Good soils are foundations for great gardens. Here’s how to prepare them in North Texas

Your landscape and gardens will be no better than the soils you prepare for them.

It’s not as glamorous a fall topic as migrating Monarchs and grow-your-own pumpkins, but “soils” need to be discussed, and there’s no better time than the fall. If you prepare your planting spaces now as things wind down for this season, the soil will “mellow” over the winter to be ready for a great start come spring. We gardeners can all use a little “mellow.”

Most likely you’ve been blessed with a clay soil. A sticky, gummy, icky black clay soil that gives you “big feet” when it rains and that becomes adobe-hard when it dries.

Believe it or not, that clay soil isn’t as bad as you might imagine. Clays hold moisture and nutrients because of their microscopic particle size. The problem is in getting water into them in the first place. Stay tuned for details.

Sandy soils, by comparison, are very porous, so it’s easy to cultivate them. You can literally plant with your hands. But rainfall runs through them, and nutrients leach out of them. Plants are soon wilted and hungry.

The best thing you can do to improve any kind of soil is to add organic matter. It comes in the form of compost, peat moss, rotted manure, finely ground pine bark mulch and shredded tree leaves. It’s the process of the organic matter’s decaying that allows it to break open clay soils. Organic matter helps sandy soils retain moisture and nutrients. So literally, one type of product solves all your soil problems. Really? That sounds more like what you’d hear from the mouth of a state fair barker.

The best approach is to add a blend of all kinds of organic matter. Once I have all the existing weeds and grass out of the way, I’ll rototill to 10 or 12 inches using a rear-tine tiller. Having tines behind the wheels results in a far better job of pulverizing the clay.

Next up, incorporate some of each of those sources of organic matter that I mentioned. I use two inches of sphagnum peat moss, then one inch each of well-rotted manure, finely ground pine bark mulch, and compost. Then I rototill a second time back to the same 10 or 12 inches to blend all the ingredients together. Oh, it’s making me anxious to get out there and plant right away!

If I am prepping what was a clay soil, I will also incorporate one inch of expanded shale soil amendment before that final tilling. Texas A&M research found that it did a better job of keeping clay soils “opened up” than sand ever did. Nurseries sell it. Ask for it simply as “expanded shale.”

Organic matter decays. It rots. Therefore, it also disappears. You must replenish it between crops by adding a couple of inches of new mix every year. Also, in the fall as I’m mowing and mulching tree leaves as they hit our lawn, I’ll put as much as a couple of inches of the shredded leaves into my soils and then rototill to include them.

Don’t do that in the spring — they need time to decay and blend in with the other sources of organic matter. That’s what a serious gardener might call letting his or her garden “mellow.” (There’s that word again!) Then when you till it again prior to the early spring plantings, the soil has a wonderfully soft feel to it. Sweet!

Should you add fertilizer to the soil as you’re doing this tilling in the fall? I don’t. That’s because nitrogen is the main element your garden plants will be needing come spring, and it’s water-soluble. As the garden lays fallow over the winter, nitrogen can leach out should we get generous rains.

My preference would be to use fall for my time of having the soil tested. The soil testing laboratory at Texas A&M in College Station gives very reliable tests. It was set up to aid farmers and commercial growers across Texas, but home gardeners also make use of the sophisticated equipment to get really accurate results.

Google the A&M Soil Testing Lab’s website and you can get full instructions for collecting and mailing your samples. They also show you the various tests they can run, but most homeowners will be interested primarily in nitrogen, phosphorus and potassium, plus pH (acidity/alkalinity) and soluble salts.

Most tests show soils to be very low in nitrogen because of its great solubility. It is quickly dissolved and utilized by the plants.

Phosphorus, middle number of the analysis, by comparison, is very slowly soluble. It can accumulate to harmful levels, so soil test recommendations often call for applying no phosphorus at all, perhaps for many years. Some states don’t even allow it to be included in fertilizers sold for large-scale application.

Potassium, the final number of the analysis, is present already in many Texas soils, so whether you add it or not isn’t a critical issue. Don’t go out of your way to do find it.

“Soluble salts” refer to mineral salts that are accumulating in your garden soils. Often, they can be from sodium. Some irrigation water contains relatively high levels of sodium. There are ways to address it, but that’s fodder for another story later.

Which plants deserve the best soil you have? I refer to that as those plants that justify “heroic” soil preparation, and I generally include in that list plants with shallow, less developed root systems. That would be vegetables and annual and perennial flowers. Also, groundcovers and low shrubs that grow to be three or four feet tall, for example dwarf yaupon or Carissa hollies or Japanese boxwoods.

Any plants that grow larger need to be satisfied with the soil I have natively. I simply cannot afford to be doing this extensive bed preparation for a plant whose root system is as big as a dump truck. I’ll water and feed them, but anything more involved than that — they’re on their own.