How cold do perennials need to get before going dormant?

I haven't been able to find this info out.

For overwintering perennials, I understand that they can't be kept indoors because they need to get cold, go into dormancy and revive in the spring. But getting too cold outside will kill them.

I've seen hardiness zones for my flowers, platycodon and aquilegia being 3b. But what is the highest temperature they need to go dormant?

If it's 15C, I could put them in pots and use the basement for winter. If it's below freezing, I'd do my balcony with insulation. It's tricky since I live in an apartment in zone 5.

Hi Blake. Actually not all perennials need to go dormant....some do because they need a rest period, and others because it gets cold and what is above ground freezes. Some plants stay green even when exposed to below freezing temperatures. The hardiness zone just tells you how low a temperature a plant can withstand before it dies/freezes.

Usually plants that enjoy winter dormancy start dying back around the time of the first heavy frost. Hours of daylight also trigger dormancy in some plants. and dying back is how the plant stays in check. Some plants only bloom on new growth. Typically it is fruit trees that require so many "chill hours" in order to produce fruit in the spring.

If i remember correctly. zone 3 has a minimum temperature of 30 to 40 degrees below 0Farenheit. You are in zone 5a which I think is listed as 0 to -10F. Therefore, you should be able to leave your containers out until the frost causes them to start dying back, and then move them into the basement for the winter.. You will still need to water them periodically and can bring them back out to the balcony when the temperatures rise above freezing.

I hope that helps.

Thanks,

I'm just worried the basement won't be cold enough for them. I think the columbines especially would need the rest period because their germination requires a cold period, and it must be how the plant has evolved.

I have been thinking about this, the rule of thumb seems to be that when you grow a plant in a container, you "lose" a zone or two of hardiness in the winter. Since your plants are hardy to zone 3 and you are in zone 5, they should be alright on the balcony with some protection.You mentioned "insulating" your balcony...perhaps the pots could be placed in a box filled with packing peanuts and then covered for the very coldest nights...you would have the benefit of having them easily accessible to give them occasional water and not have to worry about the chill factor.

Here is a bit more info

http://www.perennialresource.com/articles/181_The-Complete-Guide-to-Growing-Perennials-in-Containers.aspx





Here is some additional info...

http://www.perennialresource.com/articles/181_The-Complete-Guide-to-Growing-Perennials-in-Containers.aspx

Yeah, I have an old blanket I could use to insulate and throw it out when I'm done, maybe fitting it inside a box. I figure if it's pressed up against the balcony door, it'll get some ambient heat since the radiator's nearby, and my balcony is concave, so it won't get as much wind chill.. Otherwise, I could use our building's storage room, which is unheated and has a broken window (silver lining). I guess I'll have to measure the temperature there when it gets cold, but it's good to know I can use containers since I have a couple of options.

Thanks for the info and for the additional info. :)

You are very welcome Blake...it is always good to have options...GRIN