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Q. Hi Mike: I have two “Pia” hydrangeas planted in clay pots that I would like to keep in their pots. What should I do to winter them over?  I live in a townhouse, don't have a garage, and have very limited garden space in the front of the house. Can I wrap the outer part of the pot 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 has been growing well in an earthenware pot, and is now about 12" high. When is 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-eyed Susan,
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" Question of the Week. Unlike the suburban listener who asked that question, I garden in the middle of the city with most of my herbs in terracotta pots. 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 wondering if the terracotta pots will crack or anything? Thanks!
            ---Kate in Philadelphia

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

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

Second, there is a strong possibility that plants left outside in any kind of pot in areas where the temperature drops below freezing will die. Pots simply don’t provide the kind of protective insulation for those roots that being buried in the soil does. And you ladies can’t use the trick I detailed last week—bringing peppers, impatiens and other tropical plants indoors to provide color in your home over the winter—because the plants named in this week’s questions require a certain number of hours of winter chilling 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 the Spring, these kinds of perennials do best when their roots are tucked into good old garden soil over the winter. (And now through fall is the perfect time to plant!) Just take them out of their pots and put them in the ground anywhere you can find that drains well. If there’s absolutely NO room at your place, ask a friend or relative if you can plant them at their house for the winter. Plant at the same depth they were in their pots, and water them 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 pots can be ‘planted’ right in the ground. This may seem foolish, but it actually provides all the benefits of in-ground insulation without any risk of transplant shock—and it protects the plants’ roots from underground winter gnawing by voles. Just bury the pots, water as directed above and dig them out again in the Spring.

3) Gather all your pots together, place them against the North or east facing 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”. To be safe, I’d remove plants from terra cotta pots and lay the plants down on the ground sideways with as much soil still attached to their roots as possible. (Leave plants inside plastic pots for that little extra vole—and rabbit and mousey—protection.) Dig them out of there as soon as the weather warms up in Spring and put them back out where you want them. You don’t have to wait until after the last frost—they can take a chill, just not a really deep freeze.

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

Oh and that new hydrangea wants to be planted right now (almost EVERYTHING likes to be planted in the Fall!) in full sun to part shade in a very rich soil. So put lots of compost in 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 plant enjoys chemical fertilizers, but hydrangeas like them least of all.

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

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

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