Houseplant fertilizers are full of the same macronutrients that are found in any fertilizer: N (nitrogen), P (phosphorous), and K (potassium). Nitrogen is important for all plants and healthy leaf growth in particular. Phosphorous is crucial for healthy root systems that are able to transfer energy and nutrients throughout the plant. Potassium also helps the transfer or energy and nutrients throughout the plant, but this nutrient plays a more central role in regulating photosynthesis. Commonly, houseplant fertilizers have other nutrients in smaller quantities. These nutrients include calcium, magnesium, iron, zinc, sulfur, manganese, nickel, boron, and copper. Along with finding the perfect type of houseplant, the following resource guide should help determine what fertilizers and soil amendments you may want to use for your houseplants.
Do You Need to Use Houseplant Fertilizers and Soil Amendments?
There are many plants that require minimal, if any, fertilizers, food, insecticides, or other soil treatments. One of the core components of easy-care houseplants is that they rarely require these types of soil amendments under most indoor conditions. Moreover, plants that grow more slowly, are placed in low-light conditions, or have been repotted recently are unlikely to need fertilizer. Other houseplants require timely fertilizers and/or carefully controlled soil conditions to thrive indoors and show off their best foliage and flowers. Many types of houseplants can be grown in water but need fertilizer additives as part of their watering schedule.
That said, if the soil becomes too acidic or alkaline, if the plant wasn’t potted with the best soil, if the plant keeps suffering from root rot, or if the plant is struggling to produce flowers, almost any type of houseplant can benefit from some type of fertilizer or soil amendment. Testing the soil quality is often necessary to know what type of soil treatment is best for your plant. For choosing the best fertilizer product, you may want a soil testing kit that includes N-P-K soil analysis. The most popular testing kits and mail-in soil testing services include Luster Leaf/Rapitest®, Soil Savvy, and AccuGrow.
For choosing aerators and pH soil amendments, other soil testing kits are available that focus on measuring the moisture level and pH. The most popular products include Sonkir, Atree, and other manufacturers of 3-in-1 soil testing meters.
How and When to Use Fertilizers
There are an endless number of personal philosophies for fertilizer products and applications, but there are also a handful of basic principles that will help guide your initial plan for houseplant fertilizers. First, you should only fertilize plants when they’re ready to grow and actively extract nutrients from the soil. For most every houseplant, this means the spring and early summer. How often you should apply the fertilizer really depends on the type of product. Liquid and powder fertilizers may be used as frequently as every other week. Granular fertilizers should be applied every month or two. Slow-release fertilizers should last the entire growing season but are known for being more prone to causing issues with over-fertilization.
The other golden rule of fertilizing houseplants is to always err on the side of using too little fertilizer. Some houseplants do not need fertilizers at all, and most houseplants can make do with even a minimal amount of added nutrients. In contrast, over-fertilization can cause severe, irreparable damage to houseplants as roots are exposed to corrosive minerals. Many people dilute soil fertilizers for their houseplants even more than the manufacturer recommendations. Unless you know the soil has a nutrient deficiency, we recommend using only half of the recommended amount of fertilizer.
Buy, Choose, or Make Your Own Houseplant Fertilizers
The best results will come from soil testing, but many people successfully manage their houseplants simply by following a few basic rules of thumb. We first recommend making sure your plants have the best soil for each type of houseplant. This will reduce the amount of fertilizer and other amendments the soil will eventually need.
We also recommend considering how often you like to tend to your houseplants. This will determine whether you’re better off with a liquid/powder fertilizer or a granular product. When in doubt, go with the liquid/powder form. Houseplants are unlikely to experience significant harm if you miss one or two fertilizer applications.
Along with knowing which houseplants are fast-growing, you should know the type of growth for that houseplant. Green foliage plants often do best with balanced or nitrogen-heavy fertilizer products. Flowering plants may do better with fertilizers that have higher concentrations of phosphorous. Apart from fertilizers with exact N-P-K ratios, there are many types of holistic fertilizers and soil amendments you can make at home. Along with general composting, some of the most common household ingredients used for homemade fertilizers include eggshells, coffee grounds, aquarium water, and Epsom salt.
Soil Amendments for Houseplants
Other than encouraging new growth with fertilizers, the most common reasons to add soil amendments is to improve drainage, increase water retention, aerate the soil, and/or balance the pH of soil that’s become too acidic or too alkaline. Peat moss, perlite and vermiculite can aerate the soil and regulate moisture levels. Simply adding gravel or sand can improve drainage. Adding a tiny amount of vinegar to your watering can may be helpful if you have very hard, alkaline tap water.
There is also an endless list of organic amendments that can be used for specific purposes or as a general homemade fertilizer. Compost, for example, is a better choice for houseplants that can benefit from added nutrients as well as slightly alkaline soil. Popular organic materials that are used as soil amendments include peat moss, wood chips, bark, sawdust, lime, ammonium sulfate, gypsum, straw, compost, manure, or other biosolids. Learn even more about choosing different types of soil amendments.
Houseplant Fertilizers and Care Practices
Fertilizers and soil amendments are no substitute for general houseplant care that provides the right amount of watering, soil moisture, and light exposure. Fertilizers and soil amendments are not a cure-all for houseplants. If your plant is struggling, it’s important to identify other potential problems and solutions before adding a bunch of fertilizer and assuming that will fix the problem.
Fast-growing plants are the ones that have the greatest need for soil fertilizers, but repotting plants that have outgrown their current pot is another way to replenish the soil. Fresh potting soil is chock full of essential plant nutrients, and this is another reason why some houseplants may never need soil amendments. Adding fertilizer along with new soil may cause over-fertilization.