Overwintering perennials

(Question)

Please advise if and when should I be moving the following potted plants to the garage over the winter:

1) Hosta.

2) Hens & Chicks.

3) Perennial Dwarf Sweet William.

Thanks.

(Answer)

You don’t tell us where you live but the 3 plants that you are concerned about are hardy in zones 2-9. Plants that you are planning to leave in pots should be rated two zones colder than your area. For example in Toronto we are in zone 6, so you can successfully overwinter plants in containers that are rated zones 1 through to 4. This is because the roots of the plants will experience more extremes in temperature than those grown in the soil. Pots should be move to an unheated garage or shed in late fall when they are dormant and we have experienced several frosts. They should be given a thorough watering before you leave them for the winter and you should check them periodically to make sure that they haven’t dried out. If the pots are very large they can be left in place because the larger soil volume will help to insulate the roots and keep the soil temperature more even.  Do however keep in mind that if the containers are a dark plastic and they are in the sun, they will absorb heat and you might have a problem with freezing and thawing of the roots which might kill them.  You should also be aware that the pots should be plastic as clay, ceramic or cement pots may crack during any freeze/thaw cycles. In the spring you can slowly bring the plants back out into the light and replace them in their positions.