OVERWINTERING HOUSE PLANTS

Don't kill them with kindness

In our efforts to make our plants as comfortable as possible, we sometimes overdo it.

It's coming onto winter, and here at the little studio on the hill our nighttime temperatures sometimes dip down into the mid to upper 20s. So we're bringing in some of the more tender plants and starting to get them ready for overwintering indoors.

One of the questions I get asked the most this time of year is "How do I keep from killing my houseplants!"

And it's a tough environment for a houseplant to find itself in. The heater is turned on, the windows are shut up tight, there's less light for shorter periods every day...a whole laundry list of challenges face houseplants in the very artificial environment of a winter indoors. The best thing to do is learn about the plants' growing conditions and needs, then recreate those conditions as closely as possible.

Here are the GreenMan's 5 Problems to Avoid in Overwintering Houseplants.

THE FIRST PROBLEM IS ALL ABOUT WATER.

Over watering has got to be the number one killer of houseplants. Roots need to have oxygen, and if the soil in a container is saturated the roots could rot.

To prevent this, don't automatically water your houseplants on any kind of schedule. Check them regularly, yes, and if the soil is dry below the first inch or so, then water them thoroughly.

You want the soil to be at what's called field capacity: Completely moist throughout with no dry pockets and no extra water anywhere. To get your soil to field capacity, water the entire surface of the soil until water is running out the drainage holes in the bottom of the container. I take my plants to the sink and just let them drain at a slight angle for a half hour or so. Gravity will drain out all the excess water- the soil will be left holding as much as it can handle an no more, with plenty of spaces for oxygen for the roots. That's Field Capacity.

If you're repotting plants or putting new ones into containers for the first time, be sure to use a light, fluffy potting soil rather than garden soil. Its sterile, so there's less chance of bringing in soil born diseases. And it reaches and maintains field capacity more efficiently.

Salt build up.
When you just dampen the soil in your houseplants, it can lead to the build up of salts and minerals, which are dissolved in water or added as fertilizer. Soil has a tenancy to attract and hold these minerals. A good flushing dissolves the salts and carries them away.

Keep and eye out for a white crust building up on the surface of the soil, or along the edges where the soil meets the container. If you see this crust starting to form, go ahead and give your container a long, slow flushing with running water at room temperature, allowing the water to flow out of the drain holes and into a sink or bathtub.

For a heavy salt build up you may want to drench the plant once or twice more. After it's thoroughly drained, wait for the soil to achieve that one-inch-below-the-surface dryness before watering it again.

Low winter humidity
If you're like me once that heater comes on my sinuses start getting stuffed up, its hard to breath, my skin starts to dry out. That's a sure sign the humidity levels are getting lower.

Now most of the species we consider houseplants today have adapted over millions of years to hot, humid rainforest or jungle environments. Most likely even the ones you have started life in a nice, moist greenhouse...so they're not used to conserving moisture leaving from their big, thin leaves.

To give them a more humid environment, start by placing them close together. As they transpire moisture out their leaves the grouped plants form pockets of higher humidity on their own.

For a higher humidity, get a shallow pan or tray and fill it with pebbles. Place the plants' containers on the pebbles and fill the tray with water. Remember the water shouldn't be deep enough to reach the bottoms of the containers.

You can also spray some plants with a fine water mist. Bromeliads for example take up water through their leaves. But plants with hairy leaves, like the Velvet Plant (Gynura aurantiaca) or African violets (Santpaulia hybrids) tend to hold water and dry out slowly. Keeping their leaves wet could lead to disease problems.

Remember, misting doesn't take the place of the thorough watering we talked about, and you should try to cut back on misting after your plants have had a month or so to adjust to the indoor environment. Instead, try bringing up the overall humidity in the plant room by running a humidifier. Humans and plants seem to be pretty comfortable in winter with a humidity of about 50%.

THE SECOND HOUSEPLANT PROBLEM IS LIGHT
You tend to think of plants using fertilizer as food- but that's only the raw material. The true miracle of plants it the way they turn light energy into food. It they don't have light, all the fertilizer in the world is useless.

Plant leaves contain special cells called chloroplasts that turn light energy into food. Plants that thrive in bright light usually have thicker leaves with lots of chloroplasts. Low light plants have thinner leaves and fewer chloroplasts. But plants also have the ability to adapt to the changes in light levels that occur through the seasons, or when you move to different light conditions. It's called acclimatization.

A high light plant will lose a great many chloroplasts and often drop leaves in response to lower light levels. By the same token, you could expose a low light plant to too much light indoors by placing it in, say, the unfiltered harsh afternoon light of a west-facing window. Most plants will do well in the soft morning light of an east facing window.

In the winter, a south facing window will let in brighter, more direct sunshine because the sun is lower in the sky. Reserve south facing windows for your high light plants. On the other hand, the north light that was adequate for low light houseplants in the summer may be a good place for flowering plants or cacti, that need a cool rest period in the winter in order to set flowers in the spring.

There are all kinds of fancy meters you can buy to measure the intensity of the light on a given plant. But I use a simple technique I call "The Shadow Knows!" Hold your hand close to the plant. If it casts a barely discernable shadow, you're in low light. A well-defined shadow means medium light, and a sharp, high-contrast shadow means bright light conditions.

If you don't have a lot of greenhouse-quality windows in your place, or you'd just like to have more plants than you have windows for, you can supplement with artificial light.

Regular incandescent light bulbs tend to give off a lot of heat and a very yellow or warm red light. Plants prefer light further into the green and blue end of the spectrum- which is why florescent lights are perfect for plants. You can use traditional tubes in an inexpensive shop light, or the new coiled lamps that screw into ordinary threaded incandescent bulb sockets.

You'll need to experiment a little with how much light a plant needs. There's some kind of mathematical formula for figuring how much light drops off with distance, but just remember the further away the light is the lower the intensity. But as supplemental light for mature high light houseplants, don't get the lights much closer than six inches. Medium- and low-light plants should be 12 inches away.

The Shadow Knows test works well for artificial light too. You'll also want to get a timer for your artificial lighting. Aside from being more convenient than having to turn the lights on and off by hand, timers let you regulate the photoperiod for the plants. Photoperiod is simply the length of time a plant is exposed to light, followed by a time of darkness.

Spring-blooming plants are stimulated to flower based in part by lengthening photoperiod as the days grow longer. Fall-blooming plants get their signals to develop flowers by shortening days and lengthening nights.

Some plants like the Christmas Cactus and poinsettias won't bloom at all without extended periods of absolute darkness. But as a general rule of thumb, I set my timers for most all of my houseplants at 14 hours, about 5 a.m. to 7 p.m. The lights kick on shortly before the morning sun comes streaming into my windows and extend the light well past the early sunset, which is happening these days around 5 p.m.

THE THRID PROBLEM FOR HOUSEPLANTS IS DRAFTS-HOT AND COLD
Don't place your plants in cold drafts, such as near doors that are frequently opened to the outside or near poorly insulated windows. As far as the plant's concerned it's just like leaving it unprotected outside.

Same for putting them too near heating vents or radiators. The radiant heat or heated air blowing over the plant will speed drying out and could even burn the leaf tissue.

THE FOURTH PROBLEM IS LETTING A PLANT BECOME ROOTBOUND
When a plant has outgrown its container, the roots start to circle around the inside of the pot.Signs of compacted root growth include slow growth, quick wilting after flowering, yellow lower leaves, small new leaves, and roots growing through the drain hole.

Rootbound plants also seem to dry out more quickly because there are more roots than soil to hold water.

Loosen the plant and gently tip it out. Catch it in your other hand, with the foliage peeking between your fingers and the root ball held in your palm.

Loosen the roots at the base and along the sides of the root ball with your fingers. Then split the lower third of the root ball with a sharp knife. This encourages new roots to grow outward and down, rather than to keep spiraling. Prune off any dead or damaged roots.

Center the plant in its new, larger container, and adjust the soil level so the top of the root ball is about 1/2 inch below the rim of the pot.

Sprinkle new potting soil in around the plant and firm it with your fingers.

Settle the soil and give it good contact with the roots by a deep thorough watering to field capacity.

THE FINAL PROBLEM IS PESTS
Indoor pests multiply quickly. It's warm, it's moist and there aren't any natural predators to keep them in check. They can run rampant in no time. A bad infestation of critters can overrun a plant in days and could do so much damage the plant might never recover.

Since prevention is the best cure, try to get your plants free of pests before you bring them inside. Spray them off with a hard, fine spray from the hose, and repeat the deluge in a couple of days to catch any stragglers that could have been hiding in leaf crevices.
Smaller plants can be dipped in a sink full of luke warm, soapy water. Wrap the container and cover the soil with a tight plastic bag first to keep the soap from infiltrating the soil.

Here are some common houseplant pests and the signs they leave to keep an eye out for.

SPIDER MITES. These little devils are among the most dreaded of pests. They're about the size of a pinhead, and not really insects but more closely related to spiders.They leave a distinctive cottony webbing, especially on the inner joints and undersides of leaves. They thrive on plants that are stressed due to dry conditions such as you find indoors in winter.
Under a magnifying glass spider mites can be black, red, yellow or colorless. Tap a leaf you suspect is infested over a white card. Spider mites that fall from the leaves will look like tiny, moving specks on the card.

APHIDS. Have you ever seen the old Star Trek episode "The Trouble With Tribbles"? Dr. McCoy found the profilic little furballs were "...born pregnant. Which seems to be quite a time saver!" Well, aphids are a gardener's tribble. They are born pregnant and if you have one aphid, you have dozens. These guys run in gangs.
Aphids look like green, yellow, black or white spots that cluster tightly, usually near the ends of stems, around new growth...although they can appear anywhere on a plant. They have two little projections on the rear that I call "tailpipes."

Aphids and spider mites are soft-bodied bugs that can often be blasted off plants with a hard stream of water. They also respond to direct applications of insecticidal soap, which dries their bodies out. The soap spray has to contact them directly, though. Just having it on the foliage of plants won't have any effect.

Lady bug larvae (Hippodamia convergens), Lacewing larvae (Chrysoperia carnea) and predatory mites (Amblyseius cucumeris) are effective, natural controls for these pests.
See Resources at the end of this article for sources of lady bugs and predatory mites.

MEALY BUGS. These show up as white cottony tufts attached to the joints of plant stems. Infested plants look like they're drying out even when they have sufficient water. If you catch the problem very early you can apply rubbing alcohol to the bugs with a cotton swab... but often by the time you notice them the infestation is very bad. Hard as it might be, the best thing would be to get rid of the plant and watch your others for signs the mealy bugs have spread.

SCALES. Scales are the barnacles of houseplants. They attach to leaves and form a tough, waxy shell over themselves that resists most everything you use to get rid of them!

When they're young they are unprotected as they move around on the plant and vulnerable to insecticidal soaps. Once in place with their shields up, about the only thing that will work is physically scraping them off with a fingernail. Like an infestation of mealy bugs, you may just have to get rid of a scale infested plant to keep the problem from spreading.

My friend Bill Radler and I chatted about indoor insect pests recently- here's what he does about them.

If you're like me, your home isn't complete without houseplants. Overwintering them inside helps us both- they survive and thrive another year and I get to enjoy learning about them and caring for them in another kind of gardener/plant relationship. Give these tipsa try this winter. Come about the end of February, you'll be glad you took the time to learn how to keep your indoor garden in top shape.

RESOURCES http://www.planetnatural.com http://www.planetnatural.com/site/lacewing-larvae.html http://www.planetnatural.com/site/thrips-predator.html http://www.gardensalive.com http://www.gardensalive.com/product.asp?pn=5065 http://www.gardensalive.com/search.asp?ss=lacewing