According to the Texas Almanac, Central Texas is due it's first freeze about December 1st of each year, give or take a week or two. This year being an El Niño year, more rain and cooler temperatures are forecast for our area as the jet stream tends a little further south than normal. The one mantra heard repeatedly just before a freeze is to protect people, pipes, pets and plants. If you are one who does not make it a point to check the weather on a daily basis, you may want to go ahead and plan now to wrap your pipes and make a plan of action what to do with your plants. In fact, you may want to bring some of them in now to enjoy the benefit of cleaner air.

In the past houseplants have mostly been considered decorative items to enhance the warmness of the house or to bring a bit of nature into the house. Now there's a growing trend to use some common varieties as indoor air purifiers. Yes, you can purchase an commercial air purifier, but houseplants are much quieter and have greater eye appeal. As it's estimated we now spend about 90 percent of our time indoors, it makes sense to have a clean environment. However, a clean house does not always equal a clean environment. According to WomensHealth.gov, chemicals used for cleaning, pest control, wall paints, hair spray and nail polish remover could compromise your health as they contain volatile organic compounds (VOCs). In addition, building products and pet dander contribute to indoor air pollution that could trigger the following symptoms.

• A tired feeling.
• Irritation of throat, eyes or nose.
• Dizziness.
• Headaches without stress.
• Having trouble breathing.

Conclusions from a 2009 study published in the New England Journal of Medicine pointed to, "A reduction in exposure to ambient fine-particulate air pollution contributed to significant and measurable improvements in life expectancy in the United States." It is known that pollution may cause asthma or make it worse, the exact cause of asthma is not completely known. It is believed to be partially inherited, but it also involves many other environmental, infectious, and chemical factors. About 20.5 million people in the US have been diagnosed with asthma, with at least 6.2 million of them children under the age of 18. Asthma is the third ranking cause of childhood hospitalizations under the age of 15.

Which Plants Work Best?

Kamal Meattle, a researcher from New Delhi, has created a model for cleaner air in homes and office buildings. Through his TED presentation, Kamal discussed the use of three common houseplants that can greatly contribute to cleaner indoor air.

• The Living Room Plant or Areca Palm (Chrysalidocarpus Lutescens). This plant removes CO2 from the environment and converts it to oxygen.
  
  
• The Bedroom Plant or Mother-in-Law's Tongue (Sansevieria trifasciata). Called the Bedroom Plant as it converts CO2 into oxygen at night.
  
  
• The Specialist Plant or Money Plant, also known as Pothos and Devil's Ivy (Epipremnum aureum). A common plant found in homes and office buildings, this ivy is called the Specialist as it removes formaldehyde from the environment. The plant is listed as "toxic to cats, toxic to dogs" by the ASPCA, due to the presence of insoluble calcium oxalates. If your dog or cat is prone to tear up plants, you will want to avoid this one.
  
  
• Spider Plant (Chlorophytum comosum). A very easy plant to grow and maintain, the spider plant also reproduces frequently by sending out shoots with baby plants attached. Studies have shown that spider plant is quite effective in cleaning indoor air by absorbing chemicals including formaldehyde, xylene, benzene, and carbon monoxide in homes or offices.

Answers to Some Common Questions

Plant Answers, an archive of gardening information provided as a service by Texas Cooperative Extension, is a must visit if you have questions pertaining to indoor and outdoor plants in Texas. Here are a few common questions and answers.

Q. How can I tell if my houseplants are getting the right amount of light?

A. One of the most common signs of inadequate light is yellowing, dropping leaves. That is also one of the most common signs of too much light. To figure out if either of these situations is your problem, you will have to look more carefully at your plants.

Flowering plants that don't flower, any plants with leaves angled toward the light and long, spindly stems, plants such as coleus whose red pigments have faded, or plants whose new leaves are smaller are all showing signs of inadequate light. Either move these plants to a brighter spot or supplement natural light with artificial light.

Foliage plants require nothing more than an inexpensive, cool, white fluorescent lamp; combine a cool white lamp with a warm red lamp to ensure the best bloom in flowering plants. When your plant's leaves show signs of overall yellowing or have large spots of dry, dead tissue known as leaf scorch or leaf burn, the problem may be too much light. Use a diffuser curtain to reduce the amount of direct sunlight hitting the plant, or move it further away from the window.

Even if the light level is correct for a given plant the same symptoms may develop if it was moved straight from a low light intensity to a much brighter spot. Make such moves gradually to allow the plant to adjust to the new light levels.

Q. It gets very dry in my house in the winter. Does this hurt my plants? What can I do to help?

A. Most plants prefer a relative humidity of 50-60%. During the winter, most homes have a relative humidity of 10-15%. Low humidities such as these can cause plant leaf edges and tips to brown, flower buds to brown and fall off, and keep the whole plant from thriving. The best solution is to use a humidifier of some sort to raise the relative humidity of the whole house or the room where the plants are located. This will not only help the plants but will make the house more comfortable for human inhabitants. If this is not practical, try growing the plants in the kitchen or bathroom, where the air is naturally humid.

Small plants can be grown in a terrarium, where humidity levels are easily kept high. Place plants in groups where the water vapor given off by each plant benefits the others. Even better, group the plants on a tray of moistened pebbles or long-fibered sphagnum moss. This will raise the local humidity to an acceptable level. Misting the plants once or twice a day helps, but is really a very short-term remedy.

Q. When should I repot my indoor foliage plants? How do I go about it?

A. Permanent houseplants usually need to be repotted annually until they attain their final size. The best time for this procedure is during a slow growth period, which will be during early spring for most plants. Check the drainage holes of the pots to see if any roots are showing. If so, the plant is probably potbound and needs repotting. For best growth, the plant should be moved to a pot that has a diameter 1 to 1 1/2 inches larger than the one it is presently growing in.

Cover your work area with newspapers. Prepare the new pot with a layer of potting soil at the bottom that is deep enough to hold the plant at the desired height. Place your hand over the old pot with the plant extending between your fingers. Turn it over and gently knock the root ball out of the pot. Place the plant in the larger pot then pour potting soil around the root ball. Tamp or firm the soil gently with your finger tips as you fill the pot. Cover the root ball to the same depth it was previously. Leave 1 to 1 1/2 inches of pot rim above the soil to facilitate watering. Water thoroughly. Place the plant in a low-light area for a few days, then return it to its normal location. Do not apply any houseplant food for several weeks as the new potting soil will meet the plants needs.

Q: When can houseplants be moved outside?

A: It is best to wait at least until the last frost free date. Better to wait until middle of April.