Q: I was given a calla lily plant early in the summer, with beautiful yellow flowers. I potted it in potting mix and set it in a sunny spot. It has formed a lot of new flowers, but they are green, not yellow. Is there something I need to do to get more yellow flowers? Also, I’ve never grown a calla lily before, but I have read that you can keep them inside over the winter and they will survive. Any tips on how to overwinter my plant?

A: It is normal for a calla lily’s “flowers” to start out green and then turn color as they mature. The colored parts are not really flowers — and calla lilies are not really lilies, for that matter. They’re related to jack-in-the-pulpit, and the showy parts are spathes. If you look inside the spathe, you’ll see a little spike covered with tiny flowers.

Newly grown spathes are normally green. But spathes can be green for other reasons, too. Too much nitrogen in the soil can lead to greening. And in the fall, as the plant prepares to go dormant, spathes that were colorful may turn green.

You’re right that you have to bring your calla lily inside if you want it to survive a Minnesota winter. They are native to South Africa and can’t tolerate cold. You can try growing it as a houseplant if you bring it in well before frost and find a sunny spot for it indoors.

The other option is to let it overwinter in a dormant state. Once we’ve had a light frost and the plant has died back, dig it up. Calla lilies (like iris and canna) grow from underground structures called rhizomes. Cut off the dead foliage, leaving a couple of inches, and let the plant dry in a warm place for a week or two. Brush off the dirt. Then, put the rhizomes in a container that allows air to circulate, such as a mesh bag or a cardboard box with holes in it, and store it somewhere cool and dry.

It can be tricky to find a spot in the house that is neither too warm nor too cold; you’re looking for something between 40 and 55 degrees.

In spring, you can plant the rhizomes outdoors, 4-6 inches deep and 18 inches apart, after all danger of frost is past. If you want to grow your calla lily in a pot again, you can plant it indoors six to eight weeks before the last spring frost. Plant it 2-4 inches deep in the pot. Keep it warm and moist. Once foliage appears, place the plant under lights (fluorescent or LED shop lights work well for indoor growing). This plant must be “hardened off” before you can set it where you want it outside.

Put it outdoors in a shaded place for an hour the first day, then gradually increase its exposure to sun and wind over about a week. After it’s toughened up, set it in a sunny spot for the summer.

Written by U of M Extension Master Gardeners in St. Louis County. Send questions to  features@duluthnews.com .