When the mums come out we know it's time for the houseplants to come inside.

If you let your houseplants "vacation" on the back deck or front porch this summer, then it's time to get them ready to come inside and purify the air, which helps get us through the long Midwest winter.

But take heed, you can't just carry those plants in without giving them a thorough inspection and cleaning. Not only can the plants have bugs on them but the dirt may harbor little visitors as well.

Nikki Witkowski, Purdue Extension Lake County horticultural educator, and Lyndsay Ploehn, Purdue Extension Porter County agriculture and natural resources extension associate, share some simple steps to help make the transition smooth.

Clean them up

"Give your plants a good cleaning by removing any dead or damaged leaves, or spent flowers. Then make sure they are well watered to flush out insects," Witkowski said.

Inspect the plants for hitchhikers.

"Make sure to spray under the leaves as well as on top because that is where bugs will hide," Ploehn said.

Witkowski does not recommend using soap or insecticide because it can harm helpful bacteria in the soil but she does recommend careful inspection of the leaves and stems and submerging smaller plants in water for 15 minutes to send insects scrambling for higher ground. This shouldn't be done with plants that go semi-dormant or dormant in the winter (e.g. succulents, bulbous plants), as these plants need dry soil throughout their dormant period.

Make sure you scrub the pots thoroughly before bringing them in. Spiders like dark moist places on the bottoms of pots to leave their eggs to hatch.

They recommend that you don't leave the plants out after cleaning them but, if possible, moving them to a garage to dry overnight before bringing indoors.

If the plants have been in full sun they suggest moving them to a shady area for a few days before taking them in. This will help to eliminate the low light stress that causes leaves to yellow and fall off.

"People often mistake this (yellowing of leaves) thinking the plant needs more water," Witkowski said. "The result is they over water the plant and can kill it."

If the plant has grown over the summer, you may want to consider either pruning or repotting the houseplant. If you are pruning it back, do not prune back more than 1/3 of the plant. Witkowski recommends 1/4 to 1/8 only and said if you don't want the plant to get any larger treat it like a bonsai and trim the roots to fit the pot it is in.

If you will be repotting, move it to a container that is at least 2 inches larger than the container the houseplant is currently in.

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Avoid heat registers

"Don't put the plants near heat registers," Ploehn said. "There are no plants that will survive being near a heat source during the winter."

Increase humidity

Humidity levels tend to be much lower indoors than outdoors. This is especially true once furnaces kick in. Running a room humidifier by your plants is one way to solve the problem. But there are other solutions which take far less electricity.

"If you have the space to group a lot of houseplants together they transpire together for  extra moisture," Witkowski said. "The other solution is a pebble tray in which you can use almost any tray filled with rocks and water and set the plants on top of the rocks or in the case of larger plants simply mist with a spray bottle with water."

Transpiration is the term used to describe the transport of water through an actual, vegetated plant into the atmosphere. 

"Make sure you have your plants near a good light source," Ploehn said. "South or west are best and east if it's all you have but avoid north if at all possible."

Watch your watering

Over watering is the fastest way to kill a houseplant. Outdoor potted plants may have required frequent (even daily) watering during sunny, breezy days. Now that they are back indoors, they don't need as much water -- especially during rainy or cloudy fall weather as they won't get enough light to dry out. Always let the surface of the soil get dry to the touch between watering.

"For the best results with plants use distilled or rain water to water the plants," Ploehn said. "Tap water can have different elements that can actually harm plants, especially if you have a water softener."

Because conditions differ widely between the inside and outside your home, a gradual reintroduction to the indoors is best. Sudden changes in temperature, light and humidity can be traumatic to plants, resulting in yellowed leaves, wilting, and even death.

Last but not least, some of the annuals we buy every year can be overwintered indoors.

"Plants like scented geraniums, coleus, begonias and impatiens often do well as houseplants if you have the room and light for them," Ploehn said. "They probably won't bloom for you but they will keep green until spring."


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