Tidewater Gardening - January 2010
Interior Houseplant Care
K. Marc Teffeau
Happy New Year! Can you believe it is 2010? It seems not long ago we were worrying about the collapse of civilization as we know it with the Y2K thing and the arrival of 2000! With not much happening in the outside landscape in January, we settle in and enjoy perusal of all the seed and gardening catalogs that are arriving in the mail. Now, with the advent of promotional e-mails, we can get the catalogs over the Internet.
We can garden inside during January. Our tropical foliage houseplants usually have a hard go of it this time of year because of low light intensities and the low humidity of the interior air. If you are having problems with any houseplant, the first thing you need to know is the name of the plant and its cultural requirements. Check with your local florist, favorite garden center, the garden shelf in the local library or the Internet for information on the care and feeding of the plant.
Light is always a critical factor for houseplants, but it’s especially so during the winter months. The shorter days and lower light intensities during the winter months will result in slower plant growth. It’s important to be aware of each plant’s light needs and provide accordingly. A sunny south or southeast windowsill is good for houseplants that require a lot of light, but be careful that the foliage doesn’t touch the cold windowpane and perhaps get frostbitten. Flowering houseplants require the most light and foliage plants less.
Low light problems can be easily remedied by growing the plants under artificial light. All you need are two 40 watt fluorescent lamps. The best fluorescent lamps are special plant growth tubes that emit the proper quality of color of light. They are sold under various trade names like “Gro-Lux” and can be purchased at garden centers and at hardware and department stores.
To be effective, the fluorescent lamps must be right down at the tops of the plants. Light intensity decreases rapidly even a few inches away from the source. Most plants will do best when the fluorescent lamps are less than 4 inches away. Since fluorescent lamps are cool, there is no problem with too much heat near the plants. For best results, plants should receive 12 to 16 hours of artificial light daily. Make sure you give them at least a 4 to 6 hour dark period daily. Plants don’t “sleep” during this time, they move foods manufactured within the leaves into other parts of the plant.
Because of reduced growth during the winter, houseplants should not be fed as heavily. Most potted plants should be fed regularly between March and October and sort of ignored from November to February. If leaves are smaller and paler than usual it is probably due to the lower light intensities of the winter months. If you have to feed your houseplants, do so with one of the commercially available water-soluble fertilizers. Use it at one-half the labeled rate to avoid encouraging leggy growth.
If your houseplant is having problems, make sure that the source of the problem is not the result of insect damage. Such clues as cottony bits on the stems may mean a mealy bug infestation. Sticky sap and/or brown bumps may indicate a scale problem while grayish or pale green leaves could be spider mites. Treat these problems with an aerosol houseplant insect spray according to label directions.
During the winter months, many houseplants tend to develop brownish spots on the upper sides of the leaves. This is particularly true on African Violets and many succulents. Most of these brown spots are caused by sloppy watering practices. Allowing water to splash on the foliage activates microorganisms that are generally not active when the foliage is dry. The best method of preventing this disease is to always water the plants carefully, making sure that the leaves remain dry.
Another problem is the common leaf spot that appears as a yellow or white ring on the surface of the leaf. The center of the ring generally remains green. Again, this is a result of poor watering practices. The yellow ring is due to the disease just getting started and the white ring is the result of water deposits.
Most houseplant problems during the winter are because of poor growing conditions or incorrect watering. Overall leaf drop may occur when you move a plant from one room to another or drastically change its environment in some way or another. Chilling or exposing the plants to drafts, hot or cold, can cause the same symptoms.
If the leaves are turning yellow and dropping from the bottom toward the top, the culprit usually is over-watering. This damages the root system of the plant. Sometimes the leaf loss problem is the result of over-watering because the plant is in too large a pot. The excess soil around the roots holds too much water, leading to low oxygen levels and root rot. To avoid this problem, don’t put a plant into a pot more than 1 to 2 inches wider than the root ball. Wilting of the plant can also be caused by too much water, too little water or over fertilizing.
Another problem that results in leaf loss is that the air is too dry, especially if you are heating with a wood stove. Humidity around the plants can be raised by a light misting of the leaves once or twice a day with water. The spray bottles are inexpensive and can be purchased at any place that sells houseplant supplies.
Try grouping your plants together in a pan with a layer of small stones in the bottom. Apply water to the pan to cover the stones. This not only provides a bottom source of water, but as the water evaporates from around the stones, it raises the humidity around the plants.
Your glossy-leafed houseplants will benefit from a bath every few weeks. Use a mild soapy water on a cloth to gently wipe each leaf. Then rinse each leaf by wiping with a cloth wet with only water. Dust which accumulates on the glossy foliage of indoor plants detracts from their appearance and shades the leaf surface from maximum sunlight.
There are several old favorite gift plants during the holiday season. We are all familiar with the poinsettia, Christmas cactus and azalea as common sights at Christmas, but others are also popular gifts. The chrysanthemum, kalanchoe, cyclamen, Christmas pepper and Jerusalem cherry are appreciated for the colorful blossoms or fruit.
Some of these plants require special care while others can’t be expected to be “revived” once their blooms have fallen. The Christmas begonia, cyclamen, azalea, Christmas pepper and Jerusalem cherry should be discarded after the blooms or fruit drop. Remember that the fruit of the Jerusalem cherry is poisonous. Its miniature tomato-like fruit might look inviting to younger children, so be sure that your child knows they are not to eat.
Three plants that can be kept over after the holidays are the Christmas cactus, the kalanchoe and the poinsettia. To keep your poinsettia for next season, place it in a dimly lighted room once the bracts or “petals” drop and water it only enough to keeps its roots moist. Don’t be upset if all the leaves yellow and drop. The plant needs to go through a resting period.
In mid April, prune the stems back to a 6- or 8-inch length, leaving only 2 or 3 nodes or joints per stem. Water the plant regularly and place it in a sunny window. When all danger of frost is past, repot your poinsettia in an organically rich soil in a clay pot and plant the pot in a sunny location in your garden. Make sure that the rim of the pot is buried, or it will act as a wick, drying out the soil in the pot and the surrounding soil.
Mulch the area around the poinsettia and feed it lightly. Prune back any overly aggressive shoots. In September, bring your plant inside. Beginning the 1st day of October, give your poinsettia at least 14 hours of darkness a day for 40 days in a row by placing it in a closet from 5 p.m. to 8 a.m. Any interruption of this schedule will delay flowering. You should start to see color in the bracts by Thanksgiving.
Test the soil surface daily. When it feels dry to the touch, water it thoroughly; enough to allow water to drain out of the bottom of the pot. If the pot is wrapped in foil, punch a hole in the bottom to allow drainage. With a little bit of work, you will be rewarded with a flowering poinsettia again at next year’s holiday season.