David M. Kopec, Extension Turfgrass Specialist
This issue will address the maintenance of dormant bermuda, overseeded bermuda and fall fertilization for cool season grasses at high elevation locations in Arizona.
Many homeowners will prefer to let their bermudagrass turf go dormant during the fall of the year. There's nothing wrong with this and in fact, it's better for the lawn in most cases.
For people who want to extend the length of the growing season of the bermuda, multiple applications of iron at 2-4 ounces of actual iron per 1000 ft2 should be made. The first application should be made on October 1 and then again 10 days later, and finally 10 days later again. Don't try to apply nitrogen fertilizer to the bermuda. It may actually hurt the grass by interfering with winter food storage. This can be a cause of poor green up in the spring. There is some new discussion about late season nitrogen fertilizer on bermuda.
Dormant bermudagrass will turn browner quicker in areas away from trees and in areas which are drier than others. This is normal. After it goes dormant, bermuda needs about 1/2" of water per month to keep the stolons from drying out. This usually occurs from winter rains. An alternative to overseeding bermudagrass lawns is to spray green turf paint over the bermuda after it turns brown in the fall.
For overseeded lawns, the biggest mistakes that are done include improper mowing frequency and improper mowing heights. Annual ryegrass should be mowed to 2.5 inches when it reaches 3.0 inches. It does not like to be shorter than 2.0 inches. If the "short look" of 2.0 inches is desirable, than mow it to 2.0 inches when the grass is 2.5 to 2.75 inches, at most! Many people try to make annual darker in color by applying nitrogen in sometimes excess amounts. This can cause fertilizer loading in the soil. The ammonium (NH4) form will stay in the soil till the spring. At that time, the soil bacteria convert the NH4 to more usable nitrate (NO3). For fall fertilization of either annual or perennial ryegrass, apply small amounts of nitrate forms (ammonium nitrate or potassium nitrate) at 1/4 lb. of actual nitrogen per 1000 ft2. Do this four weeks after the first mowing and again every 21 days afterwards. Application of iron at 2-4 ounces per 1000 ft2 once a month will keep things green, especially when the soil is cold and wet.
For high elevation areas 5500 and above, or where cool season grasses are used year round, fall is the best time to dethatch Kentucky bluegrass turf and follow with fall fertilizations.
September is the best time to dethatch KBG turf in Payson, Winslow,
Flagstaff. Dethatch in at least two direction. Rake up excess thatch, or catch it in the mower basket, or mulch it in place with a mulching mower.
Follow immediately with an application of fertilizers. Use either a complete fertilizer with a 3-1-2 ratio, or apply superphosphate (1 lb. -P-/1000 ft2) and potassium nitrate (1.5 lb. -N-/1000 ft2).
If you use a complete fertilizer (N-P-K), apply it at the 1.5 -N-/1000 ft2 rate.
Apply a second application of ammonium phosphate by November 7. The
ammonium will stay in the soil and the phosphate will be used for winter
root growth. KBG makes most of it's new root initials in fall and winter.
This "late fall" fertilization helps KBG tremendously.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona. The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.