The Hampton Gardener


Lawns all over are greening up and in early spring even the worst of lawns can look great. But how did your lawn look last July? Was it choked with crabgrass? When the first frost hit the area, did your lawn turn to a straw color and half the density disappear?

It’s time to get that crabgrass under control and now’s the time to take action!

Unfortunately for many of you, that will mean the use of a chemical pre-emergent herbicide. That’s an herbicide that kills selected plants (in this case crabgrass) as the roots begin to break the dormant seed coats. This breaking of dormancy in crabgrass seed is both moisture and temperature dependent and we can almost tell to the day when this will begin, but for the sake of making life easy we generally apply this herbicide when forsythia shrubs are at or just past peak bloom. This generally happens in early April, but it can vary by as much as a week from Westhampton (early) to East Hampton (later).

Crabgrass, like kudzu, purple loosestrife and the gypsy moth, came to our shores with good intentions, but quickly became obnoxious and unwanted. At the turn of the century it was introduced as a miraculous grass for forage, a high quality summer diet for grazing animals, and it’s still popular in the South and Southwest.

The rest of the story is in your yard.

It would be fine if crabgrass had redeeming qualities in 2008, but it has none. It grows in bunchy patches forming a loose, spotty type of lawn and it’s only green from May through October and then turns as brown as Zoysia with the first frost. By the next spring, the lawn with crabgrass is merely large areas of bare soil surrounded by the dead carcasses of last year’s plants permitting erosion from the spring rains and leaving large open spaces for new crabgrass seed to germinate.

But hear this: YOU CAN GET RID OF THIS WEED. And yes, there are organic crabgrass controls, but your timing is critical, as is persistence. Remember that this is what we call a hardy annual plant. It grows from seeds left from last year’s crop, matures during the summer, sets seed again and guarantees another crop for next year unless you play some well-timed tricks. The most important of these tricks is to apply an herbicide called a pre-emergent which kills the seed just as germination takes place, while not harming your other grass plants.

These pre-emergents are generally applied as granulated products and they can be applied alone or in conjunction with the first application of lawn fertilizer, which isn’t necessarily good. I belong to the school that says the first feeding should be later in the season. Therefore, you need a spreader and the product must be applied just at the right time to catch the seeds as they break dormancy and as long as the soil isn’t disturbed it remains at the soil surface for eight to 12 weeks (depending on the product used) creating a barrier that catches any latecomers. Now how can you possibly know when this happens? It’s pretty simple. Watch the forsythia. As the forsythias flowers just begin to fade and pass their peak, crabgrass is just beginning to germinate. Make your pre-emergent application at that point and possibly one more time next year and you’ve got it pretty much licked. You can then take a year off, evaluate your lawn in the off year and then, if necessary, repeat the application the following spring. It’s rarely necessary and in fact it can be detrimental to your lawn to make applications every single year.

For extra insurance, some people will apply a post emergent herbicide specifically for crabgrass later in the summer when any missed plants that show up can be killed before they set seed. Here again, timing is critical because if you wait too long and the seed is set, all of your work to this point will be wasted. Most of these post emergents are sprayed on and used as spot treatments where crabgrass plants show up. Simple? The post emergent applications are generally done with a liquid and only spot treatments are necessary, not an application over the entire lawn.

A few things to consider along the way: If your landscaper offers to kill your crabgrass in August or September, fire him. The seed has already been set and the effort will be useless other than to line his wallet. If you are going to do any seeding of your lawn this spring, the majority of pre-emergents can’t be used as they’ll stop your grass seed from germinating. However, a product called Tupersan can be used since it won’t affect grass seeds. Tupersan is short lived though, and a second application should be made six weeks after the first. My advice is to wait until fall to seed and get the crabgrass under control now. In some cases you may want the services of a certified pesticide applicator (like your lawn service or gardener), but most products can easily and safely be used by following the label directions.

For organic gardeners, there are a number of branded products that contain corn gluten, which has been shown to be an effective crabgrass control. Corn gluten has to be used with some foreknowledge though because it isn’t as straightforward as the chemical controls. First, it will take about three years to get control of crabgrass with these products. Each successive year it seems to become more effective and by the third year of application it will result in 95 percent control. Any errant plants that show up that summer can be hand weeded. Second, corn gluten contains a certain amount of nitrogen, so you need to remember to cut back on your fertilizer program. About 10 percent of your lawns nitrogen needs will be satisfied with this natural herbicide. Lastly, corn gluten herbicides are expensive, but remember you are also cutting down on the use of fertilizers and some gardeners are willing to pay the price to eliminate chemicals from the lawn.

Now here’s two other critical pieces of information. A tightly knit and healthy lawn is your best defense against crabgrass. If the grass is spotty and patchy those open spaces are like crabgrass invitations. In a thick lawn, crabgrass can’t get enough light to germinate. The tie in here is that you can have a thick and healthy lawn and reduce your fertilizer use by 50 percent. Many lawns need as much as 3 to 4 pounds of nitrogen-based fertilizer a year to remain lush and green, which translates to resisting weeds and diseases. But if you use a mulching blade on your mower or insist that your lawn service leaves the lawn cuttings behind fully half of the lawn’s nitrogen needs will be supplied by the returned clippings.

And nitrogen, supplied via chemical fertilizers, is extremely dangerous to our ground water and surface water when it reaches ponds, streams and bays and our groundwater.

So, watch the forsythia, plan your attack and get that crabgrass under control. Keep growing.

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