Dear Master Gardener: What are easy to care for indoor plants that will brighten these dark winter days and nights?

Answer: Green plants and flowers can cheer us up, especially during the long, dark days of winter. Although a popular NASA study claimed that houseplants can remove some air pollutants, newer research shows that because our homes and offices are so different from the lab, you would need close to one plant per square foot to even register any effect! But the psychological benefits of caring for indoor plants still make it a great year around hobby.

Having enough light for your plants, without putting them too close to cold windows, is the biggest challenge. Low humidity can be overcome by running a humidifier or placing pots on pebble-filled trays with a bit of water that will evaporate upwards. Don’t mist your plants. Damp leaves are a perfect breeding ground for bacterial or fungal diseases.

The following houseplants are very easy to grow: Croton, Chinese evergreen, Dracaena, Palm, Peace lily, Pothos, Philodendron, Sansevieria (also known as snake plant or mother-in-law’s tongue), and Spider plant. Christmas cactus, Kalanchoe, African violet, and Orchids are long-lived, flowering plants with long bloom times that can also add a pop of color and cheer to your home.

Dear Master Gardener: I brought a fern in a hanging pot and some begonias and coleus indoors to overwinter and noticed they have whiteflies. How do I get rid of them?

Answer: Whiteflies, which are not flies, are more like scales, mealy bugs, and aphids. The adult whiteflies are tiny (1/16 inch) and the young ones are even smaller. They are pale in color and difficult to see. Whiteflies flutter up when you water or handle a plant they are on. They suck the plant sap with their piercing-sucking mouthparts, which cause infested leaves to yellow and drop, reducing the plant’s health but usually not killing it. These insects are usually more of a problem in greenhouses than homes. Begonia, coleus, and ferns are plants that are susceptible to whiteflies. Washing the leaves, neem oil, or for more serious cases pyrethrum or bifenthrin, may be used to control these pests.

Dear Master Gardener: Is it true that you can grow an avocado tree from an avocado you buy at the grocery store? If so, how do you grow one?

Answer: Yes, it is possible to grow an avocado tree from an avocado purchased at your local grocery store. In addition, it can be a fun horticultural project to do with children. If your purpose in growing an avocado tree is to eat the fruit, you will have a long wait and the taste of the avocado will most likely be different than the parent fruit. An avocado tree planted from seed may take seven to ten years to start bearing fruit.

To turn your grocery store avocado into a houseplant, remove the seed, wash it, and suspend it over a glass or jar filled with water. You can suspend it by inserting three or four toothpicks into the avocado seed, making sure the wider end of the seed is in the water, covered to about one inch, and the pointed half is out of the water. Keep it in a warm place away from sunlight and keep adding water as needed. You may want to change the water every few weeks. The roots and stems should sprout in about two to six weeks. When the stem has grown about seven inches in length, cut it back to about three inches. When you have thick roots and the tree has started growing out of the top of the seed, plant it in an 8-12-inch diameter pot with good quality potting soil, leaving half the seed exposed. Place the avocado tree in a sunny location and water it lightly and frequently, being careful not to overwater it. Overwatering will cause yellow, curled leaves and soft stems. If the soil is too dry the leaves will turn brown, curl up, and eventually fall off. Fertilize your avocado plant about every three months with a standard houseplant fertilizer.

Avocado seeds may also be started in soil by filling a large container with potting soil then planting the seed so the pointed end is about one inch above the soil surface. Make sure to keep the soil moist at all times until the plant is established.

December Gardening Tips

  • Check on your produce, such as potatoes or winter squash, that you are storing. If anything has shriveled, developed soft spots, smells funny, or shows any signs of rotting -- get rid of it. If you have potatoes sprouting, it means they are not being kept cool enough. If they are turning green, they are exposed to too much light.

  • Poinsettias are easy holiday plants to grow, and contrary to popular belief are not poisonous. Make sure the plant is wrapped well when transporting it from the store to your car in cold weather. If it has a foil wrap, cut the bottom off or poke some holes in it so water will drain out of the pot and the plant isn’t standing in water. Poinsettias prefer a bright location away from drafts. Water thoroughly when the soil surface begins to dry, but don’t let the plant completely dry out.

  • Don’t hesitate to buy a fresh Minnesota-grown Christmas tree. They are a renewable crop grown on marginal agricultural land. Balsam fir is the most fragrant. Fraser fir is also fragrant and popular. Norway pine has stiff branches and needles that will hold heavy ornaments, whereas white pine has softer and longer needles.

  • Try to avoid using deicing chemicals on sidewalks and driveways, as it can damage nearby grass and shrubs. Damp sand, spread lightly will form a gritty nonslip surface and can be swept up in the spring.

  • Throughout the winter months, check your houseplants regularly for signs of insects or disease. Some signs of insect problems include fine webbing, discolored foliage, or shiny, sticky patches on leaves. Wipe insects and dust off of leaves (top and bottom) with a clean, damp cloth.

  • Do not fertilize houseplants at this time of year. Because of low light and poor growing conditions, plants need very little nutrients.

  • Let it snow! Snow insulates and protects plants through winter into spring.

University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. All information given in this column is based on university research. To ask a question, call the Master Gardener Help Line at 218-454-GROW (4769) and leave a recorded message. A Master Gardener will return your call.