Your houseplants require both water and minerals for survival. Outdoor plants can usually pick up all the minerals they need from their surroundings without much help from the gardener. Indoor plants, however, need more attention, since nutrients in the potting soil need replenishment.

What are those three numbers on the bag of fertilizer?

Most fertilizers have the three minerals necessary for plants: Nitrogen (N), Phosphorus (P), and Potassium (K). The numbers on the bag represent the percentages of these three nutrients. A fertilizer labelled 20-10-15 has 20% nitrogen, 10% phosphorus, and 15% potassium. These are not the only elements that a plant needs, but other elements are required in much lower quantities.

How do I decide what proportions to use for my plants?

The amount of each element needed will of course depend on the species of plant. Too much is just as bad for the plant as too little, so it requires a bit of research to learn exactly what is right for your particular tropical plant. Usually this help is available by either reading the label, or by asking your plant-supply person.

What does each of the elements do for my plant?

This is a subject of continuing research by scientists. To oversimplify a bit, we can say that leafy plants need lots of nitrogen, whereas flowering varieties require more phosphorus. Potassium is useful in combating plant diseases, and is also needed by fruit-bearing plants as an aid in transporting other minerals through plant tissue.

How can I tell if my plant is getting too little or too much fertilizer?

A nutrient deficiency will often cause the leaves to lose color, or to be smaller than normal. To help the plant recover, use a soluble fertilizer, so the nutrients can be absorbed faster. Too much fertilizer can result in brown leaf tips, or in wilting. This condition is easily relieved by soaking the whole pot in water to allow the excess nutrients to be washed away.

How do I apply the fertilizer, and how often do I do it?

My method is to use a solution of dry fertilizer in water. Carefully following the directions on the package should make it easy not to over-fertilize your plants. I thoroughly water each plant, until the solution begins to flow out of the drain holes in the bottom of the pot. I find that feeding my plants about every other month is fine – more frequently for blooming plants in season.

By being careful in fertilizing houseplants, you can make sure that they not only survive, but thrive. And be sure to take advantage of your plant-supplier. He should be happy to give you advice on how to keep your tropical houseplants healthy.

Do you need more advice on tropical houseplant care? Visit the Professor’s blog on tropical houseplants, where you can find help for your plants. There are also lots of beautiful pictures, and some cool videos too.