Suggestions for soil prep for Georgia clay soils?

[Henrius]

I am planning a desert garden in my office courtyard. So far, the Agaves have done very well.

Now I want to plant some cacti species. The small courtyard is flat, with not much chance of terracing the soil. Georgia is wet in winters, and famous for its heavy red clay soil! It can rain several days at a time in any season, and the soil can quickly waterlog.

My plan is to dig holes about 7 inches deep when I want to plant a specimen, fill at least half the depth with gravel, and then use a mix of 50% potting soil and 50% coarse sand around the plant. I figure this will drain any rainwater at least below the level of the plants fairly quickly.

Anyone else got any better tricks for making Cacti survive? Architecturally, there is not chance of erecting any sort of cover to shelter the plants from rain in winter.

[adetheproducer]

Make raised beds so if the ground does get waterlogged the more corse planting material can still drain out if the sides of the bed rather than straight down. If you just dig holes you are just making a sealed bottom pot then putting it bellow the growd level.

[A. Dean Stock]

I second that advice. Digging holes will just make it worse. In areas where I have more clay than sand, I've also had to go to raised beds and the use of lots of gravel in the beds in place of sand. It would seem that sand would drain water well but it doesn't. You need a lot of rock and gravel in the raised beds and go easy on the sand. Beds should be raised at least 2 feet but 3 feet would be better. Even then, in your climate you might get some water damage without a cover to keep out some of the rain. This depends a lot on what you plan to grow. If you cannot put in a raised bed, you might try removing the soil down to at least two feet and replacing it with gravel and rock.
Dean

[cactushobbyman]

I have heavy clay soil, but way less rain. My beds have some slope so the rain will run off, but the soil remains wet all winter. I do dig holes and back fill with gravel. In my area we hardly ever get more than an inch of rain in a 24 hour period and in our area our wettest month max is 3-4 inches total. In your area I'm guessing you get more rain in one day that we get all month. I would raise your beds with slope so the rain will run off and use what other have suggested and look for plants that like a little more water than others.

[Saxicola]

I also fully agree with the raised bed idea. If you must keep it at ground level there the only fix I can think of for the issue Dean mentions is installing a french drain.

[Henrius]

Thanks for the help, guys. Building a raised bed is still a problem because I would be piling soil against stucco, and there is wood framing underneath the stucco.

The big news is to use gravel in the soil mix instead of sand. What size gravel? The tiny size used in aquariums, or the regular size used in mixing concrete?

Kim

[A. Dean Stock]

I don't think the small stuff would do you any good. I'd use construction gravel from a source with more rock than sand or soil and low in clay. I think that the suggestion to use a "French Drain" is also a good bet if it is possible to integrate one in your situation.
Dean

[Henrius]

Thanks Dr. Stock. I planted an Enchinocereus today using a modified method. I dug the hole much deeper, about 14 inches. I filled it to within 3 inches of the top with gravel, making a sort of mini French drain. Then I filled to the top of the hole and a little above with a very porous soil mix, with a little gravel mixed in. Then i surrounded the plant base with gravel to keep it dry. Even the heaviest rain would percolate at least to the level of the top of the underground gravel, and never would the roots be waterlogged.

We will see if this works with my new plantings. Strange how the Agave roots do not seem to mind soggy soil. I have never lost an Agave by overmoist soil.

[Henrius]

I also fully agree with the raised bed idea. If you must keep it at ground level there the only fix I can think of for the issue Dean mentions is installing a french drain.

You have quite a good selection of plants on E-Bay. Which ones are the most frost and excess-water resistant for use outside?

I am also looking to replace a Euphoriba obese male-female matched pair I had for years, that I used to cross pollinate to produce fruit. If you have any sexed plants of that species, let me know! Henrius@mindspring.com

[A. Dean Stock]

Your success with Agave vs cacti is the opposite of my experience. I'm in a very dry area and killed several Agave before I finally learned that Yucca and Agave are not cacti and need much more water to do well.
Dean

[Saxicola]

Thanks Henrius! Let me get back to you about what I have that might do well in your area (I'll PM or email you). Unfortunately much of what I carry are plants that wouldn't handle a hard frost, but I've got a few things I think (and I can get more fairly easily). As for the Euphorbia's I know I have a few female ones that aren't listed. Let me check and see if I have any confirmed males. If not I can probably get one within the next month or so.

-Kyle