Don't forget to fertilize houseplants in spring

Last Updated: 
April 30, 2008

AURORA – During your spring gardening frenzy, don't forget to fertilize your houseplants. All plants, including those kept indoors, need nutrients in the spring.

But take care to not feed them too often or too much.

"Most house plant ailments relate to overfeeding, coupled with poor watering practices," explained Jan McNeilan, consumer horticulturist with the Oregon State University Extension Service.

"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 fertilizer is sold in granular, 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 house plant fertilizers are rated about 20-20-20," she added. "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 diluted. 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.

Author: Carol Savonen
Source: Jan McNeilan