What kind of fertilizer to use? For convenience sake, most prefer to use one of the many kinds of fertilizer products designed specifically for houseplants. These come in several different analyses, with the most common types having a 1:1:1 ratio of nitrogen to phosphate to potassium. A commonly available analysis is one containing 20-20-20. Some products are still seen with the 1:2:1 ratio, with analyses such as 15:30:15 being fairly common. Most current data suggests that the extra phosphorus is not needed and may actually encourage stem stretching and weak growth. Some of these products are supplemented with trace minerals, which can be important if a plant is grown long term in a completely artificial potting mix. If some soil has been added to the potting mix, the presence of trace minerals is not important.
The easiest to use houseplant fertilizer products are the highly soluble fertilizer salts that are dissolved in water. These are convenient, easy to use and give good results, provided they are applied according to recommendations. Most manufacturers recommend fertilizing once every two weeks, but monthly feeding is usually adequate. In the wintertime, fertilization should be curtailed.
Several types of slow-release fertilizer products are available for houseplants as well as various kinds of slowly available organic fertilizers. These
products provide the convenience of continual feeding for three or four months without the hassle of measuring and mixing. However, they tend to produce less dramatic results than liquid fertilization. A good strategy might be to use the watersoluble fertilizer during the brighter days of summer and the slow-release products during the darker days of winter.