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Prevent crabgrass the natural way

Friday - 2/18/2011, 8:48am  ET

Meet Mike in Chantilly on Friday, Feb. 25. WTOP Garden Editor Mike McGrath will appear live at the Capital Home and Garden Show at the Dulles Expo Center in Chantilly, Va. on Friday, Feb. 25. He'll help you get your lawn off drugs at 11 a.m., help you grow your best-tasting tomatoes EVER at 2 p.m., and answer your toughest garden questions at 4 p.m. (NOTE: Mike will only be there on Friday.) More info:

Don't pollute -- prevent crabgrass the natural way

Doug down in Port Tobacco writes, "We recently moved to a neighborhood where we'll be getting our water from a well instead of public water. So I don't want to use the 'Scott's with Crabgrass preventer' I have relied on in years past. Is there a natural and effective way to nourish my turf and kill the crabgrass before it gets started?"

Ah, I love it when people finally get religion. Yes Doug, there is a natural weed and feed. (WTOP listeners have been hearing me talk about it every Spring for over a decade.) It's corn gluten meal.

Corn gluten is the perfect high nitrogen lawn food (right around 10 percent - pretty much the highest concentration any natural fertilizer can achieve), and it contains natural compounds that inhibit the germination of weed seeds.

It's widely available under a variety of brand names at larger garden centers (especially the local, independent ones) and via mail-order from Gardens Alive. But timing is crucial with all pre-emergents. It must be applied to your turf just as the local forsythia and redbuds burst into bloom. (Or if you're a techno-geek, when a soil temp thermometer reads 55 degrees.)

When is a lawn worth treating?

Jason in Calvert County writes, "Our front yard was sodded in 2003, but much of the topsoil was first "reallocated" to other homes being built in the area and I fear there wasn't an adequate base of soil for the sod. The yard is now overrun with crabgrass and every other weed imaginable. I'm trying to limit the amount of chemicals I use, as we are close to the Bay and on well water. I've heard you refer to corn gluten meal but don't want to waste more money if this lawn is a lost cause. Is it worth it to apply CGM this Spring?"

Well, Jason, the basic rule here is 50 percent. If a lawn is more than half weeds, the best advice is to just cut it high this summer, then be prepared to tear it up and have a new lawn seeded in a rich bed of compost in late August. (The ideal lawn seeding window in the D.C. area is Aug. 15 - Sept. 15. Spring and summer seedings are a waste of money).

But if it's more than half grass, then do apply corn gluten as a weed and feed this spring. Ten- to 20 pounds per thousand square feet of turf. Then do not cut the lawn below three inches. Do not feed it in the summer. Water it deeply but infrequently when needed and the weeds should be forced out naturally over time by the now-well-cared-for grass.

Protecting lawns from road salt damage

Gary in Olney writes, "HELP! I live on a street that has salt and other chemicals applied quite liberally after the road is plowed. What can I do to reduce the salt damage to my lawn short of erecting an eight-foot high concrete wall?"

Actually, a much smaller engineering project is recommended for folks like you, Gary. This summer, create a small drain-like ditch at the margins of your lawn to carry away most of the salty melting snow. Then as soon as possible after a hard winter, soak the salt out of the lawn edges with a heavy watering. Don't use rock salt to melt ice in the winter, and don't use chemical lawn fertilizers -- they're salt-based and would add saltiness to your saline load.

Turning a dog run into a tomato trove

Kim in Rockville writes, "I want to reclaim a former dog-run. The area gets so much sun, we'd like to use it to grow herbs and tomatoes. But we're wondering what sort of organic clean-up we should do first, and how long we should wait before we plant edibles there."

Very smart, Kim. The danger of you picking up parasites from that soil is high. (That's right -- the risk is to the people who work in the dirt, not to the plants or their fruits.)

You should not walk in that area unless you're wearing sturdy shoes, and you should not touch the soil with bare hands. In fact, posting a small sign that says 'no direct skin contact with soil' would be a great reminder for when spring makes us all busy and distracted.

Avoid bad soil entirely. Build raised beds

In our last thrilling episode, Kim in Rockville wanted to know how to reclaim a sunny dog run and turn it into a bed for tomatoes and herbs. This basic problem is not uncommon in our area. In addition to possible parasites, many of our soils contain way too much lead, especially in urban areas.

That's why I'm always advising people to build raised beds for their summer veggies. The garden will be much more productive, and the potentially iffy soil is out of the picture. (It was probably nasty plant-killing clay anyway.)

Here's how:

  • Wearing gloves, work books, long sleeves and long plants, scrape the surface of the soil clean. (If you suspect lead contamination, wear a dust mask as well.)

  • Then lay single sheets of heavy cardboard over the entire area, and build one foot tall raised beds over top of the cardboard. (Raised beds can be any length you want, but never more than 4 feet wide so that you reach the centers without stepping into the beds. Four feet by 8 feet is the most popular size.) Allow 2 feet in between each bed for your walking lanes.

  • Fill the beds with a mixture of high-quality compost and fresh screened topsoil.

  • Cover the cardboard in your walking lanes with wood chips or shredded bark. (This is the only really safe use for these trashy wood mulches.)

The raised beds will be much more productive than trying to grow in flat, compacted ground. You'll have sealed off any dangerous organisms or elements down below.

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