Houseplants grow under artificial conditions. They are confined to a pot and cannot search for nutrients. Therefore, the gardener must provide the necessary fertilizer. That being said, remember: Overfeeding is far worse than underfeeding.

        If the plant is overfertilized, the foliage will turn yellow, burn and drop off prematurely because the salts have damaged the roots and cut off the water supply. The cure is to stop fertilizing, remove the upper crust of the growing medium and allow the salts to leach out.

        Underfeeding also poses problems. Signs of too little fertilizer are a general yellowing of the entire plant and little or no new growth.

        To correct these two situations, pay attention to the potting medium and supplementary fertilizing. Potting mediums are usually of two kinds: peat-based and soil-based. Without exception, I use peat-based potting mixes. Peat-based mixtures come fortified with nutrients, and you don't have to worry about supplementary feeding for about six weeks. If you buy a plant from a nursery, I suggest waiting two weeks before feeding.

        Never apply fertilizer to a dry plant. If in doubt, water first, then apply fertilizer. Never apply fertilizer to a dormant plant; wait until you see signs of growth before you begin to apply food.

        The three principal elements required by any plant are nitrogen, phosphorus and potash. Nitrogen is necessary for leaves and stems; phosphorus for healthy roots; potash assists with the production of flowers. Most houseplant fertilizers are complete — they contain a percentage of the three basic elements. As a general rule, feed plants from spring to autumn. Exceptions include winter-flowering plants, such as primulas, azaleas, and poinsettias.

        Fertilizers come in many forms, including powders, granules, spikes, liquids and tablets. Whichever form you select, be sure to follow label instructions. Never double the dosage because you think the amount is too little. I always fertilize (if necessary) when I water and I fill the pot to the rim, allowing the excess to drain out. Slow-release fertilizers — if mixed into the potting medium when you repot or plant — will give good results because the nutrients are evenly distributed. Osmocote can provide nutrients for up to 12 months. If you use slow-release fertilizers, you will not need additional supplements.

        If you grow a large number of houseplants, it's a good idea to keep a written record or to label the plants that have been fed.

        One final reminder: Never use foliar feeding (applying fertilizer directly to the leaves with a sprayer) as a major program. Occasional misting is useful — as a boost — to plants that are being fed in other ways. I mist my houseplants with plain water throughout the dry, winter indoor months simply to provide humidity; I go easy on additional fertilizers until spring arrives.

        Contact Tim Morehouse by Web site: www.getmoregarden.com; mail: c/o Cincinnati Enquirer. (If writing, enclose a self-addressed, stamped envelope.)

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