Fertilizing Your Lawn & Landscape This Fall

Article for the Week of October 21, 2006

We are quickly approaching San Antonio’s first traditional frost date of mid-November. There are a couple of important tasks to do NOW to insure the health of your lawn and landscape this winter. The most crucial is the fall application of fertilizer; this is commonly referred to as “Winterizing.” Many folks are wondering when to apply fall fertilizer, what analysis to use, and how much to apply. The important thing to remember is that the fall application of “Winterizing” fertilizer is the most critical. If you were given the option of applying fertilizer only once a year to your lawn or landscape, the best choice would be a fall application.

Fall fertilization is applied when shoot growth slows or around the time of the season’s last regular mowing. Because of favorable environmental conditions (cool temperatures, short days, and high light intensity) nitrogen applied at this time aids the photosynthetic production of carbohydrates. These carbohydrates are stored for use the following growing season, providing an earlier spring green-up and an energy source for turf grasses to recuperate from drought and other related stresses.

Another reason for fall fertilization is to reduce the need for high amounts of spring-applied nitrogen. Too much spring fertilization can actually reduce carbohydrate reserves and root development by inciting rapid shoot growth. This is because growing shoots take priority over roots for carbohydrate use.

Both spring and summer fertilization is used to maintain the color and density produced by fall fertilization the previous year. Fertilization at these times should not produce succulent plant tissue which can increase the severity of turf grass disease and reduce the plant’s ability to withstand heat, drought, mowing or wear stress.

Warm season’s grasses such as, Bermuda, Zoysia, and St. Augustine, most root growth occurs in spring and summer. Fertilization during these warm seasons stimulates root growth. The roots of Bermuda and St. Augustine grasses the lawns die in the spring following green-up. Heavy fertilization in early spring may result in more stress during this critical survival period.

What is the best kind of fertilizer to use in the fall? For many years, high phosphorus fertilizers (high middle number) were popular for fall use but through research we now know that these can actually reduce winter hardiness and impede spring recovery. Furthermore, in this area of Texas, excessive applications of phosphorus will tie up the iron and zinc in our soil and result in yellow, weakened grass.

The application of a complete fertilizer which is high in nitrogen and potassium will enhance fall lawn color (prolongs color retention) and promote early green-up next spring, plus give added cold hardiness. The actual phosphorus level should be lower than that of the nitrogen and potassium. The best nutrient ratios for fall fertilizer are 3-1-2 and 4-1-2. In the nursery you will find these ratios in such fertilizer analysis as an 18-6-12 or a 19-5-9.
The fall application of fertilizer should take place in mid-to-late October. NOW! The amount needed is in terms of actual nitrogen to be applied is NO more than 2 pounds of actual nitrogen per 1000 square feet. This equates to about 40 pounds of 18-6-12 on a 7200 square foot lawn. The average size of a front lawn is approximately 5000 square feet, so the remainder can be used on established plants in the landscape.

The slow release nitrogen fertilizers are beneficial in the fall since a quick uptake by the plants is important. In the fall we want the nitrogen to be available to the grass quickly so that it can be taken up into the plant and utilized. Besides, slow-release fertilizers are much more expensive because of their slow-release mechanisms.

Consider applying at this time, Texas greensand at a rate of 10 pounds per 1000 square feet. Since soils are very basic and alkaline, the Texas greensand will help loosens the heavy clay soils and provide essential micro-nutrients such as iron. Feathering a ½ inch to ¾ inch top-dressing compost to the lawn will also provide enriched nutrients as well as a deeper more defined root system.

The second task is a must to insure a healthy turf controls brown patch. Brown patch is a fungus disease that attacks St. Augustine grass in cool, damp, fall weather, and will weaken the lawn going into the winter. It is identified as a circular area in the lawn, usually 3×10 feet in diameter. In the edge of the area you will see brown or yellow grass, yet the interior of the circle may be a healthier green. Pull blades of grass at the edge of the circle, if the blades pull easily away from the stems and look brown and rotted at the base of the blades, then your lawn has brown patch and should be treated. The most economical and effective fungicides that control brown patch is Terraclor (PCNB) or Ferti-lome F-Stop.

To help prevent brown patch from getting started in the lawn, do not water in the evening. Water droplets that stay on the grass all night will spread the brown patch spores. Therefore, water in the early morning hours so that the grass will dry out during the day and before nightfall. Do not walk on or mow your contaminated lawn, so that further spreading will not occur.

One other important chore in the lawn and entire landscape to prevent winter damage is watering thoroughly during the winter. Although the top of plants may go dormant during the winter, the root system does not, and the grass needs moisture to continue growth. Also, its fact that a well watered plant is less likely to suffer freeze damage then a drought stressed plant. So get out there this winter and water that landscape at least once a month in lieu of rainfall.

Fall fertilization controls brown patch and with watering it will insure that our lawns will be well on their way to a healthy next season.

Tree and shrub health is also important and fertilization at the proper times insures tree and shrub overall health. I also recommend that you take the time this fall to fertilize your trees and shrubs using the same “Winterizer” fertilizer which is recommended for grasses. During the fall period of maximum rainfall, plants absorb nutrients more effectively. Summer and winter are not optimum times to fertilize. Hot temperatures cause the soil to become dry and compacted; in cold weather, plants are dormant, and the soil is not workable.

In the forest, trees draw nutrition from a steady supply of organic plant and animal matter such as decomposed leaves. This layer of matter covering the forest floor acts as a fertilizer. Like mulch, it helps the ground hold moisture and maintains moderate temperatures.

But in tidy backyards and other landscaped areas, this nutrient-rich layering process doesn’t often take place. Instead, the ground is covered with lawn, which must compete with trees and other plants for nutrients and water. Construction and other land-use projects may alter the soil by adding pollutants and rubble to it.

Without the balanced natural environment, even vigorous, specimens may have some trouble. Because a plant’s well-being depends on its ability to grow, the health of the root system is crucial. Roots must keep drawing sufficient nutrients and water to sustain growth. But as they continue to grow, at some point, they’ll run into restrictions such as pavements, structures, rocks, rubble, roots of other plants, and hard compacted soil. With such conditions, they may not be able to absorb nutrients and water as easily as before. These restrictions result in less new growth, pale color, and damage due to insect attacks and disease. To overcome these growth inhibitors, trees and shrubs need good care and maintenance.

Timing, knowing when to fertilize is vital to top quality plant care. It’s important to fertilize plants at or during a certain time so the tissues of the new growth will toughen sufficiently to weather the first freeze. Without this “hardening-off” and easing into dormancy, the plant can be severely damaged by winter stress. Proper timing will help you promote dormancy early enough to prevent such damage.

Fertilization keeps trees and shrubs from falling victim to health problems such as decaying. Resilient limbs and general vigor make them sturdy enough to weather storms and extreme temperatures. And the healthier they are, the more beautiful they look.

Remember, Learn and Have Fun!

David Rodriguez is the County Extension Agent-Horticulture for Bexar County. He represents Texas Cooperative Extension with the Texas A&M University System. For any landscape or gardening information, call the Bexar County Master Gardeners Hotline at (210) 467-6575, e-mail questions to mg-bexar@tamu.edu, or visit our County Extension website at https://bexar-tx.tamu.edu/.

Special Note: Listen to live broadcast of the Home & Garden Show with David Rodriguez & Bill Rohde on WOAI 1200 AM, every Saturday morning between 8:00-11:00 a.m., and call in your gardening questions at (210) 737-1200 or 1-800-383-9624. Check it out!

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