Decoding Houseplant Fertilizer: What, When, & How Much

It may seem like fertilizing your houseplants is too complicated, so it’s just easier to skip it. However, fertilizer is the only way for houseplants to get the nutrients they need in their small, controlled environments. Since houseplants are kept in pots, soil nutrients don’t get replenished in the soil the way it does outdoors. By leaving fertilizing out of your houseplant maintenance routine, you may be missing out on the true potential of your favorite plants!

As we head into spring in Iowa, it’s the perfect time to start thinking about giving your houseplants a boost as they begin to come out of their winter rest period.

What is in Fertilizer?

Fertilizer is most commonly a mix of nitrogen (N), phosphorus (P), and potassium (K). The amounts of each of these nutrients are called the NPK ratio. They’re commonly seen on fertilizer packaging as numeric ratios, like 10-10-10, or 6-12-4. Most fertilizers also include trace amounts of other minerals and nutrients that your plants need. Most houseplants do best with a balanced (i.e., 10-10-10 or 20-20-20) fertilizer specifically designed for houseplants, or a formula with a higher nitrogen number. But, houseplants that flower need a fertilizer with a higher phosphorus number to support blooming. Some of the more finicky bloomers, like African Violets, have specific fertilizers formulated just for them. Higher nitrogen promotes more greenery and lush leaves, high phosphorus promotes more blooms.

What Type of Fertilizer is Best?

There are so many fertilizer options available, it can be hard to decide on the right one. We recommend two guidelines when choosing fertilizer:

1. Make sure it says on the packaging that it’s specifically for houseplants.
2. Consider an organic brand if possible.

The reason for these guidelines is that fertilizer for outdoor plants or lawns has different ratios of nutrients and minerals because indoor and outdoor plants have different nutrient needs. 

We recommend organic fertilizers because they’re healthier for your plant’s soil, and our planet, in the long term. Organic fertilizers are created from organic compounds in things like seaweed, compost, or worm castings. Synthetic fertilizers are often created from inorganic compounds that are a byproduct of the petroleum industry. These products deliver nutrients, but that’s where the benefits end. Organic products give your plants and soil a boost by adding organic matter that helps to repair nutrient-depleted soil, along with beneficial microbes that contribute to healthier soil over time. 

If you do prefer synthetic fertilizers, we recommend Scott’s Osmocote for houseplants. It comes in a pellet form that dissolves slowly, and you only need to use more every four months. It makes fertilizing houseplants super quick and simple. 

The organic fertilizer line we recommend is Espoma. Espoma’s products are of excellent quality, and they have a variety of different organic fertilizer options, including easy-to-use liquid formulas. 

How to Fertilize Your Houseplants

Here are a few essential tips to remember when you fertilize your houseplants.

• Only fertilize during the growing season (once you start seeing signs of new growth, or in mid-March), avoid fertilizing your houseplants in winter.
• Be conservative in the spring and fall and dilute the fertilizer to half the recommended strength.
• Taper off fertilizer applications. Starting in mid-August, diluting to half-strength again, and fertilizing less frequently.
• Liquid fertilizers should usually be applied every 2 weeks. Always water plants with plain water before applying liquid fertilizer.
• Granular fertilizers are usually applied once a month.
• Slow-release fertilizers are usually applied once every 4 months.
• Some fertilizers can be applied as a spray to the leaves, check the bottle for instructions.

We don’t recommend fertilizing succulents and cacti. It can be tricky to make sure they get the right amount, and too much fertilizer might kill them!

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Fertilizing your houseplants is pretty simple, and it’s not something to avoid. Your houseplants will thank you for feeding them with healthy, vigorous growth during their growing season! If you’ve got any questions at all, stop by our garden center and ask our expert staff. We can help you figure out which product is best for you and explain how to use it.