crab grass

Sun Jul 04, 2010 7:17 pm

around the garden is a lot of crab grass. what do you-all recommend to eliminate crab grass, but not burn the grass itself.

Thanks, Todd

Re: crab grass

Sun Jul 04, 2010 8:04 pm


Your best approach for crabgrass control is preemergent herbicide applied early next spring. After the crabgrass is well established, your control options in turf are few and don't work that well. Crabgrass begins to germinate when 50 to 75 Growing Degree Days (GDD) have accumulated (here in Ohio that is when Forsythia begins to bloom). Crabgrass germination peaks at 175 to 200 GDD. Here, in Ohio, excellent control is achieved when a weed and feed product is applied to the turf when the forsythia just beginning to bloom.

This is a U of Mn publication that may help. You can contact your local (right in your backyard) office of Minnesota Cooperative Extension here:
UM Ext Blue Earth Cnty
204 S 5th St Ste 310
PO Box 8608
Mankato, MN 56002-8608
(507) 304-4325 (phone)
(507) 304-4059 (fax)

The following is a newspaper article I prepared for publication this spring:

Master Gardener News Herald Article
May 2, 2010

Spring Got Here Early by Bill Hudson

Spring arrived early, almost two weeks early, at my house. Caught flat-footed, my application of weed-and-feed was later than optimum, so I am expecting to see an increase in the amount of crabgrass I will have to deal with this summer.

This leads to a question that is important for understanding crabgrass, a very troublesome weed in home turfgrass, and its effective control. If the calendar is not a reliable determinant of when to apply crabgrass control herbicides, what can be used to effectively predict the timing of this application?

For years, the calendar has been used to recommend windows of time for application of various products used in lawncare and other horticultural activities. While very useful, the calendar does not control the environment nearly as well as it controls us. For comparison, in 2008, my first mowing was April 14, in 2009; my first mowing was April 17. This year, April 4 was the first mowing, fully 10 and 13 days prior to the previous two years.

As for the application of the weed-and-feed, I made timely applications in 2008 and 2009 on April 18. This year I was late when I made the application on April 6. In all three years the calendar would say that my applications were timely. Why would I say that I was late this year? Because I was not paying close attention to landscape plants that signal particular events. Specifically, forsythia was in glorious bloom when I applied the weed-and-feed and 99 Growing Degree Days (GDD) had accumulated by the time I made application.

What is a GDD and why look at the forsythia bloom? GDD is a measure of accumulated heat units determined by mathematical calculations based upon temperature. The basis for the calculation is not important, for this discussion, however, the number of GDD is. As for the forsythia, bloom begins when a specific number of GDD have accumulated. Together, a specific action by specific plants are related to specific GDD and is called a phenological calendar.

What this all means is that crabgrass begins active germination between 50 and 75 GDD and reaches peak germination between 100 and 200 GDD. Early blooming (Northern Lights) forsythia begins to bloom at 55 GDD and reaches full bloom at 94 GDD. The day I applied the weed-and-feed, 99 GDD had accumulated. Although I had beat the peak germination, by very little, I still needed a good rain to water the chemical into the soil to be effective. Bottom line, I was late and cannot expect excellent control because the already germinated crabgrass will not be controlled, only the crabgrass germinating in the presence of herbicide in the soil will be controlled.

Spend some time surfing the Ohio Agricultural Research Development Center (OARDC) Growing Degree Days and Phenology for Ohio website at to learn more about this very useful tool.

For those asking themselves, does he really know the dates he mows his lawn and applies different products to it? Yes, I do. Spreadsheets are marvelous tools. And, no, you don’t want to know how many times I mow my lawn each year.

Interested in scheduling a speaker or learning more? Call the Lake County office of Ohio State University Extension at 440-350-2582 or stop by our office at 99 E. Erie St., Painesville, Ohio 44077-3907, to arrange the schedule. More information is available at

Good luck.


Re: crab grass

Mon Jul 05, 2010 12:11 pm

very good reply. Thank you. I'll have to watch the yellow forsythia next spring. For the areas I'm looking at Round-up may be the best.


Re: crab grass

Mon Jul 05, 2010 12:20 pm

Todd - I use a pump up sprayer with round-up. I have even cut the bottom out of a 2 liter bottle and stuck my wand through it and taped it on. Works great for spraying close to plants. Remember all it takes is a drop on the plant.


Re: crab grass

Fri Jul 16, 2010 2:05 pm

If you want to go organic think about corn gluten meal. From the University of Minnesota:

Corn gluten meal (CGM) is a natural substitute for synthetic pre-emergence herbicides. Pre-emergence herbicides attack seeds while they're still in the ground, before the seedlings emerge from the soil. CGM is a by-product of commercial corn milling that contains the protein fraction of the corn. Its use poses no health risk to people or animals. In fact, because it is 60% protein, corn gluten meal is used as feed for cattle, poultry, fish, and dogs. In addition to the 60% protein, corn gluten meal is 10% nitrogen, by weight.

The use of corn gluten meal as an herbicide was discovered during turfgrass disease research conducted at Iowa State University. CGM was observed to prevent grass seeds from sprouting. Further research has shown that it also effectively prevents other seeds from sprouting, including seeds from many weeds such as crabgrass, chickweed, and even dandelions.

Corn gluten meal is effective only against seeds, not existing plants. Annual weeds that are already up and growing will not be killed by products made of corn gluten meal. They'll die on their own, though, by the end of autumn. But most of the seeds they produce later in the season shouldn't sprout - provided you've applied the CGM properly and at the correct time. Crabgrass, foxtail, purslane, and prostrate pigweed are examples of annual weeds found in lawns.

Existing perennial weeds such as quackgrass, plantain, and dandelions won't be damaged by CGM, either. And, they'll still come back from one year to the next because their roots survive most winters. What corn gluten meal will do is stop the seeds they shed each summer, so the population of these particular weeds won't increase. In fact, because some will die of "natural" causes, their numbers should actually decrease after several years of consistent CGM use.

Here's the link

Re: crab grass

Sat Jul 17, 2010 10:49 am

Crabgrass seed germinates at 52 deg.+- one degree. So you can take the temperature of the ground or watch the forsythia which blooms at the same temp.

Re: crab grass

Sat Jul 17, 2010 7:44 pm

I applied the Scotts with crabgrass preventer on March 19 this year. I have it coming up all over the yard now. I am very dissatisfied with thier product.
Could it be that we havent had rain and the temps have been above 100 ? Most of the rest of the lawn is in a bad way. Could it be that a new strain has become immune ? I dont know .

Tired of wasting money on grass that doesnt work

Re: crab grass

Sun Jul 18, 2010 11:50 am


A few quick questions, although short questions, the answers are critical:
How many thousand square feet of lawn do you have? (this is not to be a guess, requires actual measurement)
How many bags of Scott's did you use?
How many thousand square feet was each bag to cover?

I ask these questions because these are common problems. a couple of cases to illustrate:

A good friend complained because his crabgrass prevented did not work the previous year. Before going to his home I looked up his property on the web and found that he had 2.03 acres. Looking at the aerial view, woods covered half of the property and his home site the rest. After accounting for the house, landscape beds and driveway he had probably three quarters of an acre of lawn. Three quarters of an acre is 32,670 square feet, or for easy calculations, 33 thousand square feet. He had already applied his 'weed-n-feed' because he was leaving for the Carolinas for his annual week-long golf retreat with his friends. I asked how much he had applied. "Three bags." How many thousand square feet was each bag to cover? "5" So a little fast calculation (without the aid of pencil, paper or electronic device of any kind) revealed that he was applying less that half the product needed to control the crabgrass. (This is not uncommon.)

Another fellow called the office because his grass was 'dead.' He had recently applied fertilizer. After several questions we determined that his small yard had roughly 1000 square feet. How many thousand square feet was the bag to cover? "5" How much of the bag did you apply? "All of it." Five times the amount of fertilizer needed, burned the grass. (Over-application is also a very common problem.)

So, Russ, knowing precisely how many thousand square feet of lawn you have is critical. The bottom line is that the most effective herbicide (or other pesticide) will not work if applied:
at the wrong time
in the wrong amount (more is not better)
or unevenly applied

Scott's (as all manufactures of lawncare products) make products that will work when used as directed. Operator error is responsible for the vast majority of cases when the product doesn't work.

Hope this helps.


Re: crab grass

Sun Jul 18, 2010 1:25 pm

Hey Bill thanks for the reply. I own 1 acre but dont know exactly where the lines are. I am against the woods so have pushed back the lines back.
Any way, I buy 3 bags of product that covers 15,000 sq ft each. The spreader is set as directed on the bag and use the recomended width per pass.
There is usually some left over that I run off on the neighbors dandelion patch.
Any way its over until fall for an overseed. Thanks for the help.


Re: crab grass

Sun Jul 18, 2010 4:24 pm

Russel hit this one on the head. All you need to know is on the bag. As always, follow the directions to the letter. I don't buy Scotts but rather the same stuff from the farm supply.