Q: I’ve heard about soil tests. What are they and should I have one done?
A: Soil is like an all-you-can-eat buffet for plants. Soil provides food to plants and different kinds of plants need different kinds of nutrients. A soil test can help you decide what fertilizers and organic amendments you should add to your soil when starting lawns, flower beds, or vegetable gardens.
If the plants in your home landscape are struggling, the problems are not always soil related. A standard soil test will not identify the most common garden problems such as over-watering, under-watering, poor soil drainage, soil compaction, diseases, insects, weed competition, too much sun or shade, poor plant varieties, or just neglect.
Most often, a soil test is a good place to start before beginning new plantings. Soil can also be tested at any time although spring and fall sampling are usually the most convenient.
There are many varieties of soil tests although most home gardeners start with a basic test which costs about $20.00. The report can be quite complex but each report interprets the various numbers and offers soil management suggestions. Master Gardeners at the Colorado State Extension office can also help you interpret your soil test.
Colorado State University performs soil tests that provide gardeners with a variety of soil nutrient information. Soil can be tested to measure soil pH which is the acidity or alkalinity of the soil, organic matter, salts, nitrogen, and micronutrients like phosphorus, potassium, zinc, iron, copper, manganese, and lime.
For example, lawns need a different mix of fertilizer nutrients and organic matter than native perennials or vegetable gardens. Soil test information allows you to amend your soil with fertilizer and organic matter so that whatever you plant in a given area will thrive.
The type of sample you send to the lab is very important. The results are only as good as the sample and you will need a soil test for each area of your yard depending on what you want to plant.
Samples are most easily collected using a soil tube or soil auger. A garden trowel, spade, bulb planter, or large knife also works. Each sample should be a mix of soil collected from randomly selected spots within the planting area. Do not include any sod, or plant matter. Collect the soil in a clean plastic pail and mix thoroughly. Place about one pint of the soil mix into a sample bag or box. Label the sample container (for example front lawn, vegetable garden, and flowerbed) and keep a record of the area represented by each sample taken. Send the samples to the soil-testing lab.
How deep you dig is critical and varies by the type of test and for various labs. Follow sampling depth directions given by the lab. For example:
Garden (vegetable and flower) 6 inches
Lawns, new (prior to planting) 6 inches
Lawns, established 3 inches
For more detailed information on the variety of available soils tests, the information each variety provides, and the costs of each test, go the Colorado State University horticulture link at: www.ext.colostate.edu/pubs/garden/pubgard.html or www.extsoilcrop.colostate.edu/Soil Or you can request basic information on soil testing from the CSU local extension office.
Contributed by Deb Ross, Colorado Master Gardener. For answers to your horticultural questions, contact the Master Gardener Help Desk at 636.8921 or CSUmg2@elpasoco.com (A version of this article appeared in The Gazette on 3/7/09.)