Author:Geoff

A Lawn Retrospective on the Summer of 2023: Looking Ahead to the Fall Season

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Many lawns showed drought-stress symptoms in early summer. Photo: M. Talabac, University of Maryland Extension (UME)

It seems like ages ago, but during late spring and early summer we were in the midst of a long dry spell–and then things changed! Many areas in the region have seen more typical summer rainfall since late June. Since then, summer annual weeds and sedges were given new life with all of the wet conditions. For many homeowners, it has been a difficult summer keeping weeds like kyllinga, nutsedge, and crabgrass at bay during the wet, humid weather.  

Crabgrass and thin spots in a lawn. Photos: C. Carignan, UME

University of Maryland research (and others) has indicated that the best way to deter crabgrass is to mow higher. Experiment plots mowed in the 3.5-to-4-inch range have consistently had less crabgrass invasion than plots mowed at 2 or 3 inches. While this late summer weather has led to a lot of crabgrass and sedge invasion, homeowners can take solace in the fact that relief is in sight as far as the calendar is concerned. Late August/early September is the perfect time of year to re-seed with cool-season grasses like tall fescue to undertake a full-scale renovation or a lawn “rejuvenation.”

First, let’s define a few terms:

Complete renovation involves killing the existing sod to bare soil and re-seeding or installing sod.

Overseeding involves using an aerator or de-thatcher to open up the turfgrass canopy and then applying seed to increase density and sustain the stand. 

Repairing bare spots involves raking up old debris by hand or loosening it with a de-thatcher, then seeding.

More detailed information on these techniques can be found on the University of Maryland Extension Lawn Renovation and Overseeding resource page.

How do you decide what to undertake? If your lawn is thin, overrun with crabgrass, has a high percentage of broadleaf weeds, or is an otherwise “unsalvageable mess” you would probably consider a full renovation. If your lawn is a little weak in places, but otherwise dense and relatively healthy, overseeding would be more appropriate. Ensuring good “seed to soil” contact and maintaining adequate moisture in the seedbed is critical for successful germination.

Another key element in lawn renovation and overseeding is seed selection. There are a number of varieties (cultivars) of tall fescue available, however, some have performed better than others in the UMD evaluation trials and these are listed as “recommended varieties” in UMD Extension Bulletin TT-77-Recommended Turfgrass Cultivars (PDF). Although these varieties may be difficult to find at “big box” stores, many local garden retailers seek them out to stock them, and homeowners can often purchase them from local landscape professional suppliers or find them online at sites like seedsuperstore.com.

By Geoffrey Rinehart, Senior Lecturer, Turfgrass Management, Institute of Applied Agriculture, University of Maryland. Read more articles by Geoff.

Spring Lawn Care Tips

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A healthy, dense-growing lawn will do a better job of minimizing weeds and reducing erosion compared to a lawn that is thin and weak. For a variety of reasons, lawns can be challenging to grow in Maryland’s transition-zone climate. Turfgrass requires regular maintenance. Here are some steps you can take in the spring to keep it healthy, without resorting to “weed and feed” products. This series of videos is presented by Geoffrey Rinehart, Lecturer in Turfgrass Management at the Institute of Applied Agriculture, University of Maryland.

Mowing Tips to Prevent Weeds and Diseases
Winter Annual Weeds
Using Slow-Release Fertilizer

Early Spring Lawn Tips for Fertilizer and Pre-emergent Timing

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Speedwell is a winter annual weed. It will end its life cycle and die naturally once we have consistently warm temperatures. Photo: G. Rinehart

The warmer-than-normal weather during February had many people thinking about an early start to lawn and garden season. However, as temperatures have dropped and been below normal for much of March, it looks like we may have a couple more weeks before lawns really start growing. Lawn growth and crabgrass emergence are related to soil temperature, which is slower to change than the air temperature. While I have heard reports of soil temperatures topping out in the mid-50s for a day or two, it’s important to remember that in order to germinate crabgrass needs soil temperatures around 53-55⁰ F sustained for 5 days. These two things lead to a few questions, particularly pertinent this year when February felt like March and now March feels like late February.

Should I fertilize my lawn now?

While the legal window for applying fertilizer to lawns in Maryland began on March 1, that doesn’t necessarily mean you should fertilize your lawn just yet. Unless the grass is actively growing (which is dependent on warmer soil temperatures) it likely won’t take up and use the fertilizer—so you are better off waiting until the lawn is actively growing. Temperatures consistently around 60 and enough growth to warrant a second mowing are pretty good indicators of this. Keep in mind that if you fertilized your lawn in the fall you can probably wait until after the “flush of growth” in the spring (usually April/early May) and then schedule your spring fertilizer application for after that “flush” and leading into summer—usually around mid-late May. If you didn’t fertilize last fall it is tempting to try to “jump-start” the lawn in early spring with a fertilizer application, but hold off until the soil temperatures are consistently warmer and highs are around 58-60⁰ F on a regular basis.

Should I apply crabgrass pre-emergent now?

I would wait until soil temperatures are 53-55⁰ F sustained for 5 days. Keep in mind that your best defense against crabgrass is a dense turf that crowds out crabgrass seedlings. So, if you have good turf density and mow at 3” or higher, your overall crabgrass pressure should be lower anyway. The typical recommendation is to wait until the forsythia is “half green-half gold” (or even a little earlier), but with the warm February we had, that indicator may or may not be as accurate this year. You can check soil temperatures for your location at the following website: https://www.greencastonline.com/tools/soil-temperature. 

Is there harm in applying crabgrass pre-emergent too early?

Probably not, unless it’s applied several weeks early and the product starts to break down before crabgrass even starts germinating. If you want to maximize the period of time your crabgrass application is effective, wait until when conditions are conducive to crabgrass germination and then apply it.

grassy lawn weed called roughstalk bluegrass
Roughstalk bluegrass (Poa trivialis) is a cool-season weed that shows up in early spring. If you only have a few patches, you can dig them out by hand (including the roots) and overseed to fill in the bare spots. Photo: G. Rinehart

On another note, this is now the time of year when many winter weeds become more noticeable as they are likely producing flowers and setting seeds. While you can apply selective products to control these weeds, remember that these winter annuals like chickweed, purple deadnettle, speedwell, henbit, etc. are almost at the end of their lives and will die naturally once we have consistently warm temperatures. Another weed often noticed this time of year is the grassy weed called roughstalk bluegrass (Poa trivialis). Seeds of this grass are often a contaminant in turfgrass seed mixes (the cheaper the seed, the more likely you will have weed seeds) and this grass starts growing much earlier than tall fescue. As the temperatures warm, it is not as aggressive and noticeable. There are few selective control products that are labeled for roughstalk bluegrass and they tend to be restricted to professional sites and/or are expensive. If you only have a few patches in your lawn, digging these out (including the roots) and then re-seeding the spot with a soil-tall fescue mix is the best control approach for most homeowners.

By Geoffrey Rinehart, Lecturer, Turfgrass Management, Institute of Applied Agriculture, University of Maryland. Read more articles by Geoff.

The Time to Spring Seed Your Lawn is Now

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With springtime springing, many people are thinking about planting in their yards and gardens. While the best time of year to plant grass seed and renovate is in the fall, we have a narrow window in the spring that can be taken advantage of to try to fill in bare spots and thin areas. Thin or weak areas that may have been damaged over the winter or even last summer are very prone to crabgrass and other weed invasion as we get farther into spring and early summer. With cooler weather forecast later this week (many areas are predicted to have frost in the morning), we still have a good window over the next two weeks for spring grass planting. If you have already applied crabgrass preventer, then you’ll have to wait until fall to plant grass seed, but if you haven’t, now is a good time to try to “thicken up” some weak spots and create more density before weeds have a chance to get a foothold. 

While a “full scale” lawn renovation should only be done in the fall (unless you are using all sod), spring is a good time to rejuvenate thin or weak areas. To do this, use a hard metal rake to remove any dead plant debris from the area and expose the soil. Use a drop spreader or handheld spreader (larger area) or sprinkle seed by hand (smaller area) as you try to get good, even coverage of the area (for tall fescue seed you will want to have about 6-10 seeds/square inch seed density). You can then very lightly rake the area to get the seed worked into the soil less than 1/2″ or carefully step on seeds to ensure good seed-to-soil contact. Next, be sure to cover the seed by topdressing compost or peat moss over the newly seeded area. This will help the seed retain moisture until it starts to germinate and provide some protection from birds. Lastly, try to keep the new seed damp at least until germination. With our cooler weather and a few showers in the forecast, the upcoming weather will help with keeping the seeds moist until they germinate but you may have to do a little watering with your garden hose or sprinkler too. 

We don’t have a big window of time for spring seeding, but seeding now before crabgrass and other weeds become more active later in spring will help increase the density of the lawn and make it better able to resist weed invasion!

By Geoffrey Rinehart, University of Maryland Institute of Applied Agriculture

Summer Lawn Woes: Reasons Why Tall Fescue Grass Declines at This Time of Year

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It seems like a while ago, but it was only 5 weeks ago that we were experiencing a fairly gentle start to summer. We even had a few days in June with highs in the 60’s and it made for pretty easy lawn growing weather.

Flip the calendar to mid-July and it has been a different story. All of us knew summer would arrive eventually, and now we are dealing with high temperature and high humidity conditions very typical of mid-summer in Maryland.

For those with warm-season grass lawns, like zoysiagrass, the lawn should be thriving, as these grasses enjoy the heat. For most homeowners who have tall fescue, summer is always a challenge to minimize the heat stress and disease pressure on the lawn. Tall fescue is best adapted to growth when low temperatures are in the 50’s and highs are in the 70’s to around 80. Through July, we have had many days near or above 90 and many nights where the temperature didn’t drop below 70.

drought stress symptoms on tall fescue lawn
Drought stress symptoms appearing in tall fescue lawn. Drought-stressed plants exhibit a purple to grayish hue. Photo: Geoff Rinehart

There are a few different reasons your tall fescue lawn may be going brown or declining this time of year—the most common are related to drought stress, soils that are too wet, or brown patch disease. Typically, growth slows down a bit in mid-summer anyway as part of a grass’s natural growth cycle as it uses more carbohydrates (food reserves) than it makes. So when the grass does experience stress or disease it is slower to recover. Drought-stressed plants exhibit a purple to grayish hue, a narrower or “curled up” leaf blade, and footprints are visible for several minutes after walking across a drought-stressed area. Continue reading →

Q&A: Tire Gouges in a Lawn and Planting Grass After Construction Work

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lawn with tire gouges
University of Maryland Lecturer and Turfgrass Management Advisor Geoff Rinehart answers your questions about lawn care and planting. For more Maryland lawn care information, see the University of Maryland Extension Home & Garden Information Center website.

Q: I had a new shed put on my property. The delivery driver had to back onto my lawn. The weight of the truck and the flatbed put an initial 2-3 inch depression in the lawn. Where the driver had to pivot the trailer, the flatbed tires dug into the lawn 3-4 inches. In order to recover the contour of the lawn and deal with the gouges, what steps do you suggest I take? Today, after it rained all day, I went out on the lawn and attempted to press the humps down with my body weight and somewhat level the lawn back. I am worried, though, that the depressions indicate a serious compaction of the soil and damage to further propagation of the lawn.

Answer: You are correct – the gouges made by the flatbed have likely caused serious compaction to the area. You can try to press the gouges back into place and aerify now and topdress with ½” topsoil to try to smooth things out and see what happens next year. If you notice the area is struggling compared to the rest of the lawn and drying out more quickly if we have a dry summer, you’ll probably want to renovate the affected area by rototilling, re-grading, and re-seeding.   Continue reading →

Q&A: Japanese Stiltgrass Management and Lawn Fertilization Tips

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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?

Japanese stiltgrass in a lawn

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.  Continue reading →