Too Late for Crabgrass?

The best way to control crabgrass is to kill it before it grows with a pre-emergent herbicide, but when is it too late to treat? Unfortunately, there’s no single definitive answer to this question. The short answer is to apply it before the crabgrass has a chance to germinate. The longer answer is that it depends on the weather and which pre-emergent is being used. Pre-emergent herbicides work by creating a chemical barrier that kills the crabgrass when it germinates. Some pre-emergent products provide some post-emergent control as well. Determining when a seed germinates depends on many variables in the environment. For crabgrass, the biggest variable is temperature. Crabgrass only germinates at sustained soil temperatures above 57°F at a one-inch depth. The best way to track the soil temperature is with growing degree days (GDD). Because it is tough to track soil temperatures without specialized equipment, we can use air temperature. Air temperatures will usually need to be at around 50°F for 200 degree days for germination.

200 days! That sure seems like a long time! That’s a common misconception that sometimes even confuses our office staff, but GDD isn’t just based on a calendar. GDD is based on a formula calculated by monitoring the median temperature. When the median temperature (High plus low divided by 2) for a day is above the range needed for germination, the number of degrees above that point is added to the GDD. For example, if the air temperature is at 52°F one day, 53°F the next day, and 49°F the day after that we have 5 GDD for that time period (there’s no such thing as negative degree days because plants can’t un-grow). It’s important to remember that areas in full sun or next to pavement will be warmer, and areas in the shade will be cooler than the average, so you have to take that into account with your own lawn.

(GDD Formula1)

All this math is a major pain just to find out if it’s too late to apply your pre-emergent crabgrass control. The rule of thumb that many landscape professionals used to go by was when the forsythia starts blooming. These days we have meteorologists help us out. To track the GDD yourself go to and follow these steps2:

  1. Enter your zip code (not all locations are included, check nearest weather station to your site) and hit enter
  2. Click the “custom” tab/button below the date
  3. Enter the start date below the word “from” (ex. Jan. 1) and the end date below the word “to” (current date)
  4. Hit the get “history” button
  5. Read your growing degree days (base 50) in the ‘Sum’ column (=Cummulatlive DD to date for the year)

Of course, the easiest way to make sure your pre-emergent crabgrass control gets applied on time is to call MRW Lawns at 301-870-3411 and let us take the work and worry out of having a real wonderful lawn.




P.S. If the growing degree days are over 200 in your area, don’t panic! There are post-emergent products that can help control crabgrass, even when fully grown; and in the worst-case scenario, crabgrass is an annual weed, so you’ll get another crack at it next year!

Should I seed my lawn this spring?

We get questions about spring lawn seeding every year. Many people, especially grass seed producers, recommend it, but it may not be the best option. While we can aerate and overseed in the spring, we recommend waiting until the fall for two main reasons. First, the weather in the spring and summer is challenging to seed and new grass. The spring weather can be unpredictably warm or cold, and grass seed needs soil temperatures for germination that are far from guaranteed. Additionally, the grass is in the early stages of growth during the heat of the summer, leaving it susceptible to disease and heat and drought stress. For these reasons, spring lawn seeding is less successful than fall seedings. The second reason is weeds, namely crabgrass. Crabgrass is the most important weed to control throughout the lifetime of the lawn, especially in the first few years of treatment. Because of this, our first application of the year includes a pre-emergent crabgrass control which stops the crabgrass seeds from sprouting by creating a protective barrier of herbicide that kills the crabgrass before it can reach the surface of the soil. It also prevents desirable turfgrass from sprouting, making seeding and crabgrass control almost mutually-exclusive. (more…)


The weather man is calling for BEAUTIFUL WEATHER! over the next several days. Sunny skies with no rain in sight for the near future. While you are making your plans to take advantage of the sunny skies, don’t forget to give the lawn some attention. It will need some water from you. Go to our website and review how to best take care of the lawn as the soil water bank starts to dry up. (more…)

Just in Time for Christmas! MRW Lawns Gift Cards Now Available!

When your friends and family ask you what you want for Christmas, tell them to buy you the Gift of GREEN this holiday season! MRW Lawns, Inc. is now offering gift cards. With an MRW Lawns, Inc. gift Heart of Grasscard, you can purchase valuable services like lawn fertilization, weed control and pest control for the outside of your home. This gift card can be used for existing services as well as new services. Regular treatments are a sure way to create a beautiful usable outside space for entertaining friends and family on those long holiday weekends or anytime. They help create a safe environment for the kids and the family pets, free of weeds and harmful insects. (more…)

It’s a Beautiful Day!

It’s a beautiful day here at MRW Lawns, Inc. The low humidity and nice temperatures allow for some good drying after the torrential storms on Saturday. Enjoy it while it lasts, and be sure not to let the lawn get too tall. Now, it is important not to mow when the soil saturated, but try not to let it get too tall, and mow it twice if you have to to remove excess growth (for example; the lawn gets to 7″ and you want to mow it to 3″). (more…)

How to Manage Your Lawn During Hot Summer Weather

1010012_10152300723320016_1466405545_n[1]If there is one thing we can count on here in Washington DC, it is the hot summer weather periods we experience every year in summer. Don’t let it get the better of your lawn. Go to our website today at and read our Summertime Tips under the Seasonal Tips menu. This will guide you to do the right things during the tough times this summer. As always, feel free to call if you have questions or need assistance.