University of Maryland Lecturer and Turfgrass Management Advisor Geoff Rinehart answers your questions about lawn weeds and fall fertilization.
Q: What is this “grass” and is it possible to eradicate it from our lawn? It has been spreading down the hill from our neighbor’s property. What’s the best way to bring our lawn back to a nice quality grass?
Answer: Japanese stiltgrass (Microstegium vimineum) is an invasive summer annual grass that is becoming more pervasive in Maryland. While it used to be more limited to just woodland areas, we are getting more reports of it infesting lawn areas in recent summers.
As is the approach with any weeds, practicing good turfgrass cultural practices to encourage a healthy, dense stand of grass is the cornerstone of any lawn management program. Mowing taller (3”-3 ½”), fertilizing based on University of Maryland recommendations, and overseeding annually with improved turfgrass cultivars are three practices that will help create greater density.
This summer has been a particularly difficult one for controlling summer annual grasses like crabgrass, goosegrass, and, of course, Japanese stiltgrass since these weedy grasses are favored by wet, hot conditions like the weather we had in July-September. Since Japanese stiltgrass is a summer annual, it can be deterred by applying a pre-emergent herbicide in the spring at forsythia bloom (which is a similar approach to crabgrass control). When watered-in, pre-emergent herbicides form a soil barrier to seed germination. However, most of these products only last 6-10 weeks (the lower part of this range when it is wet and/or hot, the upper part when it is dry and/or cool). This May was rather rainy, so if you applied a pre-emergent in early April, another should have been applied in June. Usually, two applications are enough to get us to early August and then summer annual weed pressure decreases as early cooler weather is usually a month around the corner.
This year, the second half of the summer has been wetter and continued warm, which has really favored summer annual grasses. Proper pre-emergent applications at forsythia bloom and early June coupled with sound turfgrass cultural practices should help to reduce the effect of this weed. We still have a small window to re-seed and overseed areas that have been taken over by summer annuals. You can remove the weeds, open the ground up to bare soil, then seed, apply starter fertilizer, and cover with compost or peat moss to help keep the moisture in.
Q: My lawn is three years old and I would like to apply a fall fertilizer to prepare it for winter. I have read online that a good fall fertilizer would be 13-25-12. Do you agree and what fertilizer would you recommend to give me good root growth and prepare the lawn for next year?
Answer: The lawn analysis numbers stand for the percentages of nitrogen, phosphorus, and potassium (N-P-K). New seedlings need a little more P to grow and usually “starter” fertilizers have a higher P number. Unless a soil test indicates that your lawn is deficient in P, you should avoid applying more (i.e. choose a fertilizer with “0” as the middle number). Potassium is important for stress tolerance and helping with winter hardiness so ideally, you would apply a “winterizer” fertilizer where the N and K (1st and 3rd) numbers are about the same. The recommendation would be to apply 0.9 lb. of nitrogen/1000 sq. ft. now in early-mid October then a similar application between November 10-15.
Fall Lawn Fertilization
Fall is the best time of year to fertilize cool-season lawn grasses like tall fescue. The University of Maryland recommends two applications of 0.9 lb. of nitrogen/1000 sq. ft. between September 1 and November 15, preferably 4-6 weeks apart. If you made a fertilizer application in September you should make another between now and early November. If you haven’t fertilized yet this season there is still time to fertilize now in mid-October and again before November 15. Fertilizing now will help stimulate root development and prepare the lawn for a successful spring and summer next season. Find more information on proper techniques for fertilizing lawns on the Home and Garden Information Center website.
Lawn Care Workshop
I will be teaching a 2-hour fall lawn care workshop at the U.S. National Arboretum from 10 a.m.-12 p.m. on Saturday, October 20. This will include a classroom presentation about lawn best management practices and a tour of the ‘Grass Roots’ exhibit on site. Registration is free. For more information, please contact me at email@example.com.
By Geoff Rinehart, Lecturer, Turfgrass Management, Institute of Applied Agriculture, University of Maryland.