(This article was first published in The Gateway Gardener September 2006 issue.)

By Robert Weaver

If your garden or lawn isn’t performing up to expectations, it’s a dirty little secret that most problems begin with the soil. Well, you’re in luck, because fall is a great time to improve soil in existing gardens, create new beds for planting next spring, and give  turfgrass lawns a boost with a topdressing of fresh organic matter.

Clay—It Gets By With A Little Help From Friends!

Gateway gardeners lament much about gardening in this region—the cold winters and hot summers, humidity and drought—but heading their list is often the clay soil beneath our feet. But clay actually has some redeeming qualities for garden plants. It holds moisture and nutrients in the root zone (sometimes too well), and gives roots a firm basis to support plants. Plants native to clay soil regions grow quite well in it without any assistance from us.

Unfortunately, we gardeners get bored with those plants, and want to introduce to our gardens other plants that don’t do so well in heavy clay soils. They get root rot because the soil doesn’t drain well, or grow poorly because roots can’t penetrate the dense clay. That’s when we need to start tinkering with the basic structure and texture of clay, adding amendments to ease compaction, improve aeration and drainage, and add organic matter.  There are a multitude of products to help you achieve this. Here is a short rundown.

Bulk Soils, Compost and Mixes

For the big jobs, such as creating a new bed or amending large beds, you’ll probably want to have product delivered in bulk. The main bulk source in our area are the St. Louis Composting locations in Valley Park, Millstadt and their Organic Resource Management, Inc. (ORMI) location in Florissant.

St. Louis Composting has several soil and compost mixes for gardeners. Soil products include straight topsoil, a mix of 70% topsoil and 30% compost recommended for sod installations and garden use, a Garden Mix of 50% river-bottom topsoil and 50% compost (a popular choice for raised beds and amending heavy clay areas) and their SLC Mix, a blend of topsoil, composted manure and compost, ideal for roses and perennials. They also offer various blends of compost and composted manure for gardeners who want to amend existing soils or topdress lawns without adding more topsoil.

By the Bag

For smaller jobs, or to amend your soils more precisely with specific products, it’s more convenient for most homeowners to bag it! Here are some popular and helpful products to help you turn your clay soil into loose, rich, productive garden soil. For amounts to incorporate, read the product labels. By the way, before amending your soil, it’s a good idea to begin with a soil test. See our related article on that topic.)

Coffee Grounds. Available for free from many coffee shops, including St. Louis Coffee Roasters, Kaldi’s and Starbucks, coffee grounds help break up soil, and can be slightly acidifying. Apply as a side dressing to plants or incorporate into compost. Also a key component to vermicasting (worm farming).

Compost. Composted green waste from leaves, grass clippings, non-animal table waste and other sources provides many benefits to the garden, including nutrients and soil conditioning. See Patrick Geraty’s article in this issue for more about how compost improves all gardens.

Cotton Burr Compost. Consisting of byproducts from cotton fiber harvesting, cotton burrs contain a significant amount of NPK and micronutrients, but have a relatively low carbon/nitrogen ratio, so don’t tie up nitrogen like wood products. It helps loosen tight clay soils and improves moisture retention and drainage.

Earthworm  Castings, Fish Emulsion, Bat Guano, and other “End Products.” Favored by organic gardeners in particular, these are more fertilizer products than soil amendments, but like farm manures, these organic fish, worm and animal wastes help improve soil structure in ways synthetic fertilizers don’t.

Farm Manures. Cow and horse manures, properly composted and aged, provide key nutrients to plants, and also condition clay soils, improving drainage and reducing compaction.  Care should be taken in vegetable gardens, particularly around root crops, to ensure that manure is completely aged and composted.

Mushroom Compost. After mushrooms are harvested,  the spent growing media (composted farm waste that may include chicken manure, straw/hay,  corn cobs, cotton seed hulls and gypsum, plus sphagnum peat moss and limestone) still has plenty to offer garden soil in terms of nutrients and soil conditioning capacity.  Can be used as a mulch or soil amendment.

pH Adjusters. Lime, sulfur, wood ash and other products can be applied to soils to adjust pH up or down, depending upon the results of a soil test. Don’t assume you need to apply lime every year unless a soil test confirms it.

Sand. Many people regard sand as an effective product to break up clay soils. Unless applied at very high rates (incorporating up to 80% of soil volume) the blend of sand and clay is more likely to result in adobe-brick-like soil structure.

Soil Conditioners. Calcined clay, also called Fuller’s earth, is a product that is mined, crushed into granules and heated to extremely high temperatures to form ceramic granules that work to physically break up clay soils (kitty litter isn’t the same, despite internet “experts”—it begins with the same material, but isn’t heated to extreme temperatures,  so it melts (or clumps) when moisture is added). Turfaceâ and Profileâ are a couple brand names. Very effective when applied at significant rates. Gypsum, or calcium sulfate, works chemically, not physically, to break up clay soils. It is more effective when soils have a high sodium salt content,  and is less effective if they don’t. Use it by roadsides and sidewalks where snow salt accumulates, or if a soil test indicates sodic (high sodium) soils.  Liquid Soil Conditioners such as compost tea and commercial products like Earth Right Super Stuff and Monty’s Soil Conditioner, are typically blends of ingredients found naturally in healthy soils and compost, such as humic acid, enzymes, microbes and micronutrients. When applied regularly, they are said to help break up clay soils and improving soil aeration and drainage. Use in conjunction with,  not instead of, applications and incorporation of rich, organic matter.

Topsoil. Use it only to change grade, create berms, fill in low spots in the lawn or to blend with other organic and inorganic soil amendments. Topsoil by itself adds little benefit to clay soil.

Robert Weaver is the editor/owner of The Gateway Gardener magazine. He is also an Advanced Level Master Gardener and holds an Associate’s Degree in Horticulture from St. Louis Community Colleges-Meramec. He has been a garden writer for more than 10 years.