Spring is good time to fertilize houseplants

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Last Updated: 
February 19, 2003

CORVALLIS - Unlike our dogs and cats, houseplants do not need to be "fed" regularly, according to Jan McNeilan, consumer horticulture agent with the Oregon State University Extension Service.

Fertilize, or feed them only when they are actively growing and as needed to maintain moderate growth. Spring is a good time to start fertilizing most houseplants again.

"Most house plant ailments relate to overfeeding, coupled with poor watering practices," explained McNeilan. "The key to success is to feed sparingly and to 'double water' monthly to flush away excess fertilizer salts. To double water, water once as usual, then follow with another watering five minutes later with enough water to cause some to run out the bottom of the pot."

Houseplants need fertilizers containing three major elements: nitrogen (N), phosphorus (P, sometimes listed as P2O5), and potassium (K, sometimes listed as K2O or potash).

Sometimes called "plant food," houseplant fertilizers are sold in granular, coated pellets, crystalline, liquid or tablet forms, under a multitude of brand names. The label should indicate how much water-soluble nitrogen, phosphate or potassium is available per pound of product.

The numbers following the fertilizer name correspond to the percentage of those elements - N, P (P2O5) and K (potash) by weight in the fertilizer.

"The numbers on fertilizer products give home gardeners information about the makeup of the fertilizer and to some extent where the fertilizer should be used," said McNeilan. "For example, a 20-20-20 mixture would be good for stimulating foliage plants, a 10-20-10 might be better for flowering plants. Fertilizer mixtures can be used to stimulate growth, or enhance flowering or to simply maintain the plant."

"Many houseplant fertilizers are rated about 20-20-20," she continued. "If the numbers don't add up to 100, it means there are inert ingredients or other nutrients in the fertilizer. Sometimes there is a fourth number, which is used for sulfur, another plant nutrient."

Commercial houseplant fertilizers should be used according to instructions on the package label, or even more dilute. Frequency of fertilizer application will vary, depending on the vigor of growth you want and the age of each plant. Some plants do best with fertilization every two weeks, while others will flower well for several months without needing any supplement.

Consult a good reference on houseplants to determine the needs of your specific plants.

Author: Carol Savonen
Source: Jan McNeilan