What to do with perennials planted in pots over the winter
Hello, I have several perennials planted in pots as I live in a townhome and am prohibited from planting in the ground. Can I leave them in the pots over the winter? If not, how do I winterize them for re-planting in the spring? Thank you
Hennepin County Minnesota
Thanks for your question. In general, perennials in pots will survive the winter in Minnesota. But it would be helpful for us to know exactly which perennials. Winterizing typically includes putting them in a larger pot, with soil or packing material between the 2 pots. Perennials do not need to be brought inside; they're used to or in need of the cold of winter.
Thank you for your advise and timely response. The perennials I have in pots are Day Lilies, Black Eyed Susan, Lavender and Shasta Daises. I appreciate you time.
Eden Prairie MN
Great! Day lilies are able to survive as perennials due to their underground structure. Lavender is a woody perennial, and you might want to trim it back by a third to keep it bushing out. Shasta daisies are pretty hardy perennials. Some Black eyed Susans are perennial and others annuals in your climate, but if they have survived prior winters, you probably have a perennial variety.
The major risk you have for each of these is that (1) the soil dries out around the roots over the winter and (2) the air is much colder above ground than under, and winds will dry out the container and freeze the roots. So, packing them in cardboard boxes surrounded by packing peanuts or a dense compost will help protect the pots, and an occasional watering (unless they're rained and/or snowed on) will protect the roots. Before winter arrives, all potted plants should have a good watering, again for the sake of the roots. Adding a mulch to the soil at the top of the pot(s) will help all but the lavender, which by its woody structure takes care of itself.
Hope this is helpful. Good luck!
I am very appreciative of your time and willingness to answer my questions. Thank you once again.
You're most welcome!
Let me add a little to the response you received. You are in zone 4b, which means you can get -25 degree winter temps. Although most of your plants can handle that if they were in the ground, they will die if their roots are not significantly protected from the cold weather. Since you cannot supply the preferred insulation from surrounding earth, you need to replicate it.
If you have the option of moving them into an area (like a heated garage or a basement) that does not freeze, the plants should do fine. Once they die back naturally from our cold weather, cut them back to just above the soil and water them well. Check them occasionally while in storage and water them to keep the soil from totally drying out. If it is cold enough they should stay dormant and not need much water.
If this is not possible you need to supply lots of protection. After the plants are cut back and watered, put the pots on the ground if possible and surround them with a foot or more of insulating material. More is much better in this case. Some people make a fence of lightweight fencing (like chicken wire) and fill with leaves or straw. Bags of leaves also work well and are easier to remove in the spring. Snow is a good insulator, so piling that on top is useful. However, don't count on snow as we often have damagingly cold temps before we have significant snow.
Make sure to have protection on all sides of the pots or group of pots. If they are on the ground (dirt or grass) they don't need anything below them. The earth will actually provide heat. The plant soil will freeze even with the insulation, so there is no need to water during the winter. However, your pots can crack.
Lavender in the ground is only reliably hardy in zones 5 or warmer, depending on the kind of lavender you have. It requires extra insulation (maybe put it in the center of the group of containers) or should be moved indoors and treated as a houseplant. It needs a sunny window and probably will look a little ragged by spring. You can do the same with your other plants if you want. The daylily has a vigorous root system, so check to make sure it does not need a bigger pot.
Because of the special care our containerized perennials need, many people who can ot permanently or temporarily plant them in the ground find it easier to replace their plants each spring. Even heavily mulched the plants may not survive, especially if we have a harsh winter.
I know how frustrating it is to overwinter containers. Just remember that just because something is listed as hardy in your zone does not mean it is hardy in a container in your zone. Even something shown as hardy in zone 2 (-50 degrees) cannot be grown unprotected in a pot in your zone 4. Root protection is crucial!
Thank you, Terri for your thorough explanations. This winter will be the first in many, many years of gardening that I have planted perennials in pots and truly did not know how to 'winter' them. The protocol of wintering them makes perfect sense but I have made the decision to gift one of my daughters, who has recently purchase her first home with the plants. I am disabled and am not able to protect the plants properly as suggested. This way, the plants win, my daughter wins as do I knowing that the plants will have a greater than good chance of survival and I can enjoy them when I visit her and my grandchildren! I enjoy the opportunity this web site and its information tremendously. Thank you.
That is a fabulous resolution. Make sure she waters the plants well until the ground freezes. Under-watering newly planted things is a major cause of winter kill. Once the ground has frozen, have her cover with 4 or 5 inches of mulch. She may not need to mulch anything other than the lavender in future years, but because she will be planting these so late this season the mulching will help. In another year or two the plants should be big enough that she can dig out a section of them every spring for your pots.
Thanks for using our web site. I also think it is pretty fabulous!