The BEST source says it's time to kick back your crabgrass
Madhuri from Chantilly writes: "Crabgrass has been my main lawn concern for many years now. I know you recommend using corn gluten meal as a crabgrass-preventing pre-emergent just as the ground temperature reaches 55 degrees. Are we there yet?"
It's not the temperature at ground level that determines the optimum time to apply a pre-emergent herbicide, Madhiri — it's the soil temperature, which is measured four inches down. Unfortunately, the experimental station that normally reports those temps for the region (and upon which I've been relying for years) has been out of operation for several months, and it's the only one I've been able to locate that reliably measures the soil temperature in our area.
Now, the local water temperatures — which almost exactly mimic the soil temperatures — have suddenly risen from 38 degrees and 40 degrees last week into the high 40s and low 50s as of Thursday afternoon. And that's exactly what happened a week before soil temps hit 55 last year.
But I want to be SURE. And since there's only one truly impeccable source of knowledge and information, it's time for me to consult it. Silence please, while I ask the question aloud: "Is this the right weekend to apply corn gluten meal to D.C.-area lawns?"
And the Magic 8-Ball says…
That settles it. Get your gluten down!
Timing + wetness + dryness = killed crabgrass
Wendy in Rockville writes: "My forsythia are blooming, so I'm getting ready to spread corn gluten meal on my lawn. But I read in one of your columns that it's not a good idea to put it down when you know it's going to rain. It is supposed to rain over the weekend. Should I put it down? Or wait longer?"
The blooming of forsythia and redbuds is yet another sign that soil temps are approaching that magic number of 55 degrees, and beating the germination of all those dormant crabgrass seeds in the soil trumps any other aspect of timing.
But corn gluten meal prevents the most crabgrass when its applied to dry soil, thoroughly watered and then allowed to dry out.
The forecast is for really nice, dry and warm weather Saturday and Sunday, perfect for application. Then there's an excellent chance of rain on Monday (80 percent as of Friday morning). So the smart money says to apply the corn gluten over the weekend, let Nature wet it down and then hope that the long-range forecast -- which calls for nice weather afterwards -- is correct.
And you'll still prevent a lot of crabgrass even if it does get a little wet again after that.
The only thing you can really do wrong is delay
Yes, another one! (And I've got lots more. The corn gluten emails came pouring in on Thursday afternoon.)
Terry in Silver Spring writes: "I saw some forsythia blooming today, so I'm thinking that it's time to put corn gluten down. Am I correct? I don't want to misjudge this most time-sensitive lawn chore."
Right you are, Terry. To prevent your dormant crabgrass seeds from germinating, corn gluten meal should be applied to your turf just as soil temperatures approach 55 degrees, which they certainly seem to be doing by all indicators.
And it's always better to be a little early with this lawn chore than a little late. The natural pre-emergent action of corn gluten meal lasts six weeks. And NO pre-emergent -- chemical or natural -- can negatively affect weed seeds after they germinate, so this weekend would seem to be the ideal time to get your gluten down. The corn gluten will stay strongly active through the entire month of April, which is when crabgrass seeds always germinate in our region.
And again: You snooze, you lose. If you wait too long, any weed and feed becomes feed for the weeds.
Getting your lawn off drugs
Hilton in Upper Marlboro writes: "My 'full service' lawn care provider has been unable to achieve anything close to a weed-free, green turf, so I've decided to take your advice and 'get my lawn off drugs.' I will do the weeding and feeding and have the service just cut and trim. Can you provide an annual routine for this process? I have tall fescue grass."
Sure thing, Hilt. As we have explained in depth above, apply 9 to 10 pounds of corn gluten meal per thousand square feet of turf to your lawn this weekend or next. (That's the new legal limit in Maryland and Virginia.) Then do the same thing in mid-August. You'll provide a gentle feeding both times, as well as preventing crabgrass now and chickweed, clover, dandelion and other cool-season weeds in the fall.
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