rot. I suppose everything is a tradeoff but some of these sites use absolutes.

I'll be digging out all my containers and recycling the soil as the top soil component in any recipe. Some sites say not to use this recycled soil because its broken down and get fresh soil. But how can this soil, after I break it up in the soil mixing box, be any worse than those bags of dirt that you get from Menards? How do I know if the Menards soil isn't broken down either?

Also if anyone has good links to soil recipes that would be good too. Thanks for any help.

[Timothy]

Good day Mark, Here's the recipe for potting soil out of my MG manual.

1 part garden soil (not clay)

1 part washed builder's sand, perlite or pumice

1 part peat moss

1 quart of steamed bonemeal per bushel (8 gallons) of mixture

1 pint of dolomitic lime per bushel of mixture.

When I've made this, I mixed it and stored it in a 32 gallon garbage can with a sealing lid. To help with moisture issues that you may have, add some form of hydrogel, better know as soilmoist, to your high water using plants such as your tomatos. In a perfect world, a drip irrigation system on a timer would be best but hydrogel is a good alternative. I use a lot of the stuff every year on my clients' hanging baskets. With out the hyrogel, the baskets would need watering 2 or 3 times a day.

I would recommend against recycling the old soil in the containers and re-using it in new containers. The old soil will very likely have salt build up in it and can also contain diseases. The store bought soil _should_ be fresh and un-used with no salt traces in it.

If you have access to a pick-up truck, I'd suggest that you go and by a yard of fresh top soil. A yard of high quality soils cost 16 dollars around here and is much cheaper than soil by the bag. Good luck.

[sherwindu]

Hi Mark, I'm a neighbor of yours just north of Chicago. I don't know where you are getting your information, but some of it sound suspect. I use the coarse sand in my raised beds and containers. Used in moderation, I think it's effect is contributory. It prevents topsoil from caking up and assists in drainage. It's hard to recommend a single size that fits all, in this case. Different vegetables have their own requirements for soil composition, ph, etc. I don't fret about this too much. It's more important that your containers do not dry out in the summer sun. I have been using less peat now than in the past, because it tends to made my soil too acidic. It is good for very heavy clay soil, which is only a problem for our region if you dig down about a foot in my yard. I don't know where you heard bad things about compost. It can only be a problem if it is not fully processed, which in that case it will leach out nitrogen from the soil. It is very useful to spread around the top of your plants to keep them from drying out in the sun. Perlite is good for starting plants and has less potential for containing diseases, but I would not use it for long term growing for containers growing veggies outside.

Mark wrote: This summer will be the 5th year for my rooftop container garden. Last summer we had a pretty bad drought here in Chicago which I think exasperated some mistakes I have been making with regards to my soil recipes. So now looking forward to Spring I'm researching on how to build container soils and its getting so confusing I feel like my head is about to explode. Some say add sand for drainage but sand clogs macro and micro pores.

I'm not sure what pores you are talking about. For proper drainage in a container, you should put stones over the holes in the bottom so that the soil mix does not block these up.

Other sites say you need good drainage but your containers also need to retain water -- two completely opposite requirements.

Retaining water is not the same as drowning the roots. Just keep the roots moist is your best guideline.

Some say use compost in your mixture others say compost does no good and micro-organisms in your container soil is not a good thing.

I have been getting good results using compost both in my containers. Microorganisms are not necessarily bad for growing things. You have them inside your stomach helping to digest your food.

There can be dozens of other reasons why the tomatoes didn't do well. If you don't go overboard on the sand, you tomatoes should do fine, and will benefit by the soil not clumping up.

You can't buy good compost at these stores, nor can you buy the coarse sand there, as well. You also cannot buy real manure there. You can use manure if you place it at the bottom of the pot out of direct contact with the roots, or mix it very thinly throughout your mix.

definitely not.

I don't know where you are reading these things, but using 'fully cooked'

compost as I explained, will be of great benefit. You only get root rot if you overwater, or block the drainage somehow by using pots with inadequate

drainage. There is a much greater danger of roots drying out than drowning, in most containers outdoors in the sun.

I don't know what you mean by broken down soil? Soil does not 'wear out'. It might lose nutrients, if you don't replace whatever you take out. Unless your soil contains some pathogen, it's probably ok to re-cycle. You may want to amend it, depending on what is needed.

Never hurts to research this, but I think you are putting too much emphasis on this soil thing. Don't hesitate to add compost and sand to your mixtures. Proper watering, good seeds, and sufficient sunlight are much bigger factors in successful vegetable growing.

Sherwin D.

[Dwayne]

Before you decide to add lime or not, determine what pH needs you have to raise what you are planting. Lime will raise the pH, as will watering with hard water. Most good plants require an acidic soil to produce well. If you get the pH too high, the only thing that will grow in it is weeds. I would suggest a pH of between 6 and 6.5 unless you are going to raise blueberries or other plants requiring more acid, and then get it down to around 5.

Dwayne

[presley]

Maybe this only works in my climate, but I don't change my soil in my large

[Mr. Bill]

I use (and have for many many years without problems of any sort):

1 part pine bark soil conditioner 1 part organic humus 1 part top soil 1 tablespoon per 2 gallon container garden tone organic fertilizer

No sand (the topsoil around here tends to be very sandy in and of itself).

I have been using this mixture for fourteen years now and even in times of severe drought it retains moisture quite well and will not cake. I water when the top inch of soil feels dry to the touch. The trick is to keep the container shaded so it does not build up heat and cook the roots while drying out the soil. The only thing I have had marginal success (instead of good success) with is the tomato, though sweet 100 did very well, other tomatoes did not.

Bulbs seem to love it!

Mr. Bill

[WeeWilly]

I've had the same question. We are "blessed" with clay soil here in most of Calif. I'd like to build some raised bed gardens but can't get over the cost of not only building the structure.. but mainly filling the beds. If I build six beds that are 4'x10'x12" I'm looking at about 40 cubic feet of material per bed if I dig some of the material down into the local soil. This times, let's say 5 beds is 240 cubic feet or about 9 yards..

Anyone know a way to reduce the overall cost of the soil? Might be a dumb question.. but thanks for bearing with me.

Bill

[Dwayne]

Find a building contractor that is going to have to get rid of a lot of dirt, and see if he can help you. Get it piled near your home and amend it to your needs before putting it in your garden area.

Dwayne

[David E. Ross]

See my recipe for home-made potting mix at . This requires no pH adjustments (lime or sulfur) for most plants.

If you can't get a small amount of compost from a friend, use topsoil where something was actually growing. You need only a small amount, just enough to supply the beneficial soil bacteria that will release the nutrients from the bone meal, etc. In a gallon of mix, I might use only a handful of compost. With only a small amount of compost or topsoil, local variations in texture and pH have little effect on the mix.

This mix will drain very well. But it will also remain moist. Yes, it is moist without ever being soggy (unless the container does not have a drain hole or is sitting in water). Unlike many mixes, the moisture remains available to plant roots until the mix is almost totally dry. In other mixes, existing moisture gradually becomes unavailable as they dry.

In any case, either use a porous container that allows moisture to escape through the sides and thus stay cool, put the container where it is in the shade while the plants get sun, or put the container inside another container. Many container-grown plants fail in the summer because the roots cook. No amount of moisture can prevent this.

[Tex John]

Collect up bags and bags of leaves from peoples trash and compost them in place. Taks a few months but the price is right!

John

[simy1]

To you:

the best way to fill a new bed for free is to have a tree service dump

200 cubic feet of wood chips on your front lawn. They will do it for free.Once in the beds, it will take a couple of years to both decompose and mix perfectly. The earthworms will do the mixing for you and initially you will be limited to crops that like clay topped with partially decomposed wood chips (things like tomato or potato or garlic). Wood chips produce excellent humus when they are done. You can speed up their decomposition by dumping N-rich organic matter on top of the chips, of which the best is kitchen scraps. Manure is not seed-free, whereas the chips are, so it is best to avoid contamination and hold the manure until weeds come in on their own three years later.

To the original poster:

1) garden soil does not mean much. In my back yard, garden soil is 90% sand. Your garden soil might be 80% clay.

2) different crops react differently to high levels of compost. Tomatoes, radicchio, garlic, melons and squash, potatoes, all love to grow directly in the compost pile. So for those go ahead and use pure compost. Other crops prefer a fine, neutral, settled soil, things like cabbage and onions and okra for example, for maximum performance. Lettuce will grow in unfinished compost so long as it is neutral (leaves-dominated).

3) Then you have to figure out the root system. Most melons have a taproot and they might not be happy in a container. Same for carrots and parsnips.

4) finally, some crops do just fine in waterlogged soil, but things like garlic or melons or beans will not accept it. Melons will tolerate some drought if they have a fully developed taproot. Others, like cardoon and many greens, will rather be too wet than too dry.

so go ahead experiment and change what does not work. You can't have just one soil for all plants.

[Mr. Bill]

Just a big HUH? Compost "breaks down the soil"??? Maybe you read that one wrong or maybe it was not punctuated or worded correctly. That passage probably should have read 'breaks down IN the soil. Coarse compost (with the possible exception of worm compost) will not impede aeration in a soil mix. The 'micro-organisms' in compost are not "bad", there are going to be micro-organisms even in a soilless mix. Compost will aid in water retention, true. Too much of anything can be bad but the quoted paragraphs make compost sound like arsenic!

Mr. Bill

[RobinM]

Hi

Though northern Virginia has the dreaded clay soil, I was surprised when I moved into my current house and found that it's built on what used to be an old river bed. My soil is mostly sand and gravel, with "gravel" up to the size of baking potatoes. Raised beds it had to be. The guy who tried to till me a garden with a rear-tine tiller made beautiful spark showers on the rocks.

I made 4 raised beds, using 2" x 10" X 8' boards. The beds are 4' x

8'. Going on the instructions of a book called "Cubed Foot Gardening", I plopped the frames down on my yard grass and filled them up. What I used was a mix that my local topsoil company makes that's regular clay topsoil mixed with leaf mulch. I mixed this with additional composted leaf mulch at about 2/3 topsoil mix to 1/3 leaf mulch and filled the beds up. I didn't dig it in, didn't bother to kill the grass, or anything like that. I DID need to add a bit of nitrogen the first year, since I used so much leaf mulch to begin with, but that was the only deficiency noted. For the 4 beds, I spent about $150 for the soil, which was about 5 cubic yards, if I remember correctly. (3 of the mix, 2 of leaf mulch) They were filled to about 1" from the top. I had a wonderful harvest the first year. Zucchini, tomatoes, chiles, eggplant, beans, cucumbers. (Made 52 pints of bread and butter pickles, in addition to the cucumbers we ate fresh!) After the first year, I got another yard of leaf mulch that I mixed in and things grew great the second year, also. The beds are FULL of earthworms during the summer.

I was just out on Saturday doing some clearing of weeds and leaves. The soil is gorgeous black stuff. In the next day or so, I'll be putting down black plastic on one bed to warm the soil a bit, then removing that and planting lettuce, radishes, beets, and broccoli raab under tunnels. Come spring, I'll be putting in 2 more beds, both 6' x

20' x 10", one for corn and one for tomatoes. They'll be filled with the same stuff. As far as I'm concerned, you don't need to dig the raised bed soil into the ground soil, and 10" beds are plenty deep enough. Let the passage of ground insects and worms meld the two, and let the sod decompose to add to the organic material.

YMMV

Robin Alexandria, VA

[WeeWilly]

Thanks David.. all good info.. actually, these will be rather large redwood containers.. likely 4 feet x 10 feet x 12 inches

Bill

[Dwayne]

Can you get cedar? Termites wont bother it like they will almost everything else I know about.

Dwayne

[WeeWilly]

Dwayne.. probably.. but, I'll probably use redwood.. it's local.. It's the soil in the box I'm concerned with..

[Mark Anderson]

I'm also on the North side of Chicago. Where do you get this coarse sand everyone mentions? Last summer I used sandbox sand which I now find out was not the right ingredient. I only used it because I needed to get rid of it -- and the drought last summer exasperated this mistake. I did read many recipes calling for this coarse sand though. My favorite nursery around here is that Farmer's Market on 4500 N Elston but since it's winter I'm not sure if they're even open to go shopping for this stuff.

I read that compost clogs macropores reducing the drainage capability of the container. It was also mentioned that micro-organisms, although beneficial for non-container gardens, can be harmful in a container environment. This is why I'm confused because there are so many different scientific explanations proposing opposite solutions. I would prefer to use compost in the veggie containers. Farmer's Market sells bags of Mushroom compost that has a lot of texture which would seem to help improve the soil structure. I'm not sure, however, how much nitrogen this compost leeches since it looks like it might be under decomposed.

My veggies are on the main rooftop so they get sunrise to sunset sun in the summer. It's encouraging that the soil isn't the biggest factor and maybe I just need to make small adjustments to my mix. As others have pointed out in this thread, I think my tomato problems might have been due to root burn. I use 20 gallon plastic tubs (with holes cut for drainage) and it does get pretty hot up there. This summer, along with a different soil mix, I'm going to build something to shade the soil and the pots from getting hit with direct sunlight.

[Mark Anderson]

I'm just quoting what I read on that Gardenweb site. I have always used compost in my mix and have read that veggies, especially tomatoes, require a layer of compost in the container to grow right. I guess the non-compost people suggest that all the nutrients in a container garden should come from fertilization. I also need to become more familiar with fertilization since I don't think I do that correctly either. I usually buy those Miracle Grow packets you mix with water and every plant but the tomatoes get the same feeding. The tomatoes get the special Miracle Grow tomato mix.

[David E. Ross]

Mark Anderson wrote [in part]:

I use washed plaster sand. This is a coarse sand you should be able to get at any building materials yard (not Home Depot or a lumber yard, but a place where you would buy rebar, bricks, concrete blocks, gravel, etc).

You don't wash it yourself. "Washed" means that the sand was processed (often near the quarry) to remove silt, mud, and debris. This is a clean sand, suitable for making a good quality of stucco.

[frogfog]

what if one lives in an area where there are no deciduous trees = only junipers and spruce trees....what would you recommend then?