Indoor Plant Fertilizer and Feeding How-Tos
Authored by Leah Chester-Davis
Oh, the joys of indoor plants! They bring a bit of nature inside and supply lovely accents to our homes. A space comes alive when a pretty houseplant graces it. All it takes is a little attention and the right spot, and houseplants will thrive.
Providing houseplants with the nutrients they need is one part to good care. Other needs are proper lighting and humidity levels. Houseplants typically do not need a lot of fertilizer but it’s helpful to follow a basic guide.
When to feed your indoor plants
The growing season for most plants is from spring to fall, and that is the time that fertilizer is most useful to them. Fertilize houseplants from March through September. In late fall and winter months, due to less light and cooler temperatures, plants slow their growth. This is the time to cease any fertilizer applications.
What kind of fertilizer to use
Fertilizer is available in many different forms – liquid, granular, pellets, tablets, or spikes – and it can be confusing to know what is best to use. Fertilizer packaging lists three numbers. For example, a balanced fertilizer such as 8-8-8 contains nitrogen (N), phosphorus (P), and potassium (K) in equal amounts.
These three are known as macronutrients and each has a purpose. Nitrogen promotes green, leafy growth. Phosphorus encourages flowering and root growth. Potassium strengthens stem growth and stress tolerance. For example, fertilizers formulated for blooming plants typically have more phosphorous (P) than the other two macronutrients. If you have primarily foliage plants, consider a fertilizer higher in nitrogen (N).
In addition to the macronutrients, several nutrients may be included in much smaller quantities such as calcium, magnesium, and sulfur. Trace elements include boron, copper, chlorine, iron, manganese, molybdenum, and zinc.
Types of fertilizer
Slow release
When a fertilizer is labeled “slow release,” that means it is in a pellet, spike, or tablet form which will release nutrients over a period of 3 to 6 months. Slow-release pellets can be mixed into the soil at the time you are planting or transplanting, or they can be spread around the surface of the container. Follow label directions.
Granular
Granular forms of fertilizer can be sprinkled on top of the soil and then lightly mixed or watered in. Follow label directions and consider your plant and container size to avoid overfertilization. Granular typically lasts around 6 weeks (about 1 and a half months).
Liquid
Liquid fertilizers in liquid or powder form require being mixed with water to dilute to the right strength that is best for plants. This form is readily available to plants. Follow label directions and measure accordingly.
Indoor plant fertilizer
Fertilizers specifically formulated for indoor plants are available and help take any guesswork out of how much to apply when you follow label directions. Most hold micronutrients that can be deficient in many houseplants. Some products get even more specialized, such as options for cactus and succulents; orchids; and African violets.
The University of Connecticut Soil Nutrient Analysis Laboratory recommends selecting a fertilizer based on how frequently applications are needed for your plant. Use a water-soluble powder or liquid concentrate if plants need to be fertilized on a weekly, biweekly, or monthly basis. If long intervals between fertilizer applications are needed, select a slow-release fertilizer. In most cases, an all-purpose, balanced fertilizer can be used.
Leaching soil
With any type of fertilizer, it’s best to start with a light application, or half strength of what is recommended on the label, until you are more in tune with your plants’ needs. Fertilizers have salts that can build up in the soil over time. In fertilizer's case, it may be true that less is more. Too much fertilizer can result in plants becoming leggy and overgrown. It can be harmful to plants and burn roots and leaf margins. If roots and leaf tips are brown, and the leaves are poorly shaped or wilting, those are clues of overfertilization. Too much fertilizer prevents plants from adequately taking up water. Another clue is a white crust on the outside of clay or terracotta pots or around the pot rims.
For instances where salt has been built up over time, or when fertilizer has been applied too heavily, New Hampshire Extension recommends leaching the fertilizer out of the soil by watering plants with a lot of fresh water until it drains freely from the bottom of the pot. Always empty the saucer so water doesn’t remain standing for long. Another solution, according to Connecticut’s Soil Nutrient Analysis Laboratory is to repot the plant, removing as much of the old potting mix as possible, and replacing it with fresh medium.
Organic or synthetic plant food
Organic and synthetic or chemical options are available. The organic options contain natural substances such as fish emulsion or seaweed extract. Check the label for information on whether the product is organic or synthetic, and what trace elements it contains.
How to know indoor plants need fertilizer
Pale foliage or stunted growth are signs that your plants may be struggling and need some nutrients. Give them a shot of fertilizer and make sure they are receiving adequate lighting requirements.
Be a plant sleuth
With these tips on the effects that too much or too little fertilizer can have on indoor plants, along with information on other requirements such as proper lighting, humidity levels, and basic indoor plant care, you will be better equipped to diagnose problems and implement solutions to keep your indoor plants happy and thriving.
