A VEGETABLE garden can produce no better than the soil permits. If the soil is too acidic, if it lacks the ability to provide necessary nutrients to the plants, if it is too compact for oxygen to move freely to their roots, results will be disappointing.
The best way to find out about your soil is to have it tested. Even if you have been getting good results, it is desirable to have the soil tested. The soil can deteriorate considerably in one growing season.
You can have your soil tested free or for a small charge at your state university. Phone your county extension agent for instructions on how to take the soil samples and where to send them.
The best time to send the samples to the soil testing laboratory is late fall or early winter. It avoids the spring rush and gives the gardener sufficient time to purchase and apply lime, if needed to reduce soil acidity, and the proper kind and amount of fertilizer. Also, you will find out if there is a real need for application of organic material.
Spring is not a good time to take soil samples. Often the soil is wet, which is not good for collecting samples and it is a busy time when one is trying to get seed into the ground.
Tests performed on samples include soil pH, which is a measure of the acidity of the soil, and tests to measure the available phosphorus, potassium, calcium and magnesium. The laboratory also usually provides special tests for organic matter contents of the soil, available zinc, available boron, and available manganese. Along with these tests, a report is provided giving recommendations for lime and fertilizer needs.
A measurement of soil acidity or alkalinity is like a doctor's measurement of a patient's temperature. It reveals that something may be wrong but it does not tell the exact nature of the trouble.
The pH scale goes from 0 to 14. At pH 7, the midpoint of the scale, it is neutral; pH values below 7 indicate acidity, with the acidity increasing as the pH values get smaller. Values above pH 7 denote alkalinity, with the alkalinity increasing as the pH values get larger.
Liming to reduce soil acidity is an extensive and routine practice in most of the eastern half of the United States. Soil acidity develops gradually in humid regions as calcium and magnesium are slowly lost from the soil by leaching and is speeded by crop removals and by use of the soil. Soils in the western Great Plains and in dry regions usually are neutral or slightly alkaline, rather than acid. Liming there is seldom necessary and often is harmful. Lime-induced chlorosis of fruit trees is an example.
Benefits from liming result from more than mere reduction of soil acidity. Two major plant nutrients, calcium and magnesium, are supplied by liming materials. Regulation of soil acidity is a means of controlling some crop diseases. An example is potato scab, which is less severe in acid soils.
Finely ground limestone is the liming material used in many sections. Calcium carbonate is the active agent in limestone for reducing soil acidity.
Artichoke does best with a pH of 6.5 to 7.5; asparagus of 6.0 to 7.0 in the East and up to 8.0 in soils in the West; beets at 6.0 to 7.5 in the east and up to 8.5 in western soils; broccoli, Brussels sprouts and cabbage 6.0 to 7.0 in the East and up to 7.5 in the West; carrots 5.5 to 7.0; celery 5.8 to 7.0; collards 6.0 to 7.5; cucumbers, muskmelons, watermelons, squash, pumpkins 5.5 in the East and up to 7.5 in the West; lettuce 5.8 to 6.6 in the East and up to 7.5 in the West; potatoes 4.5 to 7.0; sweet potato 5.5 to 6.5 and tomatoes 5.5 to 7.0 in the East and up to 7.5 in the West.