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Good time to plant a tree, bad time to trim one

Friday - 9/12/2014, 9:50am  ET

WTOP Garden Editor Mike McGrath says it's a great time to plant a new tree, such as this blue spruce, which can thrive in the D.C. region. (Getty)

Editor's Note: Due to a technical glitch, we are reposting Mike McGrath's Garden Plot from Sept. 13, 2013.

This is a great time to plant a new lawn

Greg in Springfield writes: "My little 10-by-10 townhouse lawn gets full sun but dies every year by the beginning of June. How and when should I do the work of replacing it; and what type of grass should I use?"

This is the perfect time of year to seed a new cool-season lawn, Greg. Just remove any weeds, loosen up the soil, add an inch of compost, level the surface well, sow the new seed, cover it with a dusting of compost and mist it gently every morning. The new grass will be up and growing in five to seven days. (If you've been trying to seed in the spring, that's why your lawns have been dying by summer.)

Bluegrass is the best cool-season grass for full sun areas, and it fills in its own bare spots. Just don't cut it lower than three inches or feed it in the summer or you'll lose another lawn.

However, with an area that small, sod is a very affordable alternative. You could lay cool-season sod now or in the spring. (Although you'll probably find better quality sod in the spring.)

And if you've been caring for the lawn fairly correctly and suspect that the intense heat of summer concentrated on such a small area is the reason for your previous failures, you might want to consider zoysia or Bermuda -- warm season grasses that thrive in D.C.-area summers but go tan and dormant in the colder months. Warm season grasses are always installed in the spring.

This is a great time to plant a new tree…

Jim in Charles County writes: "I want to know if I can plant a blue spruce in the same hole I just took a bad flowering cherry tree out of. It wasn't dead, but the bark was peeling and black, so we decided to put it out of its misery. I've always wanted a 'Christmas tree' in the front yard. Any advice for me?"

Yes, Jim. Blue spruces are slow-growing beautiful specimen trees that typically do very well in the region as long as they receive sun on all sides. (Otherwise the lower branches turn brown.) And this is the perfect time of year to plant new trees. You have a much better rate of survival than with trees planted in spring.

But I'm worried about why the previous tree suffered. If you have your lawn treated with chemical herbicides, I suggest you either go organic with your lawn care or forget about planting any new trees.

Otherwise, remove all wrappings before planting (no matter what anyone else tells you), plant the tree high in the ground, not deep (you want to see the root flare above the soil line), do not improve the soil in the planting hole (fill it back with up with your regular old dirt), mulch with an inch of compost (not wood, bark or root mulch) and let a hose gently drip at the base of the tree for several hours after planting. Repeat this 'drip irrigation' every two or three days if there isn't good rain.

…But this is a terrible time to trim trees!

Trimming trees this way is called pollarding. Aside from being ugly, McGrath says it's not dangerous. What is dangerous is doing it now. (Courtesy of Mike McGrath)

Ed in Fairfax writes: "I live in a condo community. Recently, the board sent out a letter telling us to expect some tree trimming on the property due to fact that some of the trees were growing too high and close to our buildings. I would say they did more than 'trim' the trees and am sending you photos of the aftermath. Does this look like the proper way to prune a tree? The directive from the board to the company that did the trimming was to reduce the height of the trees by about 15 feet. I have to say, I'm not pleased with the appearance of the trees, and I don't know what the effect will be on their health."

Ed's photos show trees with the tops of all their branches cut off, a controversial technique called 'pollarding' that certainly results in a uniquely unattractive appearance.

The big danger to the health of the trees, however, is in the timing. Big trees should only be pruned from mid-winter through spring. Never in summer or fall. This ill-timed pruning is going to trigger a growth spurt that will interfere with the trees going dormant, and make them very vulnerable to winter injury.

The best Ed can do now is to try and make sure that the trees aren't fed, are protected from exposure to lawn chemicals, and that no mulch touches their trunks. (Hoe it away yourself if you have to!)

And make sure the board knows two things:

  • That those trees now look uuuugggglllyyyy!
  • Their timing could not have been worse.

Crazy-looking caterpillars could deliver a sharp sting!

Timi in Columbia, Md., sent a photo of a very interesting looking caterpillar - - bright green with multi-colored spines on its back. She included the message, "Creepy crawlies don't normally freak me out, but what in the world is this very scary looking thing? It had me running for the hills."

Well, you don't have to run when you see a caterpillar with spines or spikes on its body, Tim, but you are wise not to touch them.

A Columbia Md., resident found this caterpillar in the yard and asked McGrath what it was. (Courtesy of Mike McGrath)

Although not commonly known, some caterpillars can deliver a sting from those spines that's as painful as a wasp or a bee sting.

Your caterpillar is definitely a member of what's known as the 'giant silk worm moth' family, and some of the caterpillars in this family are known to sting (but I'm not sure that yours does).

The photo you sent is a little fuzzy, but I'm guessing it's the larval stage of a Cecropia moth (Hyalophora cecropia), one of the largest moths in North America. The adult moth is also quite a sight -- looking something like a lavishly painted Japanese kite.

Here's a great little article with photos of weird caterpillars in general, including some of the most venomous ones (as well as Timi's new friend).

And finally, here's the article that names and shows the two members of the giant silkworm moth family known to have painful stings.

Gnat, gnat go away (fruit flies, too)

Andre in Mitchellville writes: "I have gnats that only appear at dinner time, which is quite annoying when you're trying to eat. One website suggested that moist soil in our house plants was the source of the problem so we changed the soil. A local garden center then recommended systemic granules, which we used on our houseplant soil. The gnats still persist. Where do you think they are coming from? And what do you recommend?"

Well, if they are fungus gnats (annoying little creatures that breed in houseplant soil), you should keep the plants as dry as possible (which is good for the plants in general), water the plants with BTI (a natural fungus gnat preventative that's mostly used to prevent mosquitoes breeding in standing water), and/or cover the surface of the soil with an inch of sand to prevent breeding. (If the adult flies can't get back into the soil to lay their eggs, the cycle is broken.)

But they might be fruit flies, which look pretty much the same to us and often act just the same at dinner time. To get rid of those flying nuisances, remove all fresh fruit from the area for a week (either put it in the fridge or in sealed containers) and leave out small containers of vinegar or red wine. (Fruit flies can't resist them and will drown themselves.)

Either way, your airborne annoyances should soon disappear.

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