How to Improve Clay and Sandy Soils for Gardening

Dealing with Clay & Sandy Soils - Expert Advice

Q. I thought moving from cold Ohio to warm North Carolina would be great for gardening, but I have had a terrible time. We live a mile from the ocean and our soil is 100% sand. I add topsoil and manure every year and not even tomatoes grow very well. Could you recommend anything? I would like to keep it as natural as possible. Thanks,

---Karen in Cedar Point, NC

A. I'm not sure there is an unnatural answer for sandy soils, Karen! Anyway, you're on the right track, but with the wrong stuff. Your sand does need a bulking up with organic matter; but some kinds of manure are notorious for limiting the number of flowers and fruits because of their high nitrogen content (see this PREVIOUS QUESTION of the WEEK for more details). And 'topsoil' is a meaningless term for any dirt-like stuff they can load on a truck.

As you will soon read, the opposite of your sand—clay—drives gardeners crazy in the other direction. Your soil drains too well and doesn't hold nutrients; it's hard to keep plants fed and watered in such porous material. Clay holds lots of nutrients but doesn't give them up to plants easily; and the drainage is so bad its like growing in pots without any holes in the bottom.

The solution for your sand is a lot of compost. If you have a big garden, have a truckload delivered. And if you don't have them already, build raised beds so you can limit the compost to plantings and not waste it on walking areas. (See this PREVIOUS QUESTION of the WEEK for more details on raised beds.)

Rent a tiller and mix the compost in with your sand until the ground is about half and half. The result will be nutrient rich and hold more water, but still drain really well. Then cover the surface with an inch of compost alone and repeat this once or twice throughout the growing season. You need that much because your warm clime uses nutrients at twice the rate of your old Ohio garden; and you have a much longer growing season. And don't hesitate to use a nice non-wood mulch overtop the compost either; it'll help keep your soil from drying out too fast.

Q. Our climate is harsh (cold, windy and dry in the winter; hot, windy and dry in the summer) and gardening can be a real struggle. I started with "builders dirt" (mostly clay) and have succeeded with some trees and perennials, but not my lawn. I recently planted Bermuda grass to replace our tall fescue, which was dying from ever-increasing lack of water. I seeded and over seeded but the grass has not grown uniformly. How can I improve the soil beneath my lawn; and in my already planted perennial beds? Thanks,

---J. Squires; "in the very center of Kansas'

I used to listen to you in Delaware but I moved out to California and was hoping you could help anyways. I bought a house that needs a new back yard and I have clay soil. What is the best way to prep it for grass, flowers, fruit trees and a garden?

---Mike in Oakland

Most descriptions of perennials note that they require {quote} "well drained soil", which my clay is not. How does one make the soil better? Can you get rid of the clay?

---Jerrie in Leawood, Kansas

A. Yes; in fact there are two ways to get rid of clay, Jerrie: A backhoe for big jobs and a shovel for small ones. I'm not kidding. My only potential garden area was nothing but rocks and clay, so I removed the rocks, had a big load of compost delivered, tilled it in and built raised beds, hoping that the micro-organisms in that compost—and the many other loads applied over the years—would turn the clay into good soil.

It did not. Every year, I would dredge up big clumps of nasty stuff much lighter in color but heavier by weight than my enviable black compost. It was just like the rocks. I cleaned out EVERY rock when I started; where do all these new ones come from every year? Then I decided to treat those clumps LIKE the rocks and started chucking them into the woods. I find much less clay these days, and the actual chucking is as emotionally satisfying as the dispatching of slugs. (I still get plenty of new rocks, however.)

Now, if you go online, you'll find all sorts of advice on improving clay soils with things like gypsum or some mystical liquid. My guess is that these cures are as satisfying as the product you receive from a late light infomercial you couldn't resist. When you're starting a new garden, take the time to get rid of as much of the clay as you can. Have it dug up and hauled away. Curse and taunt it as it leaves on the truck. Throw things.

Then break up the clay at the bottom of that hole with garden forks, pry bars or small explosives, have a big load of half compost and half high-quality screened topsoil (that means nice and dark, not light brown in color) brought in, and garden (or establish a new lawn) in that perfect mix. Neighbors who previously laughed at your seemingly excessive response will soon be asking for the name and number of the backhoe operator when they see how your greenery thrives.

For already-established lawns, experts assure me that the soil underneath the turf will be slowly improved by regular compost feedings applied above. For cool-season lawns in the North, work an inch of compost into the grass in the Spring and an inch to an inch and a half in the Fall. For warm season lawns like your Bermuda (not necessarily the best choice for Kansas, by the way; I would have gone with a nice cool-season grass because of your winters), apply an inch of compost three times a year, evenly divided during the active summer growing season.

Pretty much the same for established perennials. Mulch them with an inch of compost every Spring; maybe another inch later on down South.

You can use liquid and granular organic fertilizers to feed plants growing in improved soil with expectations of great success; but stick to compost alone for the first several years if you didn't prepare the soil before planting.