Marin Master Gardeners
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Houseplants Part 2

January 23, 2012
Nanette Londeree

Keep your houseplants green and growing

If you were the lucky recipient of a houseplant this past holiday season or have decided to take the plunge into indoor gardening, caring for your new additions needn’t be a mystery or cause for brown thumb jitters. If you’ve got the right plant for the location—simulating the light, temperature and humidity the plant would enjoy in its native habitat, along with a suitable container and soil, then keeping your indoor garden in shape just needs a bit of know-how and practice about the basics of watering, feeding, grooming and controlling pests and disease. A piece of cake!

Containers and Soil
The stuff your plant lives in provides support to keep it from falling over, water and nutrient storage, and air for the roots. You can make your own mix with equal parts of good garden loam, organic matter (peat moss, well-rotted manure or leaf mold) and sharp sand or perlite; you can also purchase it pre-made as potting mix.

When selecting a container for your plant, consider size, material and drainage. There are lots of materials to choose from; plastic containers may be better for moisture-loving plants while breathable materials like porous ceramics or wood are best suited to plants that can handle drier soil. The container should be appropriate to the size of the plant—slightly larger than the root ball, and should have at least one hole at the bottom to facilitate drainage.

Watering
More houseplants die from getting too much water rather than too little. Water needs vary and depend on the species and size of the plant, the type of container and soil, and the growing conditions. While consistent levels of moisture are desirable, it’s better to let soil go moderately dry between watering rather than have soggy soil. Water thoroughly; a little water draining out of the bottom of the pot is fine, just don’t let the pot sit in water for long periods of time.

Feeding  
Providing a steady diet of nutrients to plants growing in containers is easiest when using a water-soluble complete fertilizer formulated for houseplants. Mix according to label directions; once a month, April through September, is usually adequate for most non-flowering plants. The plant should be well watered before the addition of liquid fertilizer to prevent damage to roots and leaves. Don’t overfeed; many of the pests that plague houseplants thrive on the lush new growth that results from lots of fertilizer.  

Grooming
Cleaning leaves to remove dust helps to maintain the amount of light the plant receives. Plants with smooth leaves can simply be wiped with a damp cloth while those with hairy leaves can be brushed with a small, soft paintbrush. I find the easiest way to both clean and refresh plants is using the faucet sprayer and rinsing with warm water in the kitchen sink (or the shower for ferns or large plants). If you have some brown portions of leaves (most often a result of low moisture), use scissors to trim away the damaged portion of the plant.  

Repotting  
As your plants grow, they may need to move up to larger containers. If the plant has stopped growing, has visible roots on the surface of the soil or emerging through the drainage hole, it’s time to pot up.  Select a pot a couple of inches larger than the existing one, and use some fresh potting mix when planting.

Managing problems
Most plant related problems are a result of growing conditions—too much or too little water, light, heat or fertilizer—and more easily corrected.  Houseplants are susceptible to some pests—aphids, mealybugs, scale, spider mites and whiteflies are the most common.  All are sucking insects that can be just a simple nuisance or, if left unchecked, cause the demise of the plant. Aphids are small, soft bodied insects ranging from green to yellow to nearly black, and love succulent new growth. Mealybugs tend to nestle in cracks and crevices and look like tiny pieces of cotton. Greenhouse whitefly adults are somewhat gnat-like and covered with fine white wax; you’ll often see little “clouds” of them fly when the plant is disturbed. Evidence of tiny two-spotted spider mites is fine webbing on the undersides of leaves. Soft scale is probably the hardest to detect—they resemble small droplets along twigs and stems, and the undersides of leaves. In addition to their direct damage to the plant, all of these sucking pests secrete sticky honeydew that supports the growth of black sooty mold and attracts ants.  

If pests are isolated to a small portion of the plant, simply prune out the infected area and dispose.  Light infestations can be managed by hand-picking pests, or blasting them with water from a squirt bottle or hose.  A spray with neem oil or horticultural oil may reduce pests by smothering them. Insecticidal soaps are effective for managing aphids, mites and whiteflies.

For mealybugs and scale, a solution of rubbing alcohol (70% isopropyl) can be applied directly on the pest either with a light spray, a cotton-soaked swab or soft infant’s toothbrush, and repeated once or twice at weekly intervals. Be sure to sanitize the entire pot and treat the surface of the soil. If none of these methods work, a systemic insecticide labeled for use on houseplants, may be effective.

You can purchase houseplants at nurseries, home improvement centers, farmers markets, even via the internet. A healthy specimen should have a well-balanced overall form, with blemish-free foliage that is the right color, shape and size for the type of plant. Check for any signs of insects or disease—you don’t want a pest hitchhiking home with you.  

By employing the few basics of care, you’re now on your way to growing healthy and happy houseplants.

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