When and how to apply fertilizer for your plants
The primary energy force for plants is light, but they also need nutrients that support strong growth. Here are some fertilizer guidelines and helpful tips
When should I fertilize my plants?
As a general rule, fertilize plants whenever they are actively producing new growth, which for most plants is spring to fall when light levels are high. Plants kept under lights should also be fed in winter, but feeding plants that are resting in weak winter light can do more harm than good.
Apply fertilizer when the soil is moist. Plants that have been stressed by dry soil conditions may take up more nutrients than they can use when fertilized before they have a chance to rehydrate roots, leaves, and stems.
Avoid this when fertilize your plants
Withhold fertilizer from newly purchased plants or plants that have been moved to a new place, because the task of adjusting to new conditions is difficult enough without the additional pressure to produce new growth.
How often should I fertilize my plants?
As a broad general rule, wait at least 6 weeks after repotting plants in fertilizer-enriched soil before you begin feeding them again. Plants usually need no fertilizer for several weeks after they are repotted into potting soil that includes fertilizer.
Most potting soils do include a bit of starter fertilizer, and it is best to allow plants time to make use of these nutrients before giving them additional food. Knowing when to begin feeding freshly repotted plants is part of the grower’s art because several factors influence the rate at which the plants use the fertilizer, including light, temperature, frequency of watering, size of the root mass, and overall growth rate of the plant.
Types of fertilizers
There’s are so many forms for fertilizer to choose from — liquid concentrates, powders, crystals, tablets that dissolve in water, spikes that are pushed into the potting soil, or time-release fertilizers, which are coated granules that slowly release nutrients as they dissolve.
Liquid fertilizer for plants
For most plants, the best choice is a liquid or mix-with-water powder or crystal form, which gives you tight control over how much fertilizer goes into the pot. One is no better than another, though liquids dissolve very quickly, and do not clump or melt when exposed to high humidity as powders and crystals sometimes do.
Both liquids and soluble powdered fertilizers are available as organic products, derived from natural materials, or you can use synthetic forms (plants don’t seem to be able to tell the difference). Spikes are quite unpredictable and should be used only when you anticipate a long absence when you must leave your plants in the hands of an inexperienced plant-sitter.
Slow release fertilizer
Very large, long-lived houseplants such as palms, Norfolk pines, and others that grow into small trees can easily be fed by scratching 1–2 tsp/5–10 ml of coated time-release fertilizer into the top .5 in/1.25 cm of soil.
You can also use a balanced organic fertilizer, which releases nutrients slowly as it decomposes. With either organic or time-release fertilizer, a small amount of fertilizer dissolves and moves down into the soil each time the plant is watered. Commercial growers use these products extensively, and you will often see a few round yellowish or greenish pellets on the soil’s surface of newly purchased plants. It is fine to leave these alone until you repot the plant. When you replace the soil, simply discard them along with the old potting soil in any convenient outdoor bed.