David M. Kopec, Extension Turfgrass Specialist
Many homeowners get "spring-fever" and often start the landscape and lawn campaign early. Usual spring lawn activities include "getting a head start" on mowing , fertilizing and dethatching of bermuda and Kentucky bluegrass at the higher elevations.
"Mismanagement" of grasses at "spring green up" can cause problems which often indirectly weaken root systems and directly weaken shoot systems. Here's the scoop on activities for low and high elevation turfs.
Low elevation bermuda
Homeowners who have left their bermuda dormant and not overseeded almost always have a case where the bermuda is greening up earlier than their neighbors overseeded yard. This is natural since the overseeded turf will keep the perennial or annual ryegrass until later in the spring. The temptation often occurs to "shorten the mowing height" in order to start the season with a lower mowing height and enhanced green color.
When the bermuda is 75% green, it can be mowed, but at the normal mowing height for variety. Common bermuda and E-Z turf is properly mowed at 1.5 inches and Tifway should be mowed at 3/4" or less with a reel type mower. With a rotary mower, common bermuda and E-Z turf can be mowed at 2.0 inches.
Mowing the common or E-Z turf at 1/2" will weaken the turf and promote a thin stand and weaken the root system. Scalping any bermuda (by going too long between mowings) causes the same problems, especially in the early spring.
Too early fertilizing can cause shrinkage of the roots, since stored food reserves is the roots are used with the fertilizer to make proteins for growth.
In early spring, the bermuda does not make a lot of food reserves, even though the leaves are green. This is why it is important not to mow to closely, start fertilizing too early, or verticut bermuda early in the spring. All three of these activities use up food reserves when the bermuda is not experiencing proper temperatures for adequate food storage to catch up from these activities.
As a guideline, you can mow regularly when the grass is 30% over the acceptable base mowing height. Fertilize bermuda in Phoenix the second week in April, with 1/2" lb. -N- per 1000 ft2 verticutting should be done later on in mid-May or June in irrigated bermuda. Add two weeks for Tucson, three for Globe and subtract three for Yuma.
High elevation turf - 4000 feet and above
Homeowners which have Kentucky bluegrass lawns get the early spring fever, even more! The KBG may be in a condition of being semi-dormant. In this condition, the KBG is green closer to the soil, but the leaf tips are half brown.
Wait until the half brown leaf tips extend past the desired mowing height (usually 2.0-2.5 inches), and then start mowing. When the daytime temperatures reach 75 consistently, that's a good time to fertilize with 3/4" -N- per 1000 ft2 from a complete fertilizer that has some N-P-K. A 3-1-2 or 4-1-2 ratio fertilizer is acceptable. Remember that in the spring and summer, cool season lawns don't make as many new shoots as in the fall. So don't push the lawn excessively with fertilizer. In generally cool season lawns benefit more from K+ (potassium) applications than bermuda. Verticutting of KBG for thatch reduction should be done in the fall! Increased weed invasion and low shoot densities which occur in the spring are two reasons for this. Also, summer is just around the corner and rooting conditions can be jeopardized by verticutting KBG in the spring.
Tall fescue lawns should be fertilized using the same guidelines as that of KBG. Rarely does tall fescue need dethatching, maybe once in 4-5 years (on heavy wet soils).
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.