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Protecting Potted Plants over Winter

Q. Hi Mike: I have two "Pia" hydrangeas planted in clay potsthat I would like to keep in their pots. What should I do to winter themover?  I live in a townhouse, don't have a garage, and have very limitedgarden space in the front of the house. Can I wrap the outer part of thepot to keep it from freezing and just keep the pots in front of the house? And would I need to water them or just let them go completely dormant? Thanks in advance,
           ---Isabel; near Washington, DC

Mike: a friend gave me a hydrangea clipping from her garden. It hasbeen growing well in an earthenware pot, and is now about 12" high. Whenis a safe time to plant it? What, if any, soil preparation do you recommend?What kind of fertilizer do I use? Thanks!
           ---Louise; Pottstown, PA

What is the best place to over-winter perennials in pots? I have Black-eyedSusan,
iris, lily of the valley, lambs ears, bee balm, etc.  Thanks
           ---Audrey, Bethlehem PA

Hi: I enjoyed your recent "will my herbs survive the winter" Questionof the Week. Unlike the suburban listener who asked that question,I garden in the middle of the city with most of my herbs in terracottapots. What do I have to do to keep them safe through the winter? They are not fancy varieties, and may be fairly hardy—but I was wonderingif the terracotta pots will crack or anything? Thanks!
           ---Kate in Philadelphia

A. Excellent timing ladies! Thanks to youse, we're going to savea lot of plants—and pots—this winter.

First, it is EXTREMELY likely that pots made of terra cotta, clay orany other heavy, stone-like material will indeed shatter if left outsideover winter. When the soil inside freezes and thaws, it cracks the poorpots wide open. I've even lost EMPTY pots left outside during really severewinters.  So lesson #1: Don't leave stoneware containers outside overwinter if you're gonna get all whiney when they break.

Second, there is a strong possibility that plants left outside in anykind of pot in areas where the temperature drops below freezing will die.Pots simply don't provide the kind of protective insulation for those rootsthat being buried in the soil does. And you ladies can't use the trickI detailed last week—bringing peppers, impatiens and other tropical plantsindoors to provide color in your home over the winter—because the plantsnamed in this week's questions require a certain number of hours of winterchilling to flower correctly, OK?

Now—here are your four basic potted perennial plant options for winter.

1) Plant the plants. Even if you intend to dig them up again in theSpring, these kinds of perennials do best when their roots are tucked intogood old garden soil over the winter. (And now through fall is the perfecttime to plant!) Just take them out of their pots and put them in the groundanywhere you can find that drains well. If there's absolutely NO room atyour place, ask a friend or relative if you can plant them at their housefor the winter. Plant at the same depth they were in their pots, and waterthem well. Water once a week from now till frost if we don't get any rain,and again if we go a month or more without moisture over winter.

2) Plant the pots. Again, not if they're terra cotta. But plastic potscan be 'planted' right in the ground. This may seem foolish, but it actuallyprovides all the benefits of in-ground insulation without any risk of transplantshock—and it protects the plants' roots from underground winter gnawingby voles. Just bury the pots, water as directed above and dig them outagain in the Spring.

3) Gather all your pots together, place them against the North or eastfacing side of your home and cover them a good foot deep in shredded (NOT'whole'!) leaves after the trees give up their previous "Fall Gold". Tobe safe, I'd remove plants from terra cotta pots and lay the plants downon the ground sideways with as much soil still attached to their rootsas possible. (Leave plants inside plastic pots for that little extra vole—andrabbit and mousey—protection.) Dig them out of there as soon as the weatherwarms up in Spring and put them back out where you want them. You don'thave to wait until after the last frost—they can take a chill, just nota really deep freeze.

4) Take the pots into a cool, dark place that will remain between 40and 50 degrees and allow them to go dormant. Water them once when you putthem down and then leave them alone till Spring, when you will take themback outside as soon as the weather warms. Water them well right away,and until we get rain.

Oh and that new hydrangeawants to be planted right now (almost EVERYTHING likes to be planted inthe Fall!) in full sun to part shade in a very rich soil. So put lots ofcompostin the hole—which is also the plant food part of the equation: Compost!A whole bunch now and then a fresh inch a year on top of the soil. No plantenjoys chemical fertilizers, but hydrangeas like them least of all.

So do NOT use chemical fertilizers! I will know if you do, and I willsend Robby the Organic Robot after you.

You Bet Your Garden   Question of the Week  ©2005Mike McGrath

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