Protecting Rosemary, Fruit Trees and Other Plants in Pots
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Q. Mike: I've tried growing Rosemary in my garden without much success. This spring I grew some in a container and it's done BEAUTIFULLY! My question is whether or not to bring it indoors for the winter. We also have two Lavender plants that are new this year. One is planted in the garden; the other in a container. The one in the container is doing much better. Should we bring it in or leave it out? Thanks,
- ---Bob in Aspen Hill, MD
A. Plants in pots should not be left outside in areas with freezing winters. The only exceptions are 'alpine plants' (rated for the coldest growing zones, like USDA's frigid Zone 3) in very large, shatterproof containers in sheltered locations—but they're never the plants that people are asking about.
For instance, while that rosemary might survive in the right conditions and location outdoors with its roots in the ground in the suburbs of DC, it doesn't have a chance outdoors in a container. Potted rosemary would be guaranteed safe to leave outdoors only in areas with very mild winters, like Southern Florida or California. Even with its roots in the ground, it's only going to overwinter successfully for sure in fairly mild climes or in the heat sink of a big city like Philly or DC. (There are rosemary TREES growing in some community gardens in center city Philly that I greatly envy.) Yes, rosemary (with its roots in the ground) will sometimes survive a mild winter outdoors in an iffy region, but the odds are that it will also perish five years out of ten—especially in wet winters.
You remind me that I have some rosemary in a raised bed that I need to pot up soon and begin the epic struggle of trying to keep alive indoors. Yes, struggle. Unfortunately, I am much too far North to ever expect rosemary to make it through my winter outside, and double unfortunately, indoor rosemary is feisty. Overwatering and/or lack of air circulation practically guarantee the arrival of a nasty white mold on the branches. And if you even slightly underwater it in a dry house, it can turn into a Tim Burton fire hazard overnight.
Your best bet to keep it happy indoors is to repot it into a large container filled with half soil-free mix and half compost, put it in your sunniest window, turn it frequently, water whenever the pot seems light, don't let any water sit in a protective saucer under the pot and light a candle to the Blessed Mother or the Italian Saint of your choice.
The lavenders' survival depends on their variety. Hardy lavender (often referred to as 'English lavender') should easily survive a Northeastern winter outdoors with its roots in the soil. But the tender 'Mediterranean' lavenders (which might be labeled French or Spanish) will survive outdoors only in the interior of big cities and from roughly the Carolinas South. Check the plant tags; if you have a hardy species, plant the currently-containered one in the ground ASAP (after amending the soil to improve the drainage; see below). Otherwise, pot them both up like the rosemary, bring them inside and fret daily.
Now, both rosemary and lavender require excellent drainage, and I suspect that our listener's in-ground losses and disappointments have probably been caused by heavily compacted and/or clay soil. Next season (or this season if you're planting instead of bringing inside), improve their planting areas by mixing in some compost and lots of perlite (a natural, mined 'popped' mineral that looks like tiny Styrofoam balls, available in very large bags at bigger, independent garden centers).
In well-draining soil, our listener's plants should thrive in the summer—and maybe even make it through winter outdoors in that close-to-iffy clime if they're also planted in a sheltered location. Some experts feel that the wintertime death of lavender and rosemary in regions right at the dividing line for Mediterranean plants is more often due to soggy soil than winter cold.
Q. I heard a recent call on your show from a woman with potted peach trees, in which you recommended she either plant the trees directly in the ground or plant the pots in the ground to prevent the roots from freezing over winter. I'm in a similar situation, with a few small potted fruit trees that need a cold spell. However, I live on the second floor of a condo and don't have any ground to plant them in. Is there anything else I can do to help my plants survive the winter?
- ---Chris in New Castle, DE
The best tactic would be to find a place where you can dig a couple of holes somewhere outside before the ground freezes hard, drop the pots into the holes and fill the holes back up with soil until the lip of the container is just below the soil line. (Ask friends and relatives if you can 'borrow' a little bit of their yard for the winter.) Then unearth the pots in the Spring and put them back out on the balcony.
Or try letting the trees go dormant in a basement or garage that doesn't freeze but stays colder than 45° F. (Don't cover them with anything, but you can turn them on their sides). Or take them to a friend's house, lay them down against an outside wall that doesn't face South and cover them with a solid foot of very well-shredded leaves; there's a good chance they'll be fine when you dig them out in the Spring.
The only thing you can't do is leave them outside in their pots….