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Yes, Houseplants Experience Stress, Too

By Steve Cramer, Colorado State University Cooperative Extension

It's springtime outside, but a Gardener's thoughts are never far away from houseplants on the inside. Any good Gardener knows houseplants can suffer stress at any time of the year.

Stress comes when we overwater houseplants, keeping soil constant wet. This can cause root rots that impair a plant's ability to replace moisture loss.

Houseplants also can outgrow their pots. In that case the top of the plant can be out of balance with the amount of soil in which it is growing. Such plants quickly exhaust the supply of water present in the soil and they must be watered more often. But, constant watering sometimes compacts the soil and reduces air space, which, in turn, deprives the roots of adequate oxygen. This can reduce root development and plant growth. Another concern with frequent watering and rapid evaporation rates is accumulation of toxic levels of soluble salts. These salts can interfere with a plant's capacity to pick up moisture and too many salts can first kill leaves and, ultimately, the entire plant. An additional problem of providing too much water is that soil can become "channeled," so water drains too rapidly and fails to thoroughly wet all of the soil in the container.

Hints for the would-be "Green Thumb"

That prized house plant is not the result of any magical rite performed by a rare individual with a "green thumb." It is the result of intelligent selection of plant varieties to match the conditions in which they are to grow. Here are suggestions to improve your house plant growing skills.

  • Determine the conditions, such as light intensities and prevailing temperatures, under which plants are to grow.
  • Determine the types of plants suited to these conditions.
  • Learn as much as you can about specific requirements of the plants you select. Marginal necrosis or scorch usually is caused by toxic concentrations of soluble salts.
  • Purchase well-grown, disease-free plants from a reputable dealer. "Bargain" plants often are poor quality because of diseases and Insects. They may be in soft and succulent condition because of over-fertilization to force rapid growth.
  • Use pots of adequate size. If the plant requires watering more often than once every three to four days, a larger container may be needed or the soil mix may be too porous. Check to be sure the plant is not root or pot-bound.
  • Make sure the container provides adequate drainage.
  • Use clean, sterile pots and pasteurized potting soil.

Pasteurizing soil

You can purchase pasteurized soil or you can process your own. A soil mixture appropriate for most house plants contains three parts good loam (soil), one part organic matter (leaf mold, compost or peat) and one part sand. Expose this soil mix to enough heat to destroy any pathogenic micro-organisms in the soil. Complete sterilization is not necessary and may even be harmful.

For oven pasteurization, place the soil in a small greenhouse flat or a baking pan to a depth not to exceed four inches. (Do not pack the soil.) Moisten the soil if it is not already damp. Avoid over-wetting and puddling. Cover the container with aluminum foil folded over the edges. Insert a thermometer into the center of the soil mix (the thermometer should not contact the bottom of the container), and place this in the over at low heat (approximately 200 degrees F). Maintain the soil at a temperature of 160 degrees F for about 30 minutes. If the soil temperature gets higher than 160 degrees F, remove it from the oven sooner. Allow to cool before using.

Sanitizing pots

Wash glazed pottery containers and plastic pots with detergent and hot water. Wash and scrub porous clay pots, then soak in liquid bleach (two tablespoons per gallon of water) for one hour. After disinfecting with bleach, rinse the container free of any bleach solution.

Photograph courtesy of Judy Sedbrook.

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Date last revised: 01/05/2010