Your lawn will gradually thin and weeds may invade. Proper and timely fertilization can be good for both your lawn and the environment. There is less chance for nutrient and soil runoff to surface waters from a healthy stand of grass than bare soil or thin grass. Healthy lawns will have less disease, insect and weed problems, reducing the need for pesticide applications. Well-maintained lawns look appealing and are more wear tolerant.

There are some definite do’s and don’ts when it comes to fertilizing Virginia’s home lawns in the fall, primarily in terms of appropriate timing for the many grasses that are grown in this state. This article discusses fertility programs for cool- and warm-season grasses that will promote the health and quality of your turf, as well as protecting the environment.

Timing is everything. Fall is the OPTIMAL time to aggressively fertilize cool-season turfgrasses (bluegrasses, fescues, and ryegrasses). Cooling (but still warm) temperatures and shorter days are ideal conditions to maximize root growth and food storage in cool-season turfgrasses. The period from September through November is the time of year to deliver the annual nitrogen (N) fertilization requirement, so don’t miss the chance to optimize your turf quality as well as its health.

For warm-season grasses (bermudagrass, zoysiagrass, centipedegrass, and St. Augustinegrass), fall is a time to prepare the turf for winter dormancy. Refrain from additional N applications and ensure your soil test indicates appropriate pH, phosphate (P), and potash (K) levels as you put the turf to bed for its winter nap.

Fertilizer choices. There are lots of things to consider in fertilizer selection. First, what’s in the bag? Left to right, the numbers on the fertilizer bag indicate the % of nitrogen (N), phosphate (P), and potash (K) on a weight basis. Hence, a 50 lb bag of 10-10-10 contains 5 lbs each of N, phosphate, and potash (and even for liquid fertilizers, the analysis still represents % by weight). Next, look at the fertilizer label for some additional information on precisely what other nutrients are contained in the bag, and perhaps most importantly, what type of release characteristics the N has. If the source contains slow release N, you will see a reference to a certain percentage of WIN (water insoluble nitrogen) on the label. Many synthetic turf fertilizers purchased right off the garden center shelves contain between 20-30% WIN. These predominantly water soluble sources can be safely applied at levels up to 1 lb N/1000 sq ft. according to the grass and the season. Most organic manure-based fertilizers can contain up to 75-85% WIN. These materials can be applied at levels up to 1.5 lbs N/1000 sq ft and will provide very sustained growth and color responses with minimal potential for environmental impact. However, most are very low analysis (only 5-8% N by weight) and very large amounts of product are needed if trying to apply normal N-use levels. Used properly, almost any source of N can promote desirable turf responses with little if any environmental impact; it’s the user, not the fertilizer, who creates the problems.

What about other nutrients? Any nutrient that is deficient will limit growth of our turf and landscape plants, so apply them as indicated by soil tests. However, it is very important that we pay attention in particular to phosphorus applications since it is known to be a major contributor to water pollution when mis- and/or over-applied. The days of using a complete fertilizer such as 10-10-10 should be over when we have fertilizers specifically developed for turf use that emphasize N and minimize phosphorus. Standard turf fertilizers will have N labels of 23-30%, 3-5% phosphate, and 5-15% potash.

Think about "non-target" effects of your fertilizer. What I mean here is to consider where your fertilizer ends up after the application. Your turf serves as an excellent filter of chemicals, nutrients, and water, but it is obviously important to apply these resources TO the turf. If your fertilizer ends up on the street, sidewalk, or patio, take an additional few moments to sweep or blow the fertilizer back into the turf canopy. Any granular material sitting on a hardscape is only minutes away from entering our lakes and streams when we have our next rainfall event.

You should determine the amount and frequency of fertilization that is proper. This will be influenced by the quality desired, source of nitrogen, soil type, type of turfgrass, length of growing season, traffic, shade, and whether clippings are recycled. Evaluate your lawn situation based on these factors and how each affects the amount and frequency of nitrogen application. Choose the amount and frequency that best suits your situation.

Soil Type - Sandy soils will generally leach more nitrogen than silt loam and clay loam soils. Therefore, more frequent nitrogen applications are often required in sandy soils when quickly-available sources of nitrogen are used. Leaching can be minimized by using slowly-available nitrogen sources, which in turn can reduce possible contribution to the problem of nitrogen-enriched water in nearby streams and lakes.

Type and Age of Turfgrass - Nitrogen application to cool season grasses such as Kentucky bluegrass, tall fescue, perennial ryegrass, and the fine fescues (creeping red fescue, hard fescue, sheep fescue and chewings fescue) is best done in the late summer and fall period. Warm-season grasses perform best when nitrogen is applied in the mid-spring to mid-summer period. Newly established lawns or lawns lacking density or ground cover will benefit from properly timed applications of nitrogen until ground cover and density have reached a desirable level. Mature zoysiagrass, centipedegrass, and fine fescue lawns require lower levels of nitrogen than Kentucky bluegrass, tall fescue, perennial ryegrass, or bermudagrass.

Shade - Grasses growing in heavily shaded areas require only 1/2 to 2/3 as much nitrogen as grasses growing in full sun. Shade also affects the timing of nitrogen applications. Since grass plants in shade can best use nitrogen when sunlight can reach the grass leaves, fertilizer applications should be timed after the majority of leaves have fallen from the trees in the fall. Applications made in October and November are generally most effective. In heavily shaded areas with fine fescue turf, it may be beneficial to reduce fertilization rates even further or omit applications until leaf collection is finished in the fall.

Quality Desired - Turfgrass quality is a measure of density, color, uniformity (free of weeds and off-type grasses), smoothness, growth habit, and texture. If high levels of turfgrass quality are desired, a commitment must be made to proper turfgrass species and variety selection, frequent mowing, and to slightly higher rates of nitrogen and increased application frequency. Additionally, irrigation, aeration and pesticide application may at times enhance quality.

Clipping Recycling - Significant amounts of nitrogen and potassium are returned to a lawn when clippings are returned. Recycling turfgrass clippings contributes very little to thatch, provides nutrients and organic matter and an environmentally friendly method of clipping disposal. If clippings must be collected, higher rates of nitrogen and potassium applications may be necessary. So use a "mulching" mower and save money!

Micronutrients - Fertilizers that contain micronutrients are most suited for application on sandy soils.

Fertilizer application equipment and methods - Nitrogen fertilizer will "green-up" a lawn. Therefore, it is important to uniformly apply nitrogen-containing fertilizers. This will eliminate streaking caused by different shades of green turf in the lawn. Proper application of nitrogen fertilizers by hand is difficult, even for a trained professional. Drop-type or rotary spreaders should be used. When using drop-type spreaders, be sure to overlap the wheel tracks, since all the fertilizer is distributed between the wheels. Drop-type spreaders are not as easy to maneuver around trees and shrubs as rotary spreaders. Rotary spreaders usually give better distribution where sharp turns are encountered because they tend to cover a broader swath and fan the fertilizer out at the edges of the swath. It is advisable to apply one half of the material in one direction and the other half in a perpendicular direction until one is experienced with a spreader. This will minimize streaking. Avoid application of any fertilizer to non-turfed areas (driveways, roads or bare soil) since it is then prone to runoff into drainage ways at which time it can enter water supplies.