Garden Soil Preparation - April 5, 2006
Jeff Schalau, County Director, Associate Agent, Agriculture & Natural Resources
Arizona Cooperative Extension, Yavapai County
Soil preparation is vital to a successful vegetable or annual flower garden. We need to provide sufficient nutrients and soil amendments prior to planting to ensure production and performance during the subsequent growing season. Adequate tillage coupled with the additions of organic matter and nutrients are the basic components of garden soil preparation. When these materials are combined with proper proportions and placement, your flowers and vegetables will flourish.
Organic matter improves overall soil tilth for seedling establishment and root growth. In challenging situations, organic matter will improve water infiltration and drainage of clay soils as well as water and nutrient holding capacity of sandy soils. Soil organic matter breaks down into humus with the help of native soil microbes, worms, and insects. The soil microbes, worms, insects and plant materials also become soil organic matter. Humus is rapidly leached away in our alkaline soils, so the organic matter pool must be replenished each year.
Good sources of organic matter are garden compost, composted manures, green manures (crops specifically grown to be tilled in), and other “non-woody” material. Peat moss is also a source of organic matter, but it is mined from bogs and not truly a sustainable resource. Straw, sawdust, and other “brown” materials are low in nitrogen and should be composted with other “green” wastes or with nitrogen fertilizer before being added to the garden. Alfalfa meal, feather meal, and cottonseed meal are organic matter sources that also provide nitrogen.
Whatever your organic matter source, it can be spread 2-4 inched thick on the soil surface and tilled in to a depth of 10-12 inches. Fertilizer can also be added prior to tilling. Use a product that is high in phosphorus (the middle number on the label). Phosphorus must be placed where the roots will grow into it. Nitrogen is also a necessary nutrient, but you must consider what the nitrogen content of the organic matter source used as well as the crop being grown. If you are in a limestone area, an addition of soil sulfur will improve soil pH and availability of iron, phosphorus and other nutrients. I use a shovel to till, but a rototiller can make the job easier.
An alternative to spreading organic matter and fertilizers over the entire garden is to prepare soil in beds or rows only. This conserves your organic matter supply by strategically placing it where the plant roots will be. When I plant a row or a bed, I remove the first shovel depth of soil and place it to the side. I place 3 inches of compost, a layer of rabbit manure (for nitrogen), and triple super phosphate (0-45-0) in the hole, then till it in. After this, I rake the soil placed on the side back into the hole and mix again. I don’t use sulfur because my soil is only slightly alkaline (pH 7.5).
Once the amending and tilling are done, the entire area should be raked until it is somewhat level. Irrigate to settle the soil and allow it to dry for a day or so. Never work the soil when it is soaking wet as this will cause compaction and/or ruin soil structure. Rake again and plant seeds or young bedding plants. If bedding plants are used, consider “butterflying” the root system at planting time. This is done by splitting the root system partially in half from the bottom and spreading the split portion before planting. Nitrogen can also be side dressed and watered in during the growing season for nitrogen demanding crops such as corn.
There are many variations on this theme and other methods are outlined in various vegetable and flower gardening books. In arid regions, annual flowers and vegetable crops always perform best when organic matter is added to the native soil. Nitrogen and phosphorus are also needed to grow vigorous, productive plants. After some experience, gardeners generally adapt these basic recommendations into methods that work for them. For more on vegetable gardening, consult the Arizona Master Gardener Manual on-line at: ag.arizona.edu/pubs/garden/mg/.
The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at firstname.lastname@example.org and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: cals.arizona.edu/yavapai/anr/hort/byg/.
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Last Updated: March 30, 2006
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