Help for a newbie on overwintering plants?

[Syme]

Just spent my first summer here in northern zone 6 with a beautiful balcony garden. I want to overwinter some plants, but I'm unsure on how to do it. I would *really* appreciate advice on what to do since I've never overwintered.

Some info:
Everything is in containers.
I have several south-ish facing windows that get several hours of sun.
Our apartment balcony is on the 3rd floor. It's covered, surrounded by walls on 3 sides, and set into the building about 4 feet.
I have an unheated utility closet off the balcony that receives no sunlight.

Here is what I want to overwinter:

Hibiscus (tiny little guy, brought him in last night)
Wax begonia (as a few long arms protruding out, not sure if I should trim back or not)
Arp Rosemary
Lavender
Mint
Oregano (currently in one of those mossy hanging baskets with two annual herbs so he'll need repotting)
Snapdragons
Columbine
Strawberry (debating on if this would be worth the trouble or not)
Annual geranium (long shot probably, but I read sometimes they'll overwinter indoors).

If it's not too much trouble, could someone kindly give me advise on where I should put these guys and if they should be covered or not? I have some larger pots with tomatoes in them now that I could use to bury some pots if that's best for them. I really am clueless.

[nedwina]

Overwintering success depends on what kind of plant & how its stored. And very careful watering.

Actually, your geranium will probably be the easiest one. Put it in the sunny window & water only when dry. They prefer cooler temperatures indoors, but in general they do ok so long as they get enough light & don't get soggy. The begonia will probably do ok in the window too. (It's ok to trim- just keep the watering light until it leafs back out some.) If it starts to look wonky, move it to indirect light and see if that helps. Since the hibiscus is just a sprout, put it in the sunny window too.

Your woody tender perennials, like the rosemary & lavender, would do better to be let go dormant in a cool darkish location, rather than keeping them awake under lights in a warm room. Same with the mint & columbine. And the strawberry & oregano. (And the hibiscus once it gets bigger.) That utility closet might be ok, so long as it doesn't go below 40 degrees and isn't too drafty. Rosemarys indoors can be bug magnets, and especially won't take overwatering well. (But a dry rosemary is a dead one-so you have to be vigilant!)

You could try leaving most of those just out on the balcony, (with the exception of the rosemary- it won't make it) but that closet would be a better bet because you would control their watering better and it won't be as cold & windy. If you don't have enough room, make decisions on who goes in or out based on zone. You can wrap the pots of the "outsiders" with bubble wrap as a bit of insurance too. And top off the pots with more potting soil or mulch.

A general rule of thumb is to drop a hardiness zone or two when the perennial plant is in a pot. If your plant is hardy to zone 4, keeping it outside in a pot for a zone 6 winter will probably be successful. But if your plant is hardy to zone 6, you should try to create zone 8 conditions/temperatures. Etc., etc. The trouble too, with overwintering in pots, is making sure that they don't get too little or too much water (or snow melt) or wind abuse. Some professional growers assemble white plastic hoop houses over their stock- or people like me strip them of their leaves & stash them in the cold garage and water lightly until spring.

The snaps are a tough call. Even though they're considered annuals, some kinds will survive a winter in the ground & come back in the spring with the right microclimate...so you can keep it with the other perennials, or put it in the window with the annuals & see what happens.

Mints in general don't do well in pots over time. So if the mint dies, it's probably not you.

When I have a new plant I want to overwinter, I research what it is, (annual/perennial) what zone it's happiest in, country of origin (cool, dry winters? ) and try to replicate it's "normal" conditions as best I can. If they're evergreen I leave them alone, if they usually drop their leaves, I strip them or wait till they drop them on their own & then store. I overwinter alot of plants in my unheated garage- you get a feel for who's a good candidate & who's not, and what they need to make it after awhile.

If you do put them in the closet, check them more often as spring nears- you'll see bud growth and signs of awakening in late March/early April. Then you'll start the hardening off dance- put them out for a bit by day & back in at night. (Or even just open & close the door.) Once temps are consistently in the 40s, you can take them out & leave them.

Hope this helps. (And I didn't cover everything, but I'll give ya a break & stop here, LOL.) Good luck & welcome to the wonderful world of overwintering! A great hobby for the cheap & ambitious.

[rainbowgardener]

Yeah, I would think the lavender, mint, oregano could stay out on the balcony. Maybe get a bale of straw and pack it around the pots to protect it a bit from freeze thaw cycles and they should be fine. I have them in ground all winter here in zone 6b and they do fine, but as nedwina noted, containers are tougher than in ground, hence the straw bale.

"Annual geranium" is actually pelargonium, a tender perennial. I have had mixed results with it. Some years I have brought them in and they have done great and bloomed and bloomed all winter. Some years they have struggled and barely survived. I don't know what the difference is. A lot of people just take cuttings off their geraniums, root the cuttings and grow those out for new plants for the following year.

[nedwina]

Speaking of freeze/thaw, I was assuming there that the pots were plastic. Which in general are better for overwintering- better insulation and very low odds of cracking with the freeze/thaw cycles. If they are terra cotta & left on the balcony, be very careful with watering, definitley insulate them somehow, and be mindful that if they're loaded with water they're super vulnerable to cracking if the temps drop & the water expands. Those thick glazed Vietnamese pots are pretty resistant, but all others are too thin & porous.

People try all kinds of crazy stuff with geraniums- the "yank 'em from their pots, shake and hang upside down in the basement or attic" thing is a huge mystery to me. I wonder if it worked once & became some kind of urban myth. And there are quite a few variations of that method. Granted, they're tougher than they look, and cuttings last a remarkably long time as they're curing, but since they lack any kind of life saving tuber, the whole soiless storage thang seems highly unlikely to me. (Or only works in the narrowest of conditions. Disclaimer: I have never tried it.)

I used to root prune & repot into a smaller pot. Which was often successful. But I suspect that's just another way to ensure minimal watering & quick drying of the soil.

[Kisal]

I used to overwinter geraniums (pelargonium) all the time. The best success I had was taking cuttings about 5 or 6 inches long from the plants, allowing the cut ends to air dry out of direct sunlight, then potting them up in a well-draining potting mix. I kept them in a cool (unheated) room in a south window, where they received bright light, with a couple hours of direct sun.

Whenever I tried to overwinter entire plants, rather than cuttings, they would be leggy and rangy looking the second year. The cuttings, however, produced nice compact plants that flowered constantly.