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when you need lots of potting soil...

Posted by irun5k St Pete, FL (My Page) on
Sun, Sep 9, 12 at 15:06

Hello all,

I grow various things like plumeria and fruit trees. Since I have limited room for in-ground planting, large planters are of interest.... I'm beginning to consider larger pots (maybe > 15 gallon? for some reason pots are not labeled in terms of the volume they hold.)

In all my smaller pots I've made the gritty mix. In a perfect world I suppose I would use this in very large pots also, but I simply cannot manufacture it in those quantities and it would also be quite expensive. In fact, even something like MG cactus mix is an expensive option considering it is only sold around here in tiny bags at $4 a pop.

What do you guys use when you need to fill a huge pot? I'm guessing it might be more cost efficient to buy a couple of materials in bulk and assemble my own but I'm curious what you guys do.


Follow-Up Postings:

RE: when you need lots of potting soil...

Get bags of mulch and make a 85% pine bark and 15% potting soil mix. Add some lime and let it sit a week or so. Make sure to fertilize.

I have tryed this mix and it works great. I get a lot of pine bark left over from making the 511 so I use it to make that mix. If yo ucan find pre sifted pine fines in the up to 1/2" then you should make the 511.

They are fruit trees so you really need a fast draining, long lasting mix.

Otherwise, my fast lived annuals durring the summer I even used potting mix/ peatmoss.

I would still rather try a bark based mix even for my annuals because I can reuse the soil a few years if it is bark based so really I am saving in the long run, and plant health is higher.

RE: when you need lots of potting soil...

  • Posted by tapla z5b-6a mid-MI (My Page) on
    Sun, Sep 9, 12 at 16:29

Brian - I use the 5:1:1 mix for a lot of plants I intend to be in the soil for only 1-2 growth cycles. When made, the soil ends up costing about half what most bagged mixes cost, on a volume:volume basis, and offers much greater promise that the plant will be able to grow substantially closer to its genetic potential than if it was in a heavier, more water-retentive mix. Though it doesn't offer the aeration and reduction in ht of the PWT that the gritty mix does, it does offer a little more water retention than the gritty mix and far greater aeration and structural stability than commercially prepared, peat-based mixes. For plants that need repotting frequently or are what you would consider short-term plantings (like veggies/annuals) it's not much of a compromise, but the savings is notable.

The concept explained in what I'll link you to are much more valuable than the recipes, even though the recipes are the best way I've found to implement the concept to date.


Here is a link that might be useful: You'll see what he means if you click me ..,..

RE: when you need lots of potting soil...

When I needed to fill 100 gallon tree tubs for my moringa trees, I just ordered 3 yards of crushed pine bark, along with some other things I needed at the time. I knew that this particular bark was extremely well ground... a local nursery told me that they use it as their source for grower mix and I had gone to see it myself.

I used it directly in the containers, mixed with perlite, with no screening at all. The only caveat is that I fertilized extra heavily at first to counteract the potential for nitrogen tie up from uncomposted bark. Calcium nitrate was really helpful for this.

RE: when you need lots of potting soil...

I cant say that the 85% bark and 15% potting mix is best. It has bark from 1/2-1" and potting mix. I just dont want to give any wrong advice. Where the recipe worked for me, it may not work for others. The 511 is a trusted mix. I also read else where is is good to keep the largest particle size 3/8" in a good mix.

RE: when you need lots of potting soil...

  • Posted by irun5k St. Pete, FL (My Page) on
    Sun, Sep 9, 12 at 22:15

Thanks for the responses so far. It does sound like some "build your own mix", e.g. the 5-1-1 or a variant, may be the way to go.

At FL theme parks, I often see large plants/trees in huge planters, probably 50-100 gallon. Some of them, I believe, are permanent installations. I can't imagine that they remove the contents of each planter every year or two and freshen up the soil? I wonder what soil/mix they use? I'd love to befriend the head gardener at one of these places and learn the tricks of the trade.

RE: when you need lots of potting soil...

They use 3/4" gravel. Something that will never break down.

RE: when you need lots of potting soil...

Brian, I buy a metre of the best garden soil from our local supplier and mix it with half a metre of washed co arse sand or fine scoria.The garden soil is a mixture of loam, sandy soil,mushroom compost and composted mulch in equal quantities. When filling the pots (mostly 5 gallon but some larger) I add some sheep manure or my own compost. After harvest, I mix in some more sheep manure or compost before planting the next crop. While the plants are growing actively, some granular fertilizer or urine helps them along.
The potting compost lasts several seasons but the plants are rotated. As all the roots are left in the soil, the soil improves with each planting.
My experience is that when using a soil based potting mixture a proportion of one third coarse washed sand is esential. Fine scoria (laterite) seems a better alternative to sand although laterite can be alkaline. Mike

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