Houseplant Tune-up and Maintenance

Winter can be tough on houseplants.  Many houseplants are sensitive to the length of the natural light they get and become dormant or go into a resting phase during the winter months.  They are exposed to lower humidity and can be subjected to a wider daily range of temperatures than during the summer, especially if they are located in front of a heating vent or radiator or set too close to the surface of a window.

Home heating systems can produce very dry air during the coldest winter months. They take moisture out of the air, often making the humidity level less than twenty percent. This dry air not only makes us feel uncomfortable, but also is not good for most houseplants,  pianos, or computers.  Most plants, with the exception of cacti and succulents, do not like such dry conditions.  The majority of houseplants grow best at 40-60% humidity, but can tolerate levels as low as 20%.

You may want to consider increasing the humidity around your plants. The easiest way is with a cool-vapor humidifier that can increase humidity levels by 25-30%. Another option is to grow plants in a waterproof tray with an inch or so of pebbles, crushed rock, or sand.  Water up to, but not above the level of stony material and make sure the pots do not sit in water or your plants risk getting root rot. Misting to increase humidity provides only a temporary benefit as well as possibly damaging the surrounding area.

Because of houseplants’ winter dormancy, you need to adjust your watering and fertilizing schedules.  Watering at most weekly and sometimes only every other week is usually sufficient.  Use room-temperature water which has not gone through a water softener, and water thoroughly so all the soil is wet. For succulents and cacti, water only to prevent the plants from shriveling up.  Plants need fertilizer only when they are actively growing so fertilizing in winter is generally not recommended for most plants. Repotting should be delayed till a plant starts back into its growing season – usually early spring.  Plants receive less light in the winter so don’t compound this by allowing your plant’s leaves to get too dusty.  A gentle wipe with a damp cloth will help.  Remember plants not only absorb energy from sunlight through their leaves, they also breathe through them.

If you got some new houseplants at Christmas they may have come wrapped with foil  around the pot.  If so, you should remove the foil or punch holes in the bottom to allow drainage.  Excess soil moisture can cause root rot. The following are some specific recommendations for poinsettias and Christmas cactus.

Poinsettias love a lot of light so find them a bright and sunny location.  Without bright light, the colorful red bracts and green leaves will lose their luster and dry out.  In a good location they’ll retain their color for months. One thing poinsettias do not like is drafts.  Keep them away from radiators, air registers, fans, open windows and doorways, and don’t let any part of the plant touch a cold window.  If possible, place your poinsettia in a cooler room at night to extend the blooming time.  A nighttime temperature of around 60 degrees is ideal.  This is to the advantage of the energy concious grower who uses a set-back thermostat in the house.

Examine the soil of your poinsettia regularly and water only when it feels dry.  Always water just enough to soak the soil to the bottom of the pot but don’t let water stand on the surface of the potting soil.

The Christmas cactus is a tough old bird that often thrives more on neglect than on care. They are, however,  prone to flower bud drop, which can be caused by several things.  Correct watering is especially important. Make sure you water properly, especially during blooming.  From fall to spring, you should allow the soil to go dry before watering.  From spring through summer, keep the soil evenly moist.  Letting the soil dry out too much or over watering can both cause buds to drop.

Drafts, both warm and cold, can also cause bud drop, and even slight environmental changes can make buds fall.  Don’t move your Christmas cactus to another location if it has buds or open flowers.  Give it lots of direct light during winter (but not directly in the sun in front of a window).  Give it indirect light during summer.  Too much direct light can hurt this plant.  We place our Christmas cactus outdoors in a partially shaded spot for the summer.

A good source of information about houseplants on the Internet can be found at the University of  Wisconsin’s Horticultural link page at www.uwex.edu/ces/wihort/links/