How Can I Improve My (Expletive Deleted) Clay Soil?

From the garden e-mail bag, Gordon of Lodi writes: "I've about had it with clay/hard pan soil. The soil map for Lodi/Stockton says we are supposed to have sandy loam.  Give me a break!  I bought a 30 lb. bag of gypsum pellets and I'm willing to dig it in everywhere. But, how much do I use? I found an article online. It says to add 20-30 lbs. per 1000 sq. ft. of garden area. I'm not going to work up 1000 sq. ft.!  How about a cup full in 10-20 sq. ft. every three years?"

Gordon, how about getting a soil test done first? California's Central Valley is made up of many different soil types, so yours may not be representative of what you researched. 

Gypsum is effective on soils high in salts; it does nothing to improve the permeability of our clay soils, most of which do not have a salt issue. Still, only a soil test can determine that. By the way, gypsum is very slow to work. It needs to be added (for that salinity problem) on a regular annual basis, not once every three years.

Usually, the reasons for the expletives used against clay soil include symptoms such as slow draining soil, difficult to dig soil, or hardpan layers.

This time of year, especially after a rainy winter, compaction of clay soil is not uncommon (quit walking on wet clay soil!).
  

Don't want to be a scientist? Then, build a raised bed and plant in that, using a high quality commercial soil mix. To improve water penetration, be sure to mix in some of the new soil into the existing soil base at the bottom of the raised bed.

Raised Beds, Fair Oaks Horticulture Center

If you want to improve the soil drainage and permeability of your existing clay soil, add quality compost, top the soil with several inches of mulch, and grow a cover crop. 

The Yolo County Master Gardeners put together an easy-to-understand chart of soil symptoms and possible solutions. More info is available in their online publication, "Using Soil Amendments in Yolo County Gardens."

A word of warning about one of those suggestions: adding sand, perlite or vermiculite to your soil may be counterproductive. According to retired college horticulture professor Debbie Flower, "I would not add those to my field soil: Too little sand added to clay = cement. Perlite is ugly (and it tends to rise to the surface). Vermiculite just compresses when soil is worked or walked on."

Elsewhere in that publication, they explode some of the myths about certain soil amendments: 

Myth #1. Gypsum softens clay or loosens compacted soil. 
Gypsum (calcium sulfate dihydrate) is effective in counteracting the effects of sodium, which in excess (in soil or in irrigation water) causes soil aggregates to disperse, sealing the soil surface and reducing water infiltration. The calcium in the gypsum replaces the sodium, making for more stable soil aggregates, which do not disperse and form a seal so readily. This process is the basis for the misleading claim that gypsum “loosens” the soil. Gypsum does not reduce or prevent soil compaction, dissolve hardpan, soften clay soils, or convert clay to loam. 

Myth #2. Gypsum lowers the pH of alkaline soils. 
In very high pH soils (pH > 8.5, characteristic of high- sodium soils), gypsum will lower the pH, but only slightly. At lower, though still alkaline, soil pH values, gypsum has little or no effect on pH. Chemically, calcium sulfate is a “neutral salt”, i.e., when it dissolves in water, it does not change the pH of the solution. If the objective is to lower soil pH, elemental sulfur, iron sulfate, or aluminum sulfate should be used.

Myth #3. Inoculating soil with microbes or microbial preparations, will improve “dead” or infertile soil. 
A wide variety of “microbial” products that contain (or claim to contain) microorganisms are commercially available for farm and garden use. A review of the claims made for such products is beyond the scope of this bulletin. Keep in mind that most soils, including soils that have been fertilized only with synthetic fertilizers, or have suffered years of abuse (compaction, erosion, loss of organic matter) still contain a great diversity of microbial species. To establish or re-establish a healthy soil food web, all that is needed is to apply a variety of organic amendments and ensure that pH and nutrient levels are adequate for plant growth.

More information about: 
The benefits of adding compost to the soil.
The benefits of topping garden soil with mulch.
The benefits of cover cropping.

 

Crop Rotation and the Circular Garden

I have little or no artistic sense whatsoever, especially in the garden. I tend to plant in rows, in rectangular raised beds, all designed for function, not form. With raised boxes, it's easier to rotate the vegetables each year. 



IF you can remember what was planted where, the year before. 

The benefits to crop rotatation? Many of the plants that are in the same "family group" have diseases in common. Many of these diseases are difficult, or impossible, to control using chemicals. For example, don't plant tomatoes in the spot where you had potatoes last year, and vice versa. That could spread late blight disease. The best solution for disease control is crop rotation. 

Of course, choosing resistant varieties of vegetables can help thwart diseases. For example, tomatoes with a "V" "F" and/or "N" after their names indicates resistance to verticillium wilt, fusarium wilt and nematodes. However, most heirloom varieties of vegetables offer little or no disease resistance...another good argument for crop rotation. For heirlooms, choose those varieties that are meant to grow in the area you live. And, it helps to spread an inch or two of compost over all your garden beds before you plant each year.

Another reason for crop rotation: to replenish nutrients to the soil. Vegetables tend to be heavy nitrogen users. Giving your soil an "off-year" every few years by planting cover crops allows it a chance to reduce pest populations while building up valuable soil nutrients, as well as beneficial fungi and bacteria. 

Not a Cover Crop

Annual cover crops that do well here in California for the warm weather seasons: buckwheat, cowpeas, soybeans and black eye peas. 

Vetch. Not kvetch.

For the cool weather seasons: bell or fava beans, winter peas, vetch, clover. All of these can add more nitrogen to the soil.








An excellent online reference for cover crops: the Peaceful Valley Farm Supply Catalog. That publication also points out several other benefits to crop rotation:
• Increases organic matter

• Increases earthworms and beneficial microorganisms

• Stabilizes soil to prevent erosion

• Brings deep-rooted minerals to the surface

• Provides habitat, nectar, and pollen for beneficial insects while choking out weeds

• Improves water, root and air penetration of soil

• Increases the soil’s moisture-holding capacity

• Breaks up subsoil and plow-soles

• Provides aesthetic value and color (artistic!)

Which brings us back to my original quandary...how to remember exactly what was planted where, each year. Garden gnomes (cleverly disguised as possums) steal the signs; leaving crop remnants in each bed could add to pest and disease problems; writing down the location of crops each year would work...if you remember to go back in the house to check your garden notebook before starting the task of planting each year (ha!). 

One solution that may work is a circular garden, consisting of six raised beds formed to look like spokes emanating from a hub...a pizza garden, if you will. 
There are definite benefits to having a garden in the shape of a circle: a central water source in the middle of the circle, perhaps a small tool shed in that hub area, and compacted walkways three or four feet wide (big enough for a wheelbarrow) to avoid stepping on the garden soil. And it just might be an easy way to remember to rotate crops each season. 

    

Here's the general idea for the Circular Crop Rotation Garden. The crops are arranged so that every three years, the soil gets a break: either nitrogen-fixing crops such as peas and beans are planted; or, a cover crop and compost are added to replenish the soil. Also, crops that tend not to be heavy nitrogen users are situated right before the "rest year". In this case, root crops and leafy crops precede beds that are in minimal use (cover crops or peas/beans). The heavy nitrogen-using beds are directly opposite each other: tomatoes, peppers, etc. are opposite the corn and cucurbits.