Generally the plant you buy already potted, should be able to get along without extra nutrients for at least a month or so. If it fails to prosper, showing signs of distress (lackluster and curling leaves, prematurely falling flowers, etc.) before that time, it is probable that the difficulty lies not in the lack of food, but in the plant itself, or in the environment you have provided. If after a month the plant continues unthrifty, then by all means try feeding it. Remember, when you use a plant food, that the method outlined in the instructions on the package have been developed as the result of long experience. Follow them exactly. It is a natural tendency to feel that if one tablespoon will be beneficial, then two will be twice as effective. Don’t let yourself make this mistake. Excessive feedings of plant food may easily burn the roots and kill the plant.
While we must be careful not to overfeed, we must also realize that plant food is a necessity, and should be fed at intervals in the proper amounts to all plants, especially those that must remain pot bound over a long period of time. One way to ascertain whether a plant is in need of feeding is to look at the roots. To do this you hold the plant upside down with one hand covering the earth, and with the plant stem between the second and third fingers. With the other hand you lift the pot. You may have to give it a couple of taps with a mallet to loosen the earth from the inside. Inspect the ball of earth, and if the roots are thick, completely encasing the earth ball, then the plant should have regular feedings. If the ball looks as though it is entirely made up of roots, with little or no earth showing, then it is time to repot. (See the discussion of potting and repotting in Chapter 6.) Another point to remember is that flowering plants usually need more food than foliage plants.
In your supply store you will find commercially packaged foods which are effective for almost every variety of house plant. There are a few plants such as Roses and African Violets whose makeup is such that they need special foods. These too are readily available, and should be used instead of the general purpose foods.