Should grasses be fertilized in the fall? The answer depends on what type of grass is being grown.
Our turf grasses are either warm-season grasses or cool-season grasses. The different types are fertilized at different times of the year.
The cool-season grasses, -- fescue, Kentucky bluegrass, etc. -- are fertilized in the fall. Fall is when this type of grass gets the majority of its fertilizer. Cool-season grasses need no fertilizer in the summer because they are slowing their growth to survive our summers.
Most of the turf grown in our area is warm-season grass. Warm-season turf grass is fertilized in spring and summer.
As fall and winter near and the days get shorter, the warm-season grasses slow down and start to harden off for winter. They are not using or taking up the nutrients as they were in the spring and summer, so most fertilizer applied in the fall is not taken up by the grass. Also, nitrogen fertilizer causes the grass to continue to grow. This keeps the plants tender and more susceptible to cold damage.
One nutrient that can benefit the grass in the fall is potassium, which is the last number on the fertilizer bag. Potassium strengthens cells and cell walls. It increases winter hardiness and drought and disease resistance.
There are fertilizers that only have potassium in them. One of these is muriate of potash. A soil sample is the best way to determine the level of potassium, which will determine if more potassium needs to be applied in the fall. If the soil sample shows a high level, extra potassium is not needed.
The major problem with fall fertilization of turf grass is diseases. Two diseases -- large patch and take-all disease -- become major problems in the fall. Both like wet conditions, cool temperatures and an increase in nitrogen. They will attack both cool-season and warm-season grasses.
Large patch is caused by the fungus Rhizoctonia. Several species of this fungus attack turfgrass. In cool-season grasses, it is called brown patch. In warm-season grass it is known as large patch.
This disease starts as a small circle and continues to spread out from the starting point. A yard could have several of these circles, and they can grow together to cover a whole yard.
To help identify large patch, look at the border where the healthy grass meets the diseased grass. Early in the morning, while the grass is wet, a smoky, gray color on the grass can be seen. As the grass dries, this color will go away.
This is the reproductive part of the fungus.
To treat for large patch, apply a fungicide and change the way the grass is managed. Any fungicide for lawns works on large patch. Let the grass dry out by watering less often but deeper. Don't apply any nitrogen fertilizer to the grass.
Take-all disease started showing up in our area a number of years ago. This disease attacks the grass about the time we get our first frost, so the symptoms don't show up until the grass fails to green up in the spring.
This disease likes late applications of nitrogen and wet conditions. The disease is caused by the fungus Gaeumannomyces graminis . Take-all likes soils with a high pH level -- above 6.5. Therefore, don't apply lime unless it is called for by a soil sample.
To control this disease, the soil drainage has to be improved. Use ammonium-based fertilizers during the growing season; apply manganese sulfate at 2 pounds per 1,000 square feet; and apply a fungicide during the first week of October and again the third week of October. Bayleton or triadimefon can be used to help control this disease.
The timing of the application is important. Also, high potassium levels will help with this disease.
With warm-season turfgrass, fertilizing at the right times can help reduce a number of problems in our lawns.
Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at email@example.com.
The Columbia County News-Times ©2013. All Rights Reserved.