Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
10/18/99
Yard and Garden Column for the Week Beginning Oct. 22
Contacts:
Carmen Sanogo, Extension Plant Pathology, (515) 294-0581,
csanogo@iastate.edu
Elaine Edwards, Extension Communication Systems, (515)
294-5168, eedwards@iastate.edu
Preparing Your Lawn for the Winter
By Carmen Sanogo
Research associate
ISU Plant Disease Clinic
The summer season is over and Iowans are gearing up for the cold winter months. Some of you were so successful in gardening that you now have shelves full of canned fruits and vegetables.
So why worry about the lawn now? Think back to last summer. Remember those brown circles of dead grass in your lawn that never seemed to go away? What about your frustration when you discovered that your green grass had developed unsightly brown patches when you returned from vacation? Where did all those ugly spots come from? How did they get there? The bare spots haven't disappeared, and may pop up in other places next spring unless you do something about them now.
If your lawn had diseases such as summer patch, brown patch or necrotic ring spot, fall is the time to catch up. Filling in the empty spots this fall, by reseeding or laying new sod, may cover up the damage but will not entirely solve the problem. To help your lawn fight future disease outbreaks, proper mowing, fertilization, watering, aeration and dethatching can be very helpful.
Do not underestimate the importance of taking good care of your lawn in the fall. Cultural practices such as proper fertilization can help prevent damage from diseases. For example, applying nitrogen during the fall can speed the recovery of lawns damaged by diseases such as leaf spot. Fertilizing during fall is important because it helps build vigorous root systems. And strong roots translate to a healthy grass plant - one which can withstand attack by the fungi that cause summer patch and necrotic ring spot.
Most of the total annual nitrogen for cool-season grasses should be applied in the fall months. The dormant application, which usually goes down after the last mowing, is especially important. This is the time when shoot growth shuts off and food is diverted to the production of roots, rhizomes and stolons. If you are not sure how much fertilizer to apply, it is always worthwhile to have a soil analysis done.
Use a complete fertilizer -- one that contains nitrogen, phosphorus and potassium (N-P-K). For example, a fertilizer product labeled "15-5-10" means that it contains 15 percent nitrogen, 5 percent phosphorus and 10 percent potassium. The remaining 70 percent is inert materials that help in the even distribution of nutrients in the soil.
Nitrogen is needed in larger amounts than phosphorus and potassium because it is responsible for shoot and root growth and protects the grass plants from damaging diseases, heat, drought and cold stress. Both P and K help in the production of an extensive root system and increase the plant's ability to ward off environmental stresses and diseases. Slow release nitrogen sources such as sulfur-coated urea, methylene urea and isobutylidene urea (IBDU) are often recommended in spring to effectively manage disease by discouraging excessively rapid, lush growth and the thatch build-up that results from excessive growth. In fall, a water-soluble, fast-release nitrogen application such as ammonium sulfate can help speed the recovery of grass injured by diseases such as summer patch and environmental stresses.
But before you provide food for your lawn, plan on cleaning it up first. Otherwise, you will end up increasing the thatch layer and encouraging the growth of weeds next spring. The thatch is the brown spongy layer between the soil surface and the green canopy. It is made up of both dead, decaying grass and live roots and shoots. A 1/2- inch thatch layer is considered normal, but more than that requires mechanical removal. After irrigating, if the lawn feels as if you are walking on a soaking-wet sponge or carpet, you have a pretty good idea that it's time to dethatch.
A key in preventing lawn diseases such as summer patch is to reduce the thatch layer. This is where most fungal resting structures hide and survive for many years. A thatching rake with blades that slice through the turf to bring the thatch layer to the surface is useful for smaller lawns. If you have a larger area and you want to save time, consider using a power rake or a vertical mower that has rotating vertical blades to rapidly cut out the thatch. Set the blades in such a way that the soil is disturbed as little as possible.
Soil aeration in the fall helps break the thatch layer and also increase air and water flow in the soil. The effects of diseases such as anthracnose, summer patch and leaf spot tend to be more damaging on high-traffic, compacted areas. Use a foot press if the area is small; for larger lawns, a power-driven core aerator with hollow spikes pulls out plugs so that the water, fertilizer and air can easily enter the soil and roots. But what about the soil plugs? It is best if you leave them on the soil surface to dry. The next time you mow, they will crumble and act as a beneficial layer of soil that will allow for natural decomposition in the thatch layer.
As we move towards the colder months, do we have to worry about the layer of snow on the lawn that we get in wintertime? The answer is no. The snow can act as insulation for lawns and should be allowed to remain on the grass if winter temperatures drop below 32 F. It actually helps protect the roots from freezing. Later in the winter, when the snow starts to melt, and the grass is exposed to desiccating cold winds, it may be helpful to water the lawn to keep it from drying out. The water will not only sustain the grass but also insulate it from lower temperatures. Keeping traffic off the lawn when it is still covered with a layer of ice or snow is a good practice. This will prevent wear and tear of vulnerable grass plants as well as soil compaction.
Just like preparing your car for winter by changing the oil and filter, adding the antifreeze, etc., proper lawn maintenance this fall will save a great deal of headache and anxiety next spring.
Some helpful bulletins on lawn fertilization, thatch control and cultural management can be obtained from your local county extension office or from Iowa State University Extension Distribution at 119 Printing and Publications, Ames, IA, 50011; telephone (515) 294-5247.
ml: isugarden
Extension programs are available to all without regard to race, color, national origin, religion, sex, age, or disability.