Square Foot Gardening Soil Mix…Do I think it works for Texas?

Apr 20, 2010

Well, some parts of it...

I get a ton of questions about SFG (Square Foot Gardening) so I thought I'd go ahead and address it here.  My opinion is No, you don't have to follow the principles to the letter to get the results you need, especially in our climate. Not to say that there aren't those who've have had success with the plan here.

I think that there are some good principles in the book that have obviously worked for the author in his particular experience. Specifically in learning how to rotate crops, spacing, etc., especially for beginner vegetable gardener.

However, In climates like those here in Texas, I do believe, from extensive experience, that you'll need to make some adjustments to the soil mix and the depth of the beds for best results. I just don't think the author has to garden in 107 degree heat!

Firstly, 6-inch deep beds are too shallow for my taste. Trying to keep your raised bed soil adequately watered is tough in the summer with that little soil volume. Especially considering that the organic matter is going to break down, leaving you with less than 6-inches worth of soil. Larger root systems, such as those of tomatoes, are going to need more soil volume. I build my beds to 12" tall.

I don't recommend tilling up the soil underneath your raised beds here, as you'll end up with lots of extra weed seed germination, Bermuda grass and nut sedge. So using newspaper and weed block fabric on top of the existing soil, without tilling it, is usually the easiest way to go. Watered cardboard works well too.  But that means you're going to need a good 8"-10" of soil to best accommodate your plants. 

More important is the soil mix. The SFG mix calls for a good amount of peat moss and vermiculite (The recipe is 1/3 blended compost, 1/3 peat moss, and 1/3 coarse vermiculite.) This can turn into a watering nightmare for you in the summer. Once peat dries it can be very difficult to rehydrate and you end up with a brick. You're much better off upping the levels of organic compost, humus, some high quality topsoil and expanded shale instead of the vermiculite. Throw in some greensand to help you retain moisture and provide micronutrients and some composted manure for a Nitrogen charge. If you want to use something with a peat moss-like texture, but without the hydration problems, go with COIR. A superior product in my experience (made from coconut husks).

Another thing...there is the impression in SFG that because you use compost in your beds that you don't have to use any fertilizer. Realize that compost is an organic amendment, which will eventually begin releasing nutrients slowly as it is decomposed by microbes (which will take a while to get going). Organic matter also breaks down faster in higher temps, so you'll have ot replenish more quickly in hot climantes. Also realize that what it will offer is mostly Nitrogen. It's not a complete "fertilizer" per say. You're still going to need to provide a good organic food to your plants, especially when first planted. Continual applications of compost will feed your plants as it breaks down, but don't expect a quick green up from it, and don't expect it to feed your plants enough if you don't have good microbial activity in the soil.

ADDENDUM: I realize there are folks on the SFG board who will tell you that you can't garden in the summer in Texas and that it's not our season, but they are wrong. They don't understand our climate and growing season, which is incredibly different even from areas just a couple of hours North of us. They also don't understand our soils. Please take my advice as a professional hortiulturist on this one. We have a 12-month gardening season here and you can grow year-round, NOT just September-May. But they are correct on one point, you can't garden in the official SFG soil here in July, because it turns to rock and you can never keep it hydrated because of it's composition and shallow depth. For example, you have to plant your fall tomatoes here in July. Period. if you don't you will not have a fall tomato harvest. Also, you're not wasting growing soil by going to 10-12" here - it's necessary. Sure, you can grow winter crops, such as lettuce, broccoli, etc, here in more shallow containers, but not larger warm season crops. Once you get some experience under your belt, you'll see the difference. You can't successfully harvest year-round here in 6" of soil, not to mention 6" of soil that is heavy on peat moss.

Here is one of my discussions on good soil mixes for your Texas raised beds.

There are 8 comments for this entry

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Apr 20, 2010
4:06 pm

I am now witnessing the impact of square foot gardening in my garden. Very intensive indeed, the french way. The approach forces the plants to live closely, touching one another and affecting growth in a positive way. As mentioned, fertilizing is too central to be neglected. It is a fair approach to be a little bit excessive in putting fertilizers, because plants are living like sardines in a can.

Cheers ....

Leslie Finical Halleck
Apr 20, 2010
4:11 pm

I grow very heavily planted mixed beds myself, although I don’t follow any sort of SFG plan. Us professionals tend be a bit more loose! Lol. If your soil is quality, you can grow lots of plant and get heavy production in very small spaces.

Topsoil supplier
Jan 31, 2011
2:56 pm

I have substituted shredded green waste for compost, and this seems to work fine to. My beds are also about 12 inches deep.

Feb 13, 2016
6:01 pm

Is there any benefit to building the beds deeper than 12” (like 16?”),


Feb 13, 2016
9:27 pm

Lelia, I find that unless you’re growing larger perennial plants you don’t need to build that deep. You’ll have to use more soil and it can mean consistent moisture management challenges. Perennial asparagus plants would be happy in a deeper bed- very long varieties of carrots…but you’ll find most edibles have fairly small root systems and deeper beds aren’t necessary.

Mar 30, 2016
7:49 pm

I mixed compost, peat humus, a little vermiculite and perlite all together in my garden. I was trying to do a square foot garden 1/3 each mixture.  However, I didn’t realize that peat moss and peat humus aren’t the same thing.  I live in Texas on the gulf coast. Most of my plants seem to be doing ok, but my some of them are yellowing (zuchini, yellow squash, a few herbs). They are only a few inches tall each and aren’t growing, just yellowing. They seem to be yellowing from the small leaves to the big leaves. Even my pole bean leaves are no longer dark green. - what can I do to fix the garden? I saw that you said more humus is better, but I’m still worried I don’t have enough drainage. I put a little fertilizer on it today in case it’s nitrogen.

Thank you for your advice!!

Leslie Halleck
Apr 01, 2016
7:59 am

Hi Danielle, Remember is that “new” soil may not be very bioactive. Not enough beneficial microbes to start breaking down the organic matter in the compost to support your new plantings with the nutrients they need. It can take 6-months to a year for your beds to “season”. Use a fertilizer more often initially to prevent nitrogen deficiencies.

Humus is highly decomposed plant matter - while more nutrient dense than compost, you’ll still need to fertilize. By combining mostly compost and humus, with a bit of peat moss, you’ve planted in an almost 100% organic mixture. You’ll should get some stable mineral soil structure added in. Look for some high quality top soil (I love Soil Menders) and add about 1/3-1/2 to your beds.

Add biostimulant (Espoma has a good bio-starter) to feed the microbes. Try a shot of a liquid organic foliar feed for a quick boost to you plants (I love Hasta-Gro). Then, be sure to add a good granular vegetable fertilizer into the soil.  Organic composted manures are great for veggies. I like to throw in dry chicken manure from my flock - it not only is high in nitrogen, but it’s a mega jump start for the beneficial soil microbes!

Braden Bills
Jun 06, 2017
8:26 am

I’m trying to decide if gardening soil mix would be good for my garden. If it can work for most of the year in Texas, then it should be able to work in my climate all year round, save for winter! I live in a much more temperate place, after all.

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