David M. Kopec, Extension Turfgrass Specialist
Mid-High Elevation Areas
This includes areas like Globe, Sierra Vista, Winslow, Kingman, etc. These areas are capable of growing either bermudagrass or cool season lawns all year round.
Mid Elevation Lawns
(Non-overseed Bermuda, Zoysia, St. Augustine -- warm season grasses)
These grasses will show evidence of greening up at the beginning of the month and will be already green on south facing slopes and by heat absorbing surfaces. Avoid the temptation to jump start these grasses at this time by putting on large amounts of nitrogen fertilizer. If you feel that you must have an early green lawn, apply iron to the leaves once 75% of the lawn is green (see last months issue). Research has shown that St. Augustine and Zoysia can be damaged by forcing growth too early into spring when the soil is still cold and the roots are not functioning at "summer" capacity. By April 1-10, you should have applied a pre-emergence herbicide for controlling crabgrass, southwest cupgrass, stinkgrass and spurge. There are many safe products available on the market which include Treflan, Balan, PR-EM (and its many forms) Dimension, Barricade, etc. Do not verticut the thatch on warm season grasses at these elevations until June. You will damage the lawn and invite weed trouble. Fertilize mid-elevation warm season grasses starting in May.
(Kentucky, Bluegrass, Tall Fescue, Perennial Ryegrass, Fine Fescue
-- cool season lawns)
April is probably the best month for lawn growth for these grasses at the mid-elevation areas. Apply a complete fertilizer on the lawn (contains N-P-K) at the rate of 1.0 lb. -N- per 1000 ft2 of lawn area in April. Do not apply nitrogen at higher rates than this. Even though it will make the lawn grow faster, you can actually decrease spring rooting, which is important for summer survival later on.
Early April is a excellent time for aerifying the lawn, by poking holes in the lawn with an aerifying machine, or pitch fork. Aerifying is not verticutting, which should not be done on cool season lawns at this time. Verticutting can seriously damage the lawn at this time. After aerifying in early April, leave the holes open. You do not have to fill them with sand. If you wish, you can topdress the lawn with a thoroughly composted manure product and sweep or drag it into the aerifyer holes. It's smart to aerify before the fertilization.
High Elevation Lawns
(Kentucky Bluegrass, Tall Fescue, Perennial Ryegrass, Fine Fescue -- cool season lawns)
High elevation areas like Flagstaff and the White Mountain areas grow cool season grasses all year round.
In the last week of April, a pre-emergence herbicide can be applied to the lawn for control of grassy weeds before they come out of the ground. A post emergence herbicide (phenoxy-type) can be used to control perennial broadleaf weeds at this time (dandelion, some thistles, clovers, etc.). Note that these weeds may need to be treated again in the fall. Flagstaff and the White Mountain areas can follow the same maintenance practice listed for April, but move them back one month later into May, favoring mid or late May at the highest location areas.
Note that lawns which are 95% or greater Kentucky bluegrass can be lightly verticut in the spring when 85% of the lawn is green. If the lawn contains an appreciable amount of perennial ryegrass, the lawn can be damaged. In lawns that have a lot of perennial ryegrass mixed with Kentucky bluegrass, you are much better off dethatching (verticutting) in the fall, followed by partial re-seeding. Dethatching to remove thatch on a KBG lawn is better done in the late summer or early fall.
Low Elevation Lawns
(Overseeded bermudagrass, permanent Fescue Lawns)
April means excellent growing conditions for these lawns. If you used ammonium fertilizers all winter long, you are now ready to witness the "ammonium" bloom on your lawn. When the soil gets warm in the spring, the ammonium changes to nitrogen, which the grass picks up readily. Thus, lots of stored ammonium can change quickly to nitrate -- and you can watch your lawn grow, or overgrow. You must now mow more frequently and/or raise the mowing height. Some bermudagrass may be starting to show up in the lawn, but its still to early to drive out the ryegrass at this point.
For tall fescue lawns, fertilize the lawn with ½ - 3/4 lb. -N- per 1000 ft2 the first week in April. That should be it. Spray iron after mid-April to make the lawn green. Stay on a regular mowing program (frequency and height) in the spring. Avoid scalping the lawn. On fescue lawns, it's good to aerify the lawn the first week in April at the low elevation locations.
(Non-overseeded Bermudagrass, Zoysia, St. Augustine -- warm season
Bermudagrass will be green in April, while Zoysiagrass and St. Augustine will be slower to green up. Do not dethatch any of these grasses until May 15 for bermudagrass and June 1 for Zoysia or St. Augustine. All three of these grasses may show iron chlorosis symptoms at green-up, since the soil temperature may still be low. Apply iron. Zoysia and St. Augustine in the shade will be slower to green up. Resist the temptation to fertilize the Zoysia or St. Augustine lawn until the grass in the shade has completely greened up.
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.