Soil for very large containers

9 years ago

I recently had a multitude of large planters built on my rooftop deck. The internal dimensions of the planters are 22" tall and 19" wide. Between all the planters, there is 53 feet of length to fill with soil. My plan is to do a garden of half boxwoods, and half lavender, with varying annuals filling out the rest.

The first 10-12 inches of the planter bottoms will be filled with upside down laundry baskets (cheap) with extra holes drilled, and with styrofoam packing peanuts. Finally, a weed fabric will be laid on top of the baskets/peanuts. The soil will start from the weed fabric and up. That leaves me with a total of 80 cubic feet of soil to source.

I've been researching Al's mix, and I wanted to know if the 5-1-1 is suitable for large containers like this as well. Obviously, part of the considerations in soil here is the economic cost, from both an initial investment of the soil to replenishment/replacement of the soil over time. I'm unsure if the gritty mix would be a better alternative, but 80 cubic feet of gritty soil mix is getting a little outside of my price range. The other alternative I'm considering if just a simple mix of perlite/compost/peat moss.

Also, I live in Chicago, and my roof does collect it's share of snow. Are there any considerations to take into place when snow on my plants/soil is melting?

Featured Answer

Nil13 usda:10a sunset:21 LA,CA (Mount Wash.)

9 years ago

If you use 5-1-1, you will eventually have to replace it. That of course necessitates getting the old stuff off the roof.

I usually specify an aggregate medium for roof decks if they are going to have perennials. The mix is typically 1 part pumice : 1 part DE (optisorb) or calcined clay (turface). Unfortunately, it is my understanding that pumice is hard to source in your area, so you might want to look for growstone.

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Comments (8)

jane__ny
9 years ago
I would use a potting soil, mixed with some small orchid bark or another small bark and perlite. The potting soil will hold some moisture during hot weather, drying winds and cold. Mix it about 1/3 each.

Thats what I would do and what I did for many years on a large deck. My plants grew well until they outgrew the containers.

Jane
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tapla (mid-Michigan, USDA z5b-6a)
9 years ago
Dubya - I would tend toward an aggregate mix as well, because of its longevity/structural stability. If you've been researching, you'll understand that a peaty mix/potting soil amended with some bark and perlite will be replete with issues, not the least of which will be a lack of structural integrity which would begin at the point of establishing the plantings and decline from there as the organic components do what organic components do - break down.

Al
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jane__ny
9 years ago
I would not recommend a stone based mix. It would be quite heavy and all plants need repotting eventually. Most of my large plants need to be potted up each year or two.

Furthermore, a stone based mix would dry out so quickly, I don't believe your plants would make it through the winter when the mix freezes.

Jane
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garyfla_gw
9 years ago
Hi

Here is the largest pot I ever attempted 3x3 foot commercial tree pot painted and made a dolly for it I had to use soil to the bottom for the bottle palm Thought it would never get full lol Used a mix or pine bark fines and top soil along with composted manure and some leca . I use it for winter annulas on the surface Palm is still doing well though I've had to add some mix over the years For one used in shade ,same mix but higher proportion of soils and no leca used empty soda bottles in lower third as I didn't need the depth for those . Keep in mind that these are not subjected to freeze ,have no idea what effect that would have?? . gary
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tapla (mid-Michigan, USDA z5b-6a)
9 years ago
An aggregate mix isn't inherently heavy unless it's made so. E.g., perlite could be a fraction of an aggregate mix, as could calcined DE, pumice, Turface, Haydite, ........ - none of which are particularly heavy. Neither is the point about drying out a valid one. Aggregate mixes can be made so they are very water retentive or so they hold little water.

Al
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jane__ny
9 years ago
Wow, Gary.

How large is that Palm?

Great growing!

Jane
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garyfla_gw
9 years ago
Jane

That bottle is the last of those I raised from seed from 1981!! lol It is still under 15 feet high but has a 20 foot spread lol Have given away all the others which are now all planted in the ground around the neighbohood

It had the largest caudex so kept it as a neighbor donated the pot and helped with transplant. I still feel 3x3 is WAY too big for a potted plant lol I did have the foresight to put it on casters

They are not hard to grow but the habit stinks lol Once the caudex starts they stop most vertical growth and gets wider averaging less then two fronds per year!! After 34 years it shows no sign of maturing !! The pot does provide a place for winter annuals .

Believe it or not there are palms that are evn slower!!! lol gary
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