Fertilizing House Plants

Never try to equate fertilizing with feeding. Plants get their energy from light, not fertilizers. Unless good light levels are supplied and the plant is growing well, fertilizing will do more harm than good. Newly purchased or repotted house plants should be given a few months rest from feeding so that they can use up the nutrients already present in their growing mix.

fertilizing plants
Fertilizing is very important for plants growing in soilless potting mixes.

Plants require three major elements for healthy growth: nitrogen (N), phosphorus (P), and potassium (K). These are always listed on fertilizer labels in the form of ratios: 6-12-4, for example, indicates 6 percent nitrogen, 12 percent phosphorus, and 4 percent potassium. Most fertilizers also contain some of the minor elements -- magnesium, boron, iron, etc. -- that plants also need for growth.

Generally speaking, fertilizers rich in nitrogen (the first number) will stimulate healthy, green growth of foliage, while those rich in phosphorus (the second number) will encourage good root development and improved flowering. Those rich in potassium (the third number) will help build up reserves for plants that have a dormant period.

A fertilizer labeled 30-20-20 would be good for leaf development and would be most recommended for foliage house plants, while flowering house plants would prefer one richer in phosphorus, such as 15-30-15. Most foliage house plants get along fine with an all-purpose or high-nitrogen fertilizer, while one with a high proportion of phosphorus is best for flowering house plants.

Constant Feed

Most plants these days are grown in soilless potting mixes that offer very little in the way of nutrients, making regular fertilizing very important. One way to make sure your house plants get the fertilizer they need is to use a constant feed method.

Simply take a liquid or water-soluble fertilizer designed for a monthly application and reduce its dosage by four. For example, if the label states it should be applied once a month at a rate of one teaspoon per gallon, apply it at every watering at a rate of ¼ teaspoon per gallon. Once a month, take the plant to the sink and leach it carefully by running clear water through its pot until the excess fertilizer runs into the drain. This helps prevent buildup.

Choosing Fertilizers for Your House Plants

Ready-to-use liquid fertilizers are convenient, but expensive, since you pay for the water they contain. Water-soluble fertilizers, available in powder or crystal forms, are just as efficient, but are more economical because you add the water yourself.

Some people prefer the practicality of slow-release fertilizers. These are available in granule form to be mixed with the soil or in spikes and tablets that are pushed into the potting mix. They need only be applied once every few months. The label on the fertilizer will suggest a recommended frequency.

Organic versus Chemical

Both organic and chemical fertilizers are available in a wide variety of concentrations. Since chemical fertilizers applied to house plants do not leach out into the outside environment, even growers who use only organic fertilizers outdoors often have no qualms about using chemical ones on their indoor plants.

One popular organic fertilizer is liquid seaweed. It is applied as a foliar spray and absorbed by the plant’s leaves.

Tools for House Plant Care

House plants do not require a shed full of expensive gardening equipment. In fact, most indoor gardeners find they can get along fine with simple kitchen utensils: a spoon for repotting, a pair of scissors for cutting off yellowing leaves, a sharp knife for taking cuttings, and a recycled window spray bottle for applying pesticides. The most important tool for proper plant care is a good watering can. Look for one with a long but narrow spout.

­In the next section, we'll talk about potting house plants.

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