Fall/Winter Houseplant Care

Toddler Jungle

 As the weather turns cooler, we begin to pay more attention to horticultural chores in the great indoors. Houseplants need a bit of TLC right now, as they adjust to the change of seasons. (Note: "TLC" = tender loving care. Do not place houseplants in front of a TV tuned to the TLC Channel showing "Toddlers & Tiaras" or "19 Kids and Counting"; their leaves will turn brown.)


 Houseplants tend to slow down their growth cycles now, so their food and water requirements are less.

Many houseplant aficionados won't even feed their houseplants now, and won't resume a monthly fertilization until next spring. And because houseplants use less water now, change your irrigation habits. 

Poke your finger or a moisture meter into the soil of a houseplant to make sure that the top few inches have dried before you add water. Another way to determine if your houseplant is in need of water: lift the pot. If it is as heavy as it was when you last watered, wait. When the soil has dried, that pot will be a lot lighter, a good sign that it's time to pour it on.

Dracaena 'Janet Craig'

During fall and winter, the sun is lower in the horizon. Help your houseplants cope with this lower level of light by moving them a bit closer to a sunnier window.

        









There are some indoor plant pests that may be moving into your house this time of year. Aphids, spider mites, whiteflies, fungus gnats and scale are among the pests that are taking up residence with you, especially if your houseplants have spent any time recently outdoors or are new purchases. A couple of good books about houseplants, including lots of pictures of plants and pests, are "The Complete Houseplant Survival Manual" by Barbara Pleasant and "Successful Houseplants" by Ortho Books.

        And one reader is wondering about how to control another common houseplant pest. From the garden e-mail bag, Cynthia writes: "I have an indoor coleus plant in my bathroom, which gets indirect sunlight. All was well until yesterday when I discovered little oblong or rectangular-shaped, white, fluffy somethings on the plant. What are they and how do I eradicate them?"
        

     Those "fluffy somethings" might be mealybugs. These soft-bodied sucking insects are about one-eighth of an inch long, and are covered with a whitish, cottony wax. They especially like to congregate on the backsides of the leaves of houseplants, where the leaves meet the stems.

        There are several steps you can take to control mealybug populations on your houseplants.

Step One: wash off the plant, especially the underside of the leaves, in the sink with a forceful stream of lukewarm water. Doing this once or twice a week for a few weeks may take care of the problem. 

Step Two: Dip a cotton swab in rubbing alcohol and remove the mealybugs by hand. Tweezers can help dislodge the ones you can't reach  with a cotton swab. 

If those two techniques don't do the job, apply insecticidal soap or a narrow-range horticultural oil to the infested plant area. But be careful: make sure your plant won't be damaged by the soap or the oil by testing it on a small, out-of-the-way part of the plant first. The Marin County Master Gardeners also offer this advice: If you’ve got mealybugs on your houseplants, be sure to sanitize the entire pot and treat the surface of the soil.  Also manage for ants.

And yet another way to control houseplant mealybugs: According to Sacramento County Master Gardener Lori Ann Asmus of Emerald City Interior Landscape Services, scrape away and replace the top inch of soil in the potted plant. That can help eliminate future mealybug populations.

Fungus Gnats on Houseplants: How To Control Them

 Winter's rain, snow, wind and cold tends to turn a gardener's attention to the indoor jungle, and the creatures that are hiding there.

From the garden e-mail bag, Nickie asks: "I have a question for you about the little gnats that seem to come from some of our house plants. How do you get rid of them? Why do the plants produce them?"
  

Those are fungus gnats that live in the soil surrounding the house plant, although the adults sometimes can be found on the plant leaves. They thrive in soil that is overly moist, filled with partially composted materials and rich in organic matter. You may notice that these critters tend to come up to the surface when you water the plant thoroughly. If there are a lot of fungus gnats, you may even notice a slime trail on the top of the soil.




The larvae of fungus gnats chew on plant roots, causing stunting or plant decline. The adults can spread other plant disease problems.
 

How did the fungus gnats get to your potted plants? Although they possibly flew to that location, more than likely they were in the soil when you either purchased the plant or repotted it in a bigger container with more soil, especially if that soil contains homemade compost or moist, backyard dirt.

         If fungus gnats are bugging you, take them to a shady area outside for a short time on a nice day (or the garage, on a not-nice day). Water the plant thoroughly in a deep pan. When you see the gnats rise to the surface, scrape off the top inch of soil into the pan, then to the trash. Replace that soil with fresh, bug-free potting mix. 

Then, apply the biological insecticide Bacillus thuringiensis subspecies israelensis (Bti). This will control any fungus gnat larvae that are still in container media. You may need to repeat this application every five days until the problem is under control. Commercially available nematodes (especially the Steinernema feltiae nematode) can also control fungus gnat populations. Among the sources for nematodes: Peaceful Valley Farm Supply.

 To control future fungus gnat outbreaks:

• Make sure your window and door screens are secure.

• Let the surface of your houseplant soil dry out between waterings.

• Make sure the container has good drainage.

• Get rid of any standing water in the saucer below the pot. 

• If you are using homemade compost in your potting soil mix, heat it in the oven first to kill off any fungus gnat eggs.

 Colorado State University Cooperative Extension offers these suggestions for using heat to sterilize the soil:

Oven Method - Spread soil not more than four inches deep in non-plastic containers, such as seed flats, clay pots and glass or metal baking pans. Cover each container tightly with aluminum foil. Insert a meat or candy thermometer through the foil into the center of the soil. Set the oven between 180° and 200° F. Heat the soil to at least 180° F; keep at this temperature for 30 minutes. Do not allow the temperature to go above 200° F. High temperatures may produce plant toxins. After heating, cool, remove containers from the oven and leave aluminum foil in place until ready to use. The heated soil will give off an odor.

Microwave Oven Method - Microwave soil for 90 seconds per kilogram (2.2 pounds) on full power. Don't use metal containers and aluminum foil when using a microwave.

Or, get new potting soil. Use only pasteurized container mixes for your house plants.Then, be sure to store any excess potting soil in closed containers. 

• Avoid fertilizing with excessive amounts of manure, blood meal, or similar organic materials. 

• Adding an inch of coarse sand on the top of the soil can also deter fungus gnats.


• A  Yellow Sticky White Fly Trap, placed upright in the container, is another way to monitor the adult fungus gnat population.


• What about synthetic insecticides? Sprays that include active ingredients such as bifenthrin or permethrin are often effective and persistent. However, they are more toxic to beneficial insects. Because of that, some experts advise that when using these on houseplants, move plants outdoors for treatment and wait about a day after application before bringing them back inside. Um, frankly, do you want your houseplants outside, overnight, in the winter? Not a good idea. It's a shock to their system to be outside in the first place. And you don't want to be risking that the spray might drift onto pets or children indoors. So, bypass these sprays.

         The Integrated Pest Management experts at UC Davis offer this fun way for any junior scientists in your household to help you monitor future fungus gnat populations in your plants:

• Bury one-inch cubes or slices of peeled, raw potatoes into your house plant soil, about 3/8 of an inch deep.

• Once or twice a week, unearth and examine the underside of each potato and the soil immediately beneath it. Keep a chart of the numbers of larvae found before and after any treatment to determine whether larvae are being controlled.

• You'll know if they are the fungus gnat larvae if they have a shiny black head and an elongate, whitish to clear, legless body. 





 
Adult fungus gnats, on the other hand, are about one-eighth of an inch long with wings, slender legs and antennae that are longer than their heads. 



• Discard the potato along with the fungus gnats; add a new piece to continue the experiment.


Science!

How Much Light Do Houseplants Need?

How much light do houseplants need in order to grow and thrive? Probably more than you're providing. The limited number of houseplants that can live in low level light (Cast Iron Plant, Chinese Evergreen, Dracaena, Peperomia, Pothos, Sanseveria and the ZZ plant) still need more light than what is found in a typical room: 50-250 foot candles. And those plants will thrive with 200-250 foot candles, but limp along with anything less than that. (Foot candles: a unit of measure of the intensity of light falling on a surface, equal to one lumen per square foot)

A few ways to measure the light in a room:

• Get an inexpensive multi-purpose plant meter that registers light, moisture and pH. Key word in that previous sentence: "inexpensive", as in "I hope it lasts a week" or "Please be somewhat accurate".

I took my $20 multi purpose plant meter to the various houseplants we have here. The shocking news: at noon, in a brightly lit room with a southern exposure, those plants were receiving about 25 foot candles of light.

• Measure the light with the chart contained in this link from the University of Missouri. Their report, "Houseplant Light", states that one way you can estimate the amount of light available is to calculate the number of watts available per square foot of plant area. Low-light plants should receive between 10 and 15 watts of fluorescent light per square foot of growing space. A single fluorescent tube, such as a 2-foot 20-watt tube or a 4-foot 40-watt tube without any other light provides only enough light for plants in this category.

If your houseplants are getting light assistance only from a nearby table lamp or a ceiling fixture, don't be surprised if that calculation shows less than 40 foot candles. 

• And this really simple, but scary light test from the Christian Science Monitor:

 "On a sunny day, get a piece of white printer paper and place it where you want to put a new houseplant. Then hold your hand 12 inches above the paper. Can you see an indistinct shadow? If so, that's low light.
If the shadow is a  bit fuzzy but mostly looks like a hand, that's medium light. A clear hand shadow indicates a high level of light."

I tried this. In many areas of the house, I saw NO shadow, or a dark, fuzzy image, at best. Oh, those poor houseplants.

Fortunately, my abode is populated with easy care houseplants, which I've talked about before here.

Bottom line: My houseplants are alive...but certainly not putting on any growth spurts. They are not going to get any more light. So, I won't stress them with fertilizer (as per this report from the University of North Carolina). Watering is limited to once a month, perhaps twice a month in the summer. Tough love.

If you want to coddle your houseplants, or expand the variety that will thrive in your house, here are a few tips from the University of Missouri:

• The amount of light necessary varies with each plant. In general, the light fixtures available for home plant lighting make it practically impossible to produce too much light for most plants.

• Plants that can adapt to interior settings usually are divided into three general categories: those suitable for low, medium and high light intensities. The categories generally indicate the minimum light required. Growth is often best at the higher end of these suggested light ranges.

• Plants referred to as low light intensity plants generally should receive between 50 and 250 foot-candles. 

• Medium-light plants
 prefer 250 to 1,000 foot-candles. Best growth occurs above 750 foot-candles unless plants also receive extended periods of direct sunlight. Give them artificial light in the 500 to 1,000 foot-candle range or 15 or more watts per square foot of growing area. 

• High-light plants generally are less satisfactory for growing under artificial lights in the home. However, if you want to try, use special high-intensity lamps. These plants need at least 1,000 foot-candles, or 20 watts per square foot of growing area, but should have higher intensities for best growth and flowering. Fixtures containing three to four fluorescent tubes are necessary for plants requiring high light.

• As a single light source for plants, incandescent light bulbs are not particularly good. They are a good source of red rays but a poor source of blue. They produce too much heat for most plants and, if used, must be located some distance from the plants, thus reducing the intensity of the light the plants receive. They are also about one-third as efficient as fluorescent tubes in converting electrical energy to light.

• Cool white fluorescent tubes provide one of the best artificial light sources available for plants in the home.

• Special fluorescent tubes also have been developed for growing plants. These have a higher output in the red range to balance the blue output. Many home gardeners have found that these tubes can be used in combination with cool-white tubes. Use one special plant-growing tube to each one or two cool-white tubes. This method is more economical than using all special tubes, since cool-white tubes cost less than the special plant-growing tubes. 

• Most plants should be located with the tips of the plants 6 to 12 inches from the light source. The intensity of light drops rapidly as the distance from the light bulbs or tubes increases.

• The brightest spot under a fluorescent fixture is directly beneath the center of the tubes.

• The light fixture's position should be adjustable so you can keep the distance between the light and the plant fairly constant.
 

• In most cases, plants receiving no outdoor light should be lit from 16 to 18 hours each day. If some additional light is received, 12 to 14 hours each day may be adequate.
 

• Space plants far enough apart to allow light between them. Arrange plants so they do not shade each other. Keep tubes clean and replace old tubes promptly.

There are a lot of houseplant lighting systems available. Choose one that is right for the requirements of your most finicky houseplants. Or not. Tough love.

Your Houseplants are Screaming: "You Call This Food?!?"

This was going to be a rant on houseplant fertilizers. I was about to dump on the folly of the latest marketing innovation in houseplant food: the drip feeder. 

These inexpensive (about $1.50), hypodermic-like IV's for houseplants only offer miniscule amounts of nitrogen, phosphorus and potassium, and only for a short time, about two weeks. On the plus side when it comes to houseplants, these mini-meal drippers (which put your plants on a less than 1% N-P-K diet...wayyyyy less than 1%) are healthier that the big buffet offerings of a typical, water soluble plant food that may offer up to 20% N-P-K. 

Huge, salt-based meals like that for houseplants usually result in weak growth, root rot, leaf burn, salt deposits and the dropping of lower leaves.

The big problem with these one-ounce fertilizer drippers, which are intended to be used in an eight-inch pot? All the fertilizer is going to a very small area of the plant roots. One ounce of a liquid, dripping out at the rate of a few drops a day, is not going to percolate throughout the entire rootball. Yes, watering the soil before adding the dripper (as recommended on the label) will help spread the fertilizer. But not enough to nourish all the roots. Or even reach the bottom of the container. And the few roots the liquid does reach? Root burn could still occur, since it is dripping in a very small area. 

And seeing how the N-P-K content of these dripper products is measured in the hundredths and thousandths of one percent, you may be providing more nutrients by "feeding" your houseplants...tap water!

Texas A&M University advises to go easy on the fertilizer, following label directions. "When applying fertilizer in a solution, make sure that some runs out of the bottom of the pot. This prevents root burn and the buildup of soluble salts or excess fertilizer and reduces the chance of burning the plant."

An Ohio State University report concludes that the best way to fertilize houseplants is to... "fertilize at half the recommended strength, every 2 weeks from March to September. Do not fertilize most plants during winter months. Winter's reduced light and temperature result in little or no growth. Most houseplants are dormant during winter."

But, as always, the more I researched the topic, the more I realized there is a lot more to learn, including this surprising tidbit from the Horticulture Department of North Carolina State University: 

"Houseplants grown under less than 200 foot candles (a measurement of light intensity) benefit little from fertilization and may actually be harmed." 

Yes, there are good arguments for NOT fertilizing houseplants in low light situations. And your house, if typical, is probably well below that 200 foot-candle threshold. You may be slowly killing your houseplants with too much food and too little light.

Next time: how to measure the amount of light in your house, using ordinary household items. And, choosing houseplants that do best in low light conditions.

Cold Weather Houseplant Care

        

As the weather turns cooler, we begin to pay more attention to horticultural chores in the great indoors. Houseplants need a bit of TLC right now, as they adjust to the change of seasons. Houseplants tend to slow down their growth cycles now, so their food and water requirements are less.

        Many houseplant aficionados won't even feed their houseplants now, and won't resume a monthly fertilization until next spring. And because houseplants use less water now, change your irrigation habits. 

     Poke your finger or a moisture meter into the soil of a houseplant to make sure that the top few inches have dried before you add water. Another way to determine if your houseplant is in need of water: lift the pot. If it is as heavy as it was when you last watered, wait. When the soil has dried, that pot will be a lot lighter, a good sign that it's time to pour it on.

        During fall and winter, the sun is lower in the horizon. Help your houseplants cope with this lower level of light by moving them a bit closer to a sunnier window.

        There are some indoor plant pests that may be moving into your house this time of year. Aphids, spider mites, whiteflies, fungus gnats and scale are among the pests that are taking up residence with you, especially if your houseplants have spent any time recently outdoors or are new purchases. A couple of good books about houseplants, including lots of pictures of plants and pests, are "The Complete Houseplant Survival Manual" by Barbara Pleasant and "Successful Houseplants" by Ortho Books.

        And one reader is wondering about how to control another common houseplant pest. From the garden e-mail bag, Cynthia writes: "I have an indoor coleus plant in my bathroom, which gets indirect sunlight. All was well until yesterday when I discovered little oblong or rectangular-shaped, white, fluffy somethings on the plant. What are they and how do I eradicate them?"
        

     Those "fluffy somethings" might be mealybugs. These soft-bodied sucking insects are about one-eighth of an inch long, and are covered with a whitish, cottony wax. They especially like to congregate on the backsides of the leaves of houseplants, where the leaves meet the stems.

        There are several steps you can take to control mealybug populations on your houseplants. Step One: wash off the plant, especially the underside of the leaves, in the sink with a forceful stream of lukewarm water. Doing this once or twice a week for a few weeks may take care of the problem. Step Two: Dip a cotton swab in rubbing alcohol and remove the mealybugs by hand. Tweezers can help dislodge the ones you can't reach  with a cotton swab. If those two techniques don't do the job, apply insecticidal soap or a narrow-range horticultural oil to the infested plant area. But be careful: make sure your plant won't be damaged by the soap or the oil by testing it on a small, out-of-the-way part of the plant first. According to Lori Ann Asmus of Emerald City Interior Landscape Services in Sacramento, scrape away and replace the top inch of soil in the potted plant. That can help eliminate future mealybug populations.