As the gardening season gears up, one of the common questions we get as A&M AgriLife Extension agents is about fertilizing our plants. Vegetables, fruit trees, flowers and lawns all need an adequate amount of nutrients to grow and deliver peak performance. You can have a plant with the best genetics, but if it is “starving”, it will not grow as expected.
While we might be able provide generalities about a particular plant’s nutrient needs, we are not going to have a clue about your particular soil’s nutrient status. For example, a sandy soil will not have the same needs as a soil with a high percentage of clay. Also, if you have made fertilizer applications recently, there could still be a residual of certain elements, meaning you may need to alter the analysis to avoid over-fertilizing, which is not only wasteful, but also can pollute the environment. You might not even need to fertilize at all.
Another major factor affecting a plant’s ability to utilize the nutrients in the soil is the pH of the soil. pH is a measure of the soil’s acidity. If the pH is not in an ideal range, nutrients in the soil, or added in a fertilizer, cannot be adequately taken up by plants. Strongly acidic soils, common in East Texas, also release elements like aluminum that are toxic to plants in high levels.
Strongly acidic soils are corrected by the addition of lime. But how much to apply depends on the pH level, the type of soil you have, and the type of plants growing in that soil. Clay soils require more lime than sandy soils to adjust the pH level, and the amount to apply per 1000 square feet could range from 0 to 50 pounds or more, again depending on the pH. Soil testing is the only way to know for sure. Adding too much lime, or adding when it is not needed, can also cause other problems.
As I mentioned, you may have a strongly acidic soil, but if you are growing blueberries, azaleas or centipede grass, the pH may be just right, and the addition of lime would be counterproductive or even harmful to the growth of those plants. Different vegetables have a differing pH preference, with some preferring more alkaline soils, other on the acidic side.
So, how are you going to know what’s really in your soil, and what needs to be added for the lawn, garden or flowers? Get a soil test done. It is an inexpensive and simple process, and easily pays for itself by providing you with accurate recommendations based on your soil and kind of plants that are growing there. The soil testing labs at Texas A&M and Stephen F. Austin State University have state-of-the-art equipment, which are daily calibrated to provide the most accurate results you can get. Kits purchased at stores may give you general ranges, but often are not specific enough.
County Extension offices do not do soil testing, nor mail soil tests to the University labs. But, soil testing submittal forms and collection bags are available at every county A&M AgriLife Extension office. Submittal forms are also available online at the Texas A&M AgriLife Extension Soil Testing Laboratory web site (http://soiltesting.tamu.edu ). On that page, click on “Our Submittal Forms”. For home lawns and gardens, select the Urban Soil test form. You can use a zip locking plastic bag for your soil sample(s). The Soil Testing Lab at A&M in College Station charges just $10 for a regular test, and you should get your results back within a couple of weeks.
The submittal form has simple directions for correctly taking a sample and a form to be filled out. It is important to follow the directions for taking your sample. Take samples from several spots in the lawn or garden and mix them up in a plastic bucket. This reduces the chance of getting an erroneous reading if just one spot is sampled (for example, a dog may have “used” that spot recently). Don’t just scoop soil from the top of the ground. Take vertical slices of soil about 4 or 5 inches deep.
The report will tell you what nutrients are already in your soil and how much you need to apply for your type of lawn grass or garden plants. It also makes a lime recommendation if the pH is too low. It takes all the guesswork out of fertilizing your plants.