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Baby, it's cold outside -- for plants, too!

Friday - 10/28/2011, 12:11pm  ET

AP: 60a29f05-6e45-419e-9d72-7f7e8a903074
Roots trapped above ground in the winter can freeze, causing the plant to die. (AP Photo/Dean Fosdick)

Are your plants ready for an early taste of winter?

WTOP Garden Editor Mike McGrath

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Don't leave plants in pots outdoors over winter

Bob in Aspen Hill writes: "I've tried growing rosemary in my garden without much success. This spring I put one in a container and it's done BEAUTIFULLY! My question is whether or not to bring it indoors for the winter."

Well, you can't leave rosemary -- or pretty much any plant -- outside in a container over winter, Bob. The roots, trapped above ground, would freeze and the plant would die. (And nine times out of 10, the container will crack as well.)

And rosemary is even tricky in the garden! Our region is right at the dividing line for Mediterranean plants like rosemary being able to survive winter outdoors with their roots in the ground. (In the heat sink of the city, it does fine. Out in the open in the suburbs, it's a crapshoot.)

If you want to risk the outdoors, plant it in your best draining, most sheltered location (not in a low, wet spot out in the open!). Otherwise, bring it inside to your sunniest window, turn it frequently, don't feed it, don't let it get bone dry or overwater it -- and it might survive until spring.

Wise watering over winter -- repot it into a bigger container, using only soil-free mix and compost (no garden dirt). Feel the weight of the pot. Take the pot to a sink, fill the sink with a couple inches of water and let the drainage holes suck the water up for an hour. Now feel the weight again -- it should feel much heavier. Put the plant back in place and "rock" it frequently. Don't water again until it feels light, and never let water sit in the protective saucer underneath.

The lavender hill mob

In our last thrilling episode, we warned Bob in Aspen Hill not to leave rosemary -- or pretty much any plant -- outdoors over winter in a container. "But we also have two lavender plants that are new this year," he adds. "One is in the ground, the other in a container. What should we do with them?"

Well, that depends on the type of lavender, Bob. English lavender should survive winter outdoors in our area with its roots in the ground. If that's what the plant tag says you have, plant both specimens outside in a sheltered location with good drainage.

But Spanish and French lavenders are NOT reliably hardy in our area. Maybe they'll survive inside a walled garden in the heat sink of the District proper (with great draining soil), but not in an exposed area in the burbs with soil that drains poorly.

If you have a tender type, pot them up and bring them indoors to a nice sunny window. Don't feed them. Don't under- or overwater them (see rosemary, above) and think good thoughts -- they're tricky plants indoors.

Making your bed for winter

Jennifer up in Baltimore writes: "I have two raised beds in a local community garden and would like your advice on how to best winterize and prepare these plots for the upcoming spring. So far I've only concentrated on weeding. I typically add some compost to the soil, and mulch with an inch or two of Leafgro in the spring. But what should I do this fall?"

Continue weeding the beds, Jenn -- and then cover them with an inch or two of well-shredded leaves to maintain their soil nutrients and prevent heaving and thawing. Push the shredded leaves to the side in the spring, add your compost and Leafgro to the surface of the soil -- don't mix them in, tilling causes weed problems -- and then re-use the shredded leaves as a weed-suppressing mulch.

Sure, you can still sod!

Brian in D.C. writes: "The city has been working on our road for the last few months, and this has taken a heavy toll on a relatively small area of our lawn; the grass has pretty much been destroyed. I was going to have sod laid over the area but now I'm wondering if it's gotten too late in the year."

Not at all, Brian! Although sod is much more expensive than seed, it has the distinct advantage of having much longer and more frequent windows of application. Unlike grass seed, you can install sod in the spring or the fall. And in the fall, all it needs is about four to six weeks before the soil freezes hard to get established. So if you can still get the sod you want, go right ahead -- you'd have to wait almost a year to sow new seed.

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