Clay-Packed Soil Needs Compost--Not Sand

QUESTION: Can you add sand to the soil if you have a heavy clay with poor drainage?

--M.K., Laguna Niguel

ANSWER: Adding sand to a clay soil is similar to adding sand to cement, a combination that makes concrete.

Clay is made up of tiny soil particles that cling together much as cement does.Concrete is about four or five parts sand to one part cement, and to keep a clay soil from turning into cement, you would need to add a lot of sand.

“The soil would have to be 80% to 90% sand to do any good,” said Garn Wallace of Wallace Laboratories in El Segundo, a soil consulting and testing firm.

According to Wallace, it’s much easier to use other means to improve a soil’s tilth and drainage. Perhaps the best method is to use a “green manure,” growing special kinds of plants that you then till into the soil so they compost. Although that method works fine on the farm, it is not a terribly practical, or speedy, approach in garden beds.

But adding homemade compost is almost as effective, which is why everyone should have a compost pile cooking in the backyard.

Other amendments are peat moss, mushroom compost or any of the various products made of ground bark and wood products that are sold by the bag at nurseries. Unfortunately, “these are almost like adding sand,” said Wallace, because you need to use a lot and they decompose so slowly.

Adding gypsum is always a good idea because gypsum replaces sodium in the soil with calcium and helps the soil “flocculate,” said Wallace, meaning that it binds the tiny cement-like clay particles into larger particles so the soil becomes more porous.

He suggests improving the tilth of a clay soil by tilling in gypsum and compost (or the next best material if you don’t have any), then begin growing plants (any kind) in the beds because they improve a soil as they grow. Do not rake up leaves and other debris, but let them become a mulch. As the leaves decay, earthworms will slowly drag additional humus down into the soil. It may take a few years, but the soil will become more manageable.

Crickets Usually Do More Good Than Harm

Q: You’ve written about other insects, but what about crickets? Are they beneficial? What do they eat?

A: There are several kinds of crickets living in the Los Angeles area, including one that is heard but seldom seen, one that gets in houses and one that would live in homes given the chance.

The most common, the several kinds of tree crickets, do feed on plant matter, but they are considered beneficial because they prefer to eat garden pests such as aphids, leaf hoppers and scales.

These are summer’s songsters, but you will almost never find them. What you’re looking for are thin, greenish and only half an inch long.

According to Charles Hogue, author of the excellent “Insects of the Los Angeles Basin” (Natural History Museum of Los Angeles County), “its voice, like that of a ventriloquist, is difficult to trace to its source.”

Easier to spot, though less common, are the chunky dark brown or black field crickets, because they often get inside houses and continue to sing. Usually they live under litter on the ground. They can become very minor pests if there are lots of them.

Another field cricket, the European house cricket, is light brown and smaller (three-quarters of an inch long). They were introduced from Europe, are often sold as fish bait or animal food and generally live in or around houses. I don’t know what they eat in the wild. Pet stores feed them cornmeal or raw potatoes and carrots.

Add Right Kind of Lime to Acidic Soil

Q: Believe it or not, I’ve been told that my soil is too acidic. They suggested I add lime, but what kind? There are several at nurseries.

A: That is surprising because most soils in California are alkaline. What you want to add is often sold as agricultural lime and contains calcium carbonate from ground oyster shells. I’m sure you were directed to add very little.

Don’t add Dolomite lime because it contains magnesium, which we already have in abundance in our soils.

And most people should never add lime to their soil unless a soil test has shown that it is acidic.