Feeding plants is one of the least of the indoor plant growers problems. So much has been learned about fertilizers, and there are so many excellent and inexpensive products on the market, the selection is mostly a matter of personal preference and convenience.
There is a wide variety of soluble fertilizers, with balanced nutrients, both organic and chemical. These mix readily with water, and are applied when the plants are watered. Or you can water with manure “tea,” made by soaking a bag of well-rotted or dehydrated manure in water, and diluting the solution until it is the color of weak tea. The elements of soluble fertilizers are quickly available for use by the plants.
For the quantity of fertilizer and frequency of application, follow the directions on the package – or feed half the recommended quantity twice as often. Half-strength solutions of packaged soluble fertilizers can also be used for foliar feeding. Sprayed on the leaves, they are ingested through the pores and provide quick nourishment.
Bone meal mixed with the potting soil will slowly release food over a long period of time. Superphosphate is used similarly, to encourage flowering. Humus, like leaf mold and manure, supplies some nourishment. Or you can mix in recommended quantities of balanced or complete commercial fertilizer; or sprinkle a small quantity on top of the soil, and scratch and water it in. These fertilizers are most desirable when the package analysis carries a note like “minor elements” or “trace elements added.” Many bagged soil mixes come with fertilizer already in the soil.
When to fertilize is more critical than how. It is a mistake to use fertilizer as a pick-me-up for plants that are resting or just “not doing very well.” Plants need supplemental feeding only when they are growing actively – perhaps preparing to flower – not when they are ailing, or resting after a period of rapid growth.
It is perfectly natural for plants to stop growing and rest at some time, or even several times during the year. Flowering vines and passion fruit plant usually stand still for a while after the blooming period ends. Tropical varieties may take life easy during the dark, cool days of winter. Bulbs and tubers shed their leaves and stems and go into a deep sleep, at intervals. Plants should not be fertilized when they are dormant or semidormant, but they willingly accept and use food when new growth shows that the growing season has begun again.
Here are the fertilizing “do’s and don’ts.” Don’t feed plants when they are weak and suffering from insects or disease, or resting or dormant, or finished flowering, or for some time after they have been potted in fresh soil, or when the soil is dry. Do fertilize when they are growing vigorously (for most, in spring and early summer), or preparing to set buds and flowers, or when the pots are filled with roots. Overfeeding at any time may mystify you by causing poor growth, sparse flowers, even slow death.