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Garden Plot: Tomato plants need warm nights

Friday - 5/3/2013, 10:04am  ET

676px-Tomato.jpeg
The days are warm, but for great tomatoes, you need to wait until the cool nights are over. (WTOP file photo)

Tomatoes off to a bad start - if you've already planted them

WTOP's Garden Editor Mike McGrath

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Your last chance to meet Mike in person this spring comes Saturday at Prince William County Compost Awareness Day, at the Balls Ford Road Yard Waste Compost Facility, in Manassas, Va. Mike will present free workshops at 11 a.m. and 1 p.m. and answer all your garden questions. There is more information on the Prince William Trash and Recycling site.

WASHINGTON - We have a region full of planters with itchy fingers. Many of them are asking permission to put their tomato plants in the ground. Many already have. Just remember: It's not the daytime temps that count with tomatoes, peppers and other crops of summer; it's the nighttime lows that can shock the plants and dramatically slow their growth.

Nights in the 40s won't kill your plants as impressively as frost, but it will stunt their growth, and they will resent you for the rest of the summer.

Now, nighttime temps are always warmer in the heat sink of the city, where it's generally OK to jump the gun a bit. But even D.C. temps will drop down into the 40s the next couple of nights. And the nighttime temps in outlying areas are predicted to drop into the low to mid 40s.

So the smart money says to wait. If you already have plants in hand, leave them out during the day, but either bring them back inside at night or at least huddle them up against the side of a building, where the temperature won't drop as much.

If your summer plants are already in the ground, cover them with individual cardboard boxes on really cold nights. If you're going to use spun-polyester row covers, such as Reemay, or sheer curtains to keep them warm, make sure to rig up supports so the covers don't sit directly on the plants.

Don't use plastic, tarps or similar heavy, smothering materials. It's better to take your chances with the cold than to go all cowboy out there.

Remember: This only applies to peppers, eggplant, tomatoes, cukes and such. Cool- weather crops such as lettuce, spinach, peas and broccoli need no protection.

Corn gluten: Too late for crabgrass, not for feeding

John in Laurel is one of many asking the same question: "Is it now too late to apply corn gluten to my fescue lawn to prevent crabgrass?"

Probably, John. The soil temperatures really soared last month, and most of the dormant crabgrass seeds in area lawns have already germinated.

But those lawns still need a spring feeding, and all-natural corn gluten meal has exactly the right amount of slow-release nitrogen to provide the fuel your grass needs to compete against weeds.

Then follow the path of proper lawn care to limit the number of weeds the smart way-by growing a thick, tough lawn:

  • Never cut the grass lower than three inches;
  • Return all clippings to the turf;
  • Water deeply but not frequently; and
  • Don't feed the lawn over the summer; wait until the fall.

You'll be surprised at how big an effect good lawn care can have on weeds.

Grassy weeds around roses: Get cardboard

Rita in Millersville ("just outside of Annapolis") writes: "What's the best way to kill crabgrass in my rose garden?"

I wrote back to say that it seems way too early in the season for new crabgrass to be visually obvious. Rita then confessed that it was last year's dead, brown plants around her roses, and that it actually appears to be Bermuda grass. That makes a lot more sense.

Soak the area thoroughly (this makes weed removal easier) and pull out or dig up as many of the rhizomes as you can. Unlike crabgrass, an annual plant that grows from dropped seed, Bermuda grass is a perennial that will green up again fast when warm weather activates those underground creepers. You'll never get them all out, so don't worry about perfection. Just do your best.

Then lay single pieces of cardboard over the cleared area and cover the cardboard with 2 inches of rich, black compost. The cardboard will smother the grass and the compost will naturally feed the roses and provide protection against plant disease.

Don't use wood or bark as your mulch. You should never use any kind of wood or bark mulch underneath roses. It can actively promote black spot and other rose diseases.

Let sleeping dogs and grass clippings lay

Lang, in Alexandria, has a common but very important question: "Should I leave the clippings on the lawn every time I cut the grass?"

Yes, Lang; for several reasons.

Those clippings are 10 percent nitrogen - the primary food that our lawn grasses crave. Removing the clippings starves the lawn. Returning the clippings to the soil provides a gentle feeding every time you mow.

People who foolishly allow their lawns to be treated with chemical herbicides really must return their clippings to the turf, as modern "improved" herbicides are a danger to all plants other than grass, even if those clippings are turned into compost.

You read that right. If you put treated clippings out for recycling or mix them into your compost pile, the resulting compost can kill plants. Yet another reason to just say no to lawn chemicals.

A true mulching mower is the best way to feed your lawn with clippings when you mow. It pulverizes the clippings into a fine powder. Otherwise, keep your mower blade super-sharp and never cut the lawn lower than 3 inches, and your returned clippings will be virtually invisible. (But nothing works as well or as invisibly as a true mulching mower.)

Compost mulch beats wood three ways

Rich, 'who works at the Pentagon,' writes: "Is there a bagged mulch sold in the Washington area that is more organic, i.e., not wood, that I can use to replace all the wood mulch around my house?"

Well, wood mulch is organic in nature, Rich - at least the stuff that hasn't been dyed the color of a Burger King - but it can stunt plants, invite termites, cause serious nuisance mold problems like the house staining artillery fungus and catch on fire.

In a landmark study conducted at three different universities, black yard-waste compost - like Maryland's LeafGro, which is available both bagged and bulk in our region - prevented weeds just as well as wood mulch, but fed and protected nearby plants instead of stunting their growth and didn't breed any nuisance fungi.

And its rich black color is just as attractive as dyed wood mulch-but, unlike wood, that color won't fade.

My second mulch choice: pine straw or pine fines. Just remember that no mulch should ever touch a plant.

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