How to Feed Your Houseplant
Outdoor plants are relatively self-regulating. They get most of what they need from the surrounding air and soil and often require no feeding aid. Indoor plants are much more reliant on the gardener’s tender ministrations. But it’s possible to overdo it.
General fertilizers have varying concentrations of Nitrogen (N), Phosphorus (P) and Potassium (K) or potash, hence the shortened name: NPK. The letters are the elements’ chemical symbols. 10-10-10 is common but other variations exist, such as 10-20-10 or 5-2-7. The numbers indicate the relative amounts of each element in the fertilizer.
Since every plant species has, as the name suggests, specific needs it’s important to research which need what type and when. Some plants, such as flowering or fruit species, tend to require more in the early Spring, but go dormant in the late Fall. Adding the same amount of fertilizer later in the year for these types can poison the plant, since it can’t process the excess. Often, zero is the appropriate amount.
Each plant takes up fertilizer at a different rate as well. Slow-release nitrogen, in the form of beads is often desirable, where it helps produce green foliage. Since nitrogen often comes in the form of a salt, such as urea, it will readily absorb moisture from the surrounding soil. Beads take longer to deliver material below the surface.
Phosphorus supports the ability of flowering plants to bloom, and is influenced by the pH level of soil. pH is a numeric measure of acidity, on a scale from 0 to 14, with pure water being 7 - neutral. Measures closer to 0 are more acidic, those closer to 14 more basic.
Soil that is either too alkaline (basic, the opposite of acidic) or too acidic can inhibit the plant’s absorption or release of phosphorus. Phosphorus is particularly important for healthy root growth.
Potassium helps fight disease, but promotes fruit development in fruiting species as well. Since it’s chemically active in the presence of oxygen and water, it helps transport elements through the tissues of the plant.
All purpose liquids are convenient and will work with a wide range of plants, but for some they deliver fertilizer too quickly. They do have the advantage of delivering fertilizer very evenly, however.
Whichever proportion and form you choose, be sure not to apply fertilizer to a dry soil. That results in a very heavy concentration of elements and can easily burn the plant.
Most plants that you have just purchased will not need fertilizer right away, if they’ve been properly cared for at the nursery or gardening center. Flowering plants will need a little more, a little sooner in Spring and cacti need almost none, ever. You can tell if you’ve overdone it by looking for stunted growth, wilting or dried tips assuming you’ve watered properly.
To flush excess fertilizer just apply a little extra water to a pot that has good drainage. Repeat the procedure three or four times at one hour intervals.