Overwinter Tender Perennials

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Although we live in a relatively warm climate, some of our summer gardens – the “tender perennials” especially, are native to even warmer climates and won’t make it through our frost. Often we consider these beauties as the “summer fling” of our infatuation, and not “true love”. But the appearance of Jack Frost doesn’t have to spell the end of the relationship. By potting them up and overwintering them indoors, you can plant them out next year and fall in love all over again. In making the decision for who makes the cut, beware to choose quality over quantity. Indoor space, transplant effort, and maintenance care can monopolize all your “off-season downtime”. Consider the return on your investment when choosing who gets your attention:  is the plant unusual, expensive, or a sentimental symbol? Then go ahead and take the gamble. Lower light and humidity levels in your indoor winter home make it risky, but outdoor freezes mean all bets are off.

First get ready to downsize. The top growth and roots of your plant will need to be trimmed to help it make the move from an outdoor star to a windowsill lady in waiting. Use some fresh potting mix and a container with good drainage appropriate for the size of the roots. Before bringing a plant indoors, check for pests and diseases. If either are present, treat the plant while it is still outside. Remember, you’re choosing quality and still taking a gamble. Keep the odds in your favor by selecting only healthy plants to overwinter.

Next, understand the obstacles. Whether indoors or outside, plants need light, water and nutrients. The levels of all change when moving to an inside environment. Light will be the most challenging piece of this puzzle. Windows facing south or west allow in enough light to keep most plants going through the winter months. You can supplement low light, especially in December and January, with fluorescent lighting on a timer for about 18 hours a day. If your plant makes it to February, you will likely have a successful springtime re-entry for your garden.

Just as houseplants typically need less water and fertilizer than outdoor plantings, your overwintering experiments do as well. Water only when the soil surface is dry, then water thoroughly. Fertilize sparingly – at the quarter rate of what you would apply outside. Maintenance status is the goal, not pushing new growth.

Low humidity indoors can be as harmful to your plant as insufficient light. Lowering your thermostat will help increase the relative humidity inside and lower your power bill too! Try adding a bit of localized humidity by setting your plants in a tray of water with a layer of gravel to elevate them. If your plants are all kept in a single room, you may want to consider running a humidifier in there.

When the last frost-free date has passed it’s time to take your tender treasures back outside. Here in Sanford, that’s April 19th, give or take 12 days. Be sure to get them acclimatized to the new conditions slowly. Put them outside in a sheltered spot for just an hour or so the first day and gradually increase their exposure to sun and wind each day for about a week. After all, you didn’t cater to them all winter to see them crash and burn in the spring. Don’t be surprised by spindly growth over the winter. Low light levels may have caused your plant to “stretch”. Once they are acclimatized and over the shock of moving to “new digs” again, trim them up nicely, and watch the new growth push through. Love is back in the air again!

Minda Daughtry is Horticulture Agent for North Carolina Cooperative Extension in Lee County.