You Are Here: Management Updates 2000 Archive September 12, 2000

Date: September 12, 2000
Category: Agronomy
Subject: Fall Turf Maintenance

Weather conditions this summer have been unusually cool with above average rainfall which have been extremely kind to cool season turfgrasses like Kentucky bluegrass, perennial ryegrass, tall fescue, and fine leaf fescue. Drought stress injury (dormancy) has not been observed even along roadside areas. Grasses in such areas have been actively growing all summer. Turfgrass will benefit from fertilization in early to mid-September to maintain active growth and encourage the production of new tillers and lateral stems (rhizomes and stolons) that will increase turfgrass density. Late summer/early fall fertilization will be important in maintaining good color throughout the early to mid-fall period until a follow-up fertilization is made in late fall. September fertilization is critical to the success of late fall applied fertilizer to encourage rooting and storage of carbohydrates that will help in winter survival. Now is a good time to fertilize at 0.9 to 1.25 lb N/1000 sq ft derived from all water soluble nitrogen sources (urea, ammonium nitrate, ammonium sulphate) or using nitrogen with 25 to 50% dervived from slow release sources (sulfur or polymer-coated urea, IBDU, urea formaldehyde products, or natural organics). In the absence of a soil test, fertilizing with a nutrient ratio of nitrogen (N), phosphorus (P2O5) and potassium (K2O) of 4-1-2 or 3-1-2 are recommended. Examples of fertilizers with this N- P2O5-K2O ratio would be 20-5-10 or 16-4-8 (4-1-2) and 15-5-10 or 12-4-8 (3-1-2).

Fertilizing following core aerification will help incorporate fertilizer phosphorus into the root zone and the added N will promote rapid recovery from aeration events. This is an ideal time for aerifying soils because early fall is a period of peak shoot growth, so grasses quickly recover from coring. Most drum type aerators used by landscapers and lawn care operators will require at least two passes over the lawn to pull enough soil to achieve the desired effect (reduce compaction, modify thatch, or to prepare a partial seedbed for overseeding). The warm soil of late summer-early fall will promote rapid germination of over-seeded grasses and is a time of minimal weed seed germination affording superior grass survival and establishment. The use of a 1-1-1 type fertilizer ratio (19-19-19 or 10-10-10) would be recommended at the time of overseeding established lawns.

Perennial ryegrass blends work best for overseeding already established lawns because of its aggressive juvenile phase. Slow germinating species such as Kentucky bluegrass (and fine leaf fescue) may not necessarily survive to maturity because of its weak juvenile characteristics. Kentucky bluegrass as an over-seeded grass work best when the existing turf has been partially suppressed by close mowing (scalping prior to seeding) or when seeded following total eradication of the exiting grass cover using a non-selective herbicide. It is best to delay or postpone fertilizing suppressed turf until the bluegrass has germinated. Otherwise, only the already-established grassy cover will respond to fertilization at the expense of the slower-growing Kentucky bluegrass.

- Submitted by: Dr. Scott Ebdon