Sure, many indoor plants can survive with sunlight, water, and love, but if you want houseplants to truly thrive, you’re going to need to learn some indoor plant fertilizing basics. Fertilizing and feeding indoor plants is vital because as you water them nutrients are washed away from the soil over time. In order to keep indoor plants happy and healthy, those nutrients need to be replenished—and that’s what fertilizer is for!
If you’re daunted by the details of fertilizing and feeding indoor plants, you’re absolutely not alone. You could easily spend days researching fertilizer and still be confused—but that’s why we’re here. At Tonic Living and Plantscapes, we pride ourselves on demystifying the ins and outs of indoor plant maintenance, whether you have us curate and care for your indoor plantscape or choose to DIY your home greenery. Here’s a rundown of Indoor Plant fertilizing basics to help your houseplants live their best life.
Indoor Plant Fertilizing 101
With indoor plant fertilizer, it all comes down to the N-P-K ratio. N for Nitrogen, P for Phosphorus & K for Potassium. These life-giving elements are the key Macronutrients your plant needs. A complete fertilizer also contains Micronutrients, like calcium, magnesium, sulfur, and several others.
Organic fertilizers usually come from plant waste (compost), animal waste (manure), or powdered minerals like bone meal.
General/all-purpose indoor fertilizers will work for most of your leafy houseplants, but flowering plants like orchids, african violets, and jasmine need a fertilizer higher in phosphorus. Cactus and succulents tend to prefer a fertilizer with less nitrogen.
The 411 on NPK
Nitrogen for healthy foliage growth
Plants take in lots of nitrogen. It allows them to absorb energy from sunlight—the process of photosynthesis—which encourages the production of protein that becomes plant tissue. Nitrogen is an essential nutrient for leafy growth. More leaves = more sun absorption = bigger, stronger, and more vibrant plants!
Phosphorus for healthier roots, flowers, and fruits
Phosphorus helps indoor plants produce, store, and move energy from the roots to the leaves and flowers. It promotes a strong root system, healthier fruits, and vibrant flowers, plus a longer bloom time.
Potassium (K) for overall health and resilience
Although plant’s don’t naturally produce any potassium, their overall health, growth, and longevity rely on it (nature is often tricky like that, isn’t it?). Potassium builds a strong disease resistance and stress response, plus it regulates water and CO2 intake.
Main Types of Indoor Plant Fertilizer
Liquid — Use every to every-other watering
Liquid fertilizer typically comes in a concentrated form, which means you’ll dilute it in water and incorporate it into your normal watering routine. This method makes it really easy to remember and is our choice for beginners! With liquid fertilizer, you get complete control over how much or little you feed your plants, plus an even distribution of food in the soil.
Spike or Tablet — Use monthly to bi-monthly
Just like the name suggests, this fertilizer comes in a spike or tablet form that gets pressed into the soil. Fertilizer spikes and tablets dissolve over time, making them a super low-maintenance option for indoor plant fertilizing. All you have to do is replenish them once a month. We like spike fertilizers because they aren’t messy and there is no risk of smell (which can be an issue with the liquid method). The spike or tablet fertilizer is activated by water, so as long as you are keeping your plants hydrated you won’t have to worry about it! The downside? You get less control over how much food your plants are getting and it’s not as evenly distributed. This means the roots may stretch out and get tangled looking for nutrients.
Slow-Release or Granular – Use once or twice during growing season
This method is really great for people who are really busy or forgetful… All you have to do is sprinkle the granules on the soil once each growing season. The liquid nutrients are encapsulated in a coating which breaks down slowly, releasing the fertilizer in low doses over a long period of time. It’s the easiest way to fertilize—but we don’t recommend it because it’s usually a synthetic/chemical-based formula.
Things to Consider When Fertilizing Indoor Plants
You only need to fertilize plants when they are actively growing. For most indoor plants, that means spring and summer. (If you live in a tropical climate, you can fertilize year round.)
Start fertilizing 4-8 weeks before the last frost, and stop fertilizing 4-8 weeks before the first frost.
Overwhelming a plant with nutrients can do more harm than good, so start slow on the first few doses, and dilute your fertilizer up to 2 times more than the directions recommend in the spring. Too much fertilizer can burn the plant’s leaves, reduce the ability for plant roots to uptake nutrients, or even kill the plant (yikes!).
Just like in the spring, your autumn fertilizing should taper down in intensity. Before the first frost (and before your plants go dormant) you can double-dilute your fertilizer again for the last few applications before you stop completely.
If your plant has been recently repotted, you can skip fertilizing for a handful of waterings. If you are planning to repot your plant, feel free to fertilize up until the repotting.
If the soil is bone dry, water it liberally the day before fertilizing.
If your plant is showing signs of stress, hold off on fertilizing until it looks a little happier.
Low-light plants, cactus, and succulents have adapted to live in low-nutrient soil and can go years without being fertilized. However, it doesn’t hurt to give them a low dose or two at the beginning of the growing season!
If you have any questions about fertilizing indoor plants, feel free to reach out to us! We love helping new plant parents (or seasoned indoor gardeners) troubleshoot tricky situations and grow their green-thumb confidence.
