FEBRUARY 17, 1997
Gardening: Soil preparation in the vegetable garden
by Holly S. Kennell, Extension Agent, Washington State University Cooperative Extension
Last week, this column gave you a lot of good advice about fertilizing. Vegetable gardens were mentioned as needing regular fertilization. This week I would like to elaborate on that, assuming that some of you may be thinking about digging up a plot for a food garden. (In truth, these same recommendations could be used for a flower bed of annuals or any area that is going to be gardened very intensively.)
About this time of year, we are eager to be outside working the soil. Unfortunately, this has been a very wet winter, so the soil in many yards is still too soggy. With sandy soils you can start whenever you like, but test clay or silty soil to see if it is dry enough. Squeeze a handful of soil into a ball in your palm. If the lump falls apart easily when you tap it, it's ready. If it dents, but holds together when tapped, let it dry out some more. Working set soil hurts its structure and makes clods that dry like bricks.
As you work your soil, you will add organic matter and fertilizer, as well as lime, if needed. Compost, manure, peat moss, grass clippings, and aged sawdust are the kinds of organic matter that will benefit your soil. As mentioned last week, they are not fertilizers, but might be called soil conditioners. Add as much as you can now and dig more in every time you replant. If you have a very sandy, poor soil or a sticky, claylike one, organic matter is your best friend. It will improve the worst soil and make a loamy soil a joy to work.
Fertilizer and lime should be added in amounts recommended by a soil test. Information about how to take a soil sample and about various labs that do nutrient testing, is available from your county Cooperative Extension office. A soil test will tell you what nutrients are present in your soil. Choose a soils lab that interprets the results and you learn what nutrients your soil needs in what quantity. Then you can accurately add exactly what your crop requires. (Shop around for a soil test lab. Their services and prices vary considerably.)
If you don't have time to have a test done, try 2 pounds (4 cups) of 5-10-10 per 100 square feet or 100 feet of row. Many people like to stay strictly organic in their food garden. The nutrients in most organic fertilizers are not as concentrated, so you must compensate by using more. I usually mix up my own organic fertilizer, using this "recipe:" 4 cups of blood meal (or 7 cups cottonseed meal), 4 cups of bone meal, and 4 cups of kelp meal (or 8 cups wood ash). This mix is enough fertilizer for 100 square feet or about 4-foot by 6-foot beds.
The three numbers (for example, 5-10-10 or 6-4-3) on any fertilizer package give the percentages of nitrogen, phosphate and potash. Make sure your fertilizer has some of all of these elements. The second two elements are important for flower and fruit production, but nitrogen is the main fertilizer needed for leafy growth. If you are growing lettuce, spinach, mustard greens, kale, collards, etc., you probably won't need much of anything but nitrogen.
Don't forget to add lime. It's best to apply lime when the soil is as dry as possible, allowing it to be mixed in well. Ideally, we lime the soil in the fall. Then it has time to adjust the soil pH by spring planting time. Most veggies (potatoes are the exception) would prefer a pH between 6.5 and 7.0. Because of our leaching rains, our soils in Western Washington are naturally acidic, so additions of lime are essential. A soil test will give you specific recommendations. General guidelines are: for every 100 square feet of sandy soil--4 pounds, loam--6 pounds, claylike soil--8 pounds. Reapply lime every 2 years (three years for clay soil).
Air also needs to be added to the soil and is the thing most often forgotten. For roots to grow well, the soil must be loosened deeply. If the roots can go down instead of sideways, you can space your plants a lot closer. That means more carrots per square foot (or more petunias).
Visit WSU's Agriculture Site on the World-Wide Web at http://www.cahe.wsu.edu.