Fertilizing Indoor Plants
Indoor plants usually receive a lot less light than outdoor plants. Because of this, the plant is not manufacturing or using a lot of its own food, therefore if you add food it may not be used and may do more harm than good. In most cases, lightly fertilizing once or twice a year during the growing season is more than sufficient.
While fertilizers can be added to the water reservoirs of subirrigation systems, they are not required in as great a quantity or as frequently as they would otherwise be applied in a top watering system. This is because water is not leached out of the pot so quickly.
Note: The addition of a light concentration of a water soluble multi-purpose fertilizer into the reservoir once every year or two is more than adequate.
Fertilizer Types
Fertilizers for tropical plants are concentrated and contain both the macronutrients and micronutrients that meet the needs of the plants.
- Complete fertilizers are those with equal parts of the 3 main macronutrients. They generally range from 8-8-8 to 20-20-20.
- Chelated fertilizers are chemically bound to an agent that makes them non-ionized and water soluble, so that the nutrients are readily available to the plant.
- Time-release fertilizers release nutrients over a period of time of several months. Many potting mixes contain them.
A low dye, slow release balanced fertilizer is recommended for most applications. A controlled release granular fertilizer is used for atriums. There are a variety of specialty fertilizers for special situations that will be provided to you as needed. Follow these guidelines for the best results.
- Do not fertilize plants less than one year after the plant was purchased from the nursery. This is because the growing media will likely contain fertilizer residues.
- Fertilize plants in moist media so the roots do not burn. It is not sufficient to water a few minutes before fertilizing.
- Use only the recommended amounts of fertilizer.
- Palms should be fertilized in winter when new growth tips appear.
- Never fertilize diseased, stressed, or failing plants. Under these conditions we recognize that this will not reverse the situation and will probably make it worse.
- In some situations, some forms of nutrient deficiency symptoms may mimic plant illness or disease systems.
Adding Growing Medium
As a plant grows older, the growing medium (soil) becomes compacted and, depending on the composition of the soil, can become either waterlogged and unable to drain properly, or can become rock-hard and almost incapable of absorbing water. Adding fresh media can give an older plant a new lease on life. Fresh media allows a plant to be properly irrigated and allows air to circulate throughout the root system. It also contains many nutrients the plant needs which may be more effective than fertilizing.
Instead of fertilizing plants that are root bound, or those that consistently dry out between visits, it is a better practice to add growing media to the plant. This allows the plant to retain moisture properly.
Fertilizing During Growing Season
Even though plants are inside buildings, they can still detect the changes in seasons. Plants are sensitive to lengthening days, changes in air temperature and humidity levels, and the higher angle of the sun.
All plants should be fertilized when they begin to show new growth. Note when this occurs on the Fertilization Chart. The variety of plant, the level of light in which it is situated, and watering frequency will determine how often and how much to fertilize.
In the northern hemisphere, the growing season for indoor tropical plants occurs between April and September.
Fertilizing in Winter
Do not fertilize a plant when it is dormant (in fall and winter). This can damage or destroy many indoor plants.