Initial Mowing of Kentucky Bluegrass‐Perennial Ryegrass Seedling Turf Mixtures1

Abstract

Mixtures of turf‐type, perennial ryegrass (Lolium perenneL.) and Kentucky bluegrass (Poa pratensisL.) are desirable for lawn plantings because they combine a uniform appearance with genetic diversity. Attaining a balanced mixture of these two grasses is difficult because of the vigorous seedling growth of ryegrass, relative to blue‐grass. The purpose of this study was to evaluate the effects of close mowing of a Kentucky bluegrass‐perennial ryegrass seedling stand on the establishment and development of the turf. A field trial was established which contained mixtures and monocultures of both species, planted on Hagerstown silt loam (a fine, mixed, mesic Typic Hapludalf) in University Park, Pa. Kentucky bluegrass was generally more prevalent where close mowing treatments were used shortly after emergence. After 2 months of growth, a stand seeded at 95% bluegrass (pure‐live‐seed count) contained 49% bluegrass shoots when mowing began on Week 3 (the 3rd week after sowing) at a height of 3.8 cm, 66% bluegrass when mowing began on Week 3 at 1.3 cm, and 84% bluegrass when mowing began on Week 2 at 1.3 cm. Kentucky bluegrass was optimally favored by the commencement of mowing at 2 weeks after planting (approximately 9 days after the first noticable emergence of the ryegrass). This date coincided with a 50% foliar ground cover in the unmowed, mixed stand. Plots mowed initially at 3.8 cm required at least 95% Kentucky bluegrass in the seed mixture to produce a 50:50 mixture of the two species at 2 months. Plots mowed at 1.3 cm, 2 weeks after planting, needed only 50 to 75% bluegrass seed in the mix to achieve the same result. The shoot density, shoot size, and the leaf area index (LAI) of Kentucky bluegrass in mixed stands tended to decrease with an increase in the initial height of cut and/or the weeks until first mowing, while the density and size of perennial ryegrass shoots tended to increase. No observable injury (e.g., discoloration or scuffing damage) was caused by the close, early mowing treatments. Monocultures received no appreciable benefits from the close, early mowing treatment. Mowing of monocultures should begin as soon as the seedlings exceed the height intended for the mature stand.