Keeping houseplants healthy during winter

Here’s my No. 1 tip for dealing with fungus gnats: Since the larvae love moisture and live in the top 1/2 inch of your soil, the best thing you can do is allow the soil to dry out between waterings.

Here are eight more things you can do:

1. Set up yellow sticky traps (the color of the image included with this column). Stand them up vertically ON the soil and lean it against the stem.

2. Double-check and quarantine any new plants you bring inside.

3. Water your plants from the bottom.

4. Fill a wide-brimmed container with apple cider vinegar, cider or cheap beer.

5. Dice a raw potato into cubes and bury them halfway into the soil. The next day, lift them out and check for larvae which are clear or translucent, about 5 mm long with a black head.

6. Brew a batch of strong chamomile tea. Let it cool and mix with 4 parts water. Use to water plants as usual.

7. Sprinkle cinnamon (a known fungicide) — repeat for three weeks.

8. Before you set out to kill the buggers, give them a 24-hour notice. Let them know your intention. Sounds crazy, but it works!

Fungus gnats are just one of the challenges of keeping indoor plants happy and healthy. After all, you’re in charge of controlling many crucial environmental factors such as light, temperature, humidity, water and nutrition. The right combination results in healthy plants. Too much or too little of any factor results in poor plant health or death. And winter can bring many factors into play at one time.

Speaking of winter, a friend of mine visited Bell’s Nursery in Anchorage in search of a houseplant that could survive on her kitchen windowsill.

“Winter is rough on plants,” a staff person told her. “It’s unfair to expect them to remain lively during the indoor season that lasts twice as long as the outdoor one.”

Perhaps the major environmental factor limiting plant growth indoors is lack of adequate light. Light is especially important in Alaska winters when the hours of natural light are at a minimum. Plants will tell you if they suffer from lack of light: Stems grow abnormally long, their leaves lack color, or they are dwarfed and eventually fall off.

The easiest way to adjust light intensity is to move the plant closer to or farther from a light source such as a window. Unfortunately, this may place the plant in an inconvenient or too cold of a spot. Alternative ways to increase light intensity include:

• Moving the plant to a lighter room (southern versus northern exposure)

• Providing separate artificial (fluorescent or LED) light for the plant. (Set up a timer to turn them on and off automatically.)

• Providing reflected light with a light-colored wall or mirror.

• Keeping leaves free of dust and grime.

It goes without saying that plants also need water. Water is the most important, and often abused, cultural practice. Too much water — no matter the season — can cause lower leaves to curl and wilt; stems can become mushy, soft and rot.

On the other hand, if a plant is water-starved, tips of leaves turn brown and wilt; leaves turn yellow and fall.

Either way, the soil must contain moisture as well as air pockets. If the soil is too wet there is no room left for air. Use a good potting soil and make sure there is at least one hole in the bottom of the container to allow excess water to drain away. Has it been 10 years since you repotted your houseplants?

The following tips may help you develop a watering plan for your plants:

• Use a good quality potting soil. Add a handful or two of compost.

• Make sure containers have at least one drainage hole.

• When watering, apply enough water to run out the drainage hole. (This helps reduce the buildup of white, crusty salts, by the way.) If the soil has pulled away from the inside edges of the pot, causing the water to flush out the bottom too quickly, scratch the soil back in place using a dinner fork.

• Do not allow pots to sit in excess water. Pour it off or raise pots on pebbles.

While we grow houseplants for any number of reasons, I think we really appreciate them during the winter. Facebook abounds with images of pink, red, and orange Christmas cactus blossoms.

Plants not only lift our spirits during the dark days, they clean the air indoors. All plants absorb carbon dioxide and release oxygen, but indoor plants can also eliminate significant amounts of airborne toxins. 

You might recall NASA’s Clean Air Studies in the late 1980s. They showed that certain common indoor plants removed toxins such as benzene, formaldehyde and trichloroethylene from the air. Many of these toxins are present in household products, glues, permanent press fabrics, carpets, upholstery, paper product coatings, pressboard and plywood. It’s a hefty list, I’m afraid.

So which plants are best? According to NASA, a dozen house plants growing in containers that measure 6 to 8 inches in diameter can really improve the air you breathe. The Rule of thumb is one plant per 100 square feet of space. 

Fortunately, NASA’s list of recommended plants contains many easy-to-grow plants.

The peace lily, Spathiphyllum, is indestructible and easy to maintain. Thus, if you want cleaner air but feel you suffer from BTS (Black Thumb Syndrome) then try peace lilies.

Also easy to grow is the Boston fern, the top remover of formaldehyde from the air. The spider plant (Chlorophytum comosum) is another hero, so is the so-called mother-in-law tongue (Sansevieria trifasciata), also known as the snake plant. The heart-leaf philodendron also gets high marks. In fact, lots of philodendrons were studied and were shown to be useful, particularly for clearing out formaldehyde.

Of course NASA’s studies involved healthy, vibrant plants, as in ones that are photosynthesizing to their heart’s content.

In the winter, though, if you wish to enjoy your houseplants and the many benefits they bring, then give them the care and attention they need. It only requires a few minutes of your time. And go about it thoughtfully, with intention.

At the very least, provide some supplemental light. As we approach the shortest day of the year, what could be better than a little more light in your life?

Learn about organic gardening, discover recipes, and go on garden tours on my Gardener’s Coach YouTube channel: https://www.youtube.com/TheGardenersCoach. Have a gardening question? marion@gardenerscoach.com