Don't fertilize this fall unless necessary

October 13, 2005
Victoria County Master Gardener Intern

Fertilizing and fall winterizing are just around the corner. You have various forms and kinds of fertilizer to choose from, but first, make sure you need to fertilize at all.

There are more and more fertilizers available than ever before. The one that's right for you depends on your type of lawn and garden, the results you want, time of year, how much money you want to put in it and personal choice.

Ask yourself: Do I really need to fertilize? And what type of fertilizer should I use?

Fertilizer is a substance used to make soil more fertile or more capable of sustaining abundant plant life. According to Dr. Jerry Parsons, Texas Cooperative Extension horticulturist, fertilizer increases plant growth only if it is the plant's limiting factor. Plants grown in poorly drained soils, in excessive shade or in competition with tree and shrub roots do not respond to fertilizer.

Plants, like people, must have nutrients to flourish. They need a balanced diet with all of the necessary nutrients readily available for their use. Plants will grow at optimum rates if nutrition is furnished as needed.

Keep in mind that the major pollutant of groundwater is nitrate, which can come from plant fertilizer applications. That's why using slow-release fertilizers to feed plants makes sense. Fertilizers that gradually feed plants are not only environmentally sensible, but they also enable plants to grow at optimum rates.

A recent soil sample survey conducted by Victoria County Extension through the Master Gardener program indicates what Victoria County Extension Agent Joe Janak has been saying for years now: "Start by collecting a soil sample, have your soil tested and apply only the amount of nutrients needed. Too many people over-apply nutrients to their plants. It's easy to do but hard to undo."

In a recent sampling of about 30 samples collected, 22 percent of the samples were either high, very high or had excess amounts of phosphorus and 74 percent of the samples were either high or very high in potassium. Even one organic gardener in the program had excess levels of nutrients. When nutrient levels are too high it can cause increased thatch in turf grass, increased insects and diseases, and even decreased availability of other nutrients, resulting in poor plant growth. All this can evolve into death of plants and pollution.

According to Janak, "Through Extension and the Victoria County Master Gardener program, we have four years of data now with over 300 soil samples, and the trend is still the same - a high percent of the landscapes are over-fertilized."

As a result, we may need to skip fertilizing some sites for three to five years or only apply nitrogen fertilizers as the tests recommend.

If fertilizers are needed, they are available as solids, granules, powders and liquids. The most common or familiar fertilizers are in the form of crystals or granules. These are scattered on the soil and watered in. The irrigation dissolves them and carries them into the soil. Other fertilizers are liquids or soluble powders that are dissolved in water before application. They can be applied by a water hose attachment, water can, or through an automatic watering system attached to a drip irrigation system.

Fertilizers can be applied as solid chunks that are placed in the soil where the plant root can reach them. They may or may not always be slow-release fertilizers and come in the form of spikes, pellets, briquettes and coarse salts.

Nutrients can also be applied in the form of organic matter. Manure is the ancient source of plant nutrients. Compost, dead leaves, and other forms of organic matter also decay to release plant nutrients. Organic matter improves soil structure and adds nutrients. There is little or no chance of plant burning and it lasts a long time.

The word "organic" means that the nutrients contained in the products are derived solely from the remains or by-product of a living organism. Cottonseed meal, blood meal, bone meal, hoof and horn meal and all manures and composts are examples of organic fertilizers. Most of these products packaged as fertilizers will have the fertilizer ratios stated on the package labels just like synthetic fertilizers.

Some organic materials are sold as soil conditioners and do not have nutrient guarantee even though small amounts of nutrients are present. Because organic fertilizers depend on soil organisms to break them down and release nutrients, most of them are only effective when the soil is moist and soil temperature is warm enough for the soil organisms to be active. In our area the microorganisms are active most, if not all the time.

Soluble synthetic fertilizers are produced by chemical reaction, from organic or inorganic materials. These fertilizers release nutrients into the soil quickly and deliver a fast greenup.

They are readily available because they do not depend on microbes, like organic fertilizers do. This means they can deliver at critical time periods, with known effects. These fertilizers demand more work. Their effects are shorter-lived, so they require more applications. Also, the high salt content of soluble synthetics adds the possibility of fertilizer burn. Always follow recommended rates, apply to a dry lawn and water in thoroughly to avoid burning.

After years of using a 3-1-2 or 4-1-3 ratio fertilizer, many landscapes have an excess of phosphorus and potassium. Besides waiting for a disaster to alert you, such as grass or plant problems, you should first test soil. Stop by the County Extension office, soon to be in its new location at 442 Foster Field Drive about one block east of its old office at the Regional Airport, and pick up a soil sample bag. Sending it off now should get you your recommendation in time for fall fertilization - if you need it.