Time to Feed: A Beginner's Guide to Fertilizing Houseplants

For the first year of keeping houseplants, I genuinely didn't know fertilizing was a thing. I just watered them and hoped for the best. Once I started feeding them properly, the difference was almost immediate. Here's what I wish someone had told me from the start.

Why Bother?

When a plant sits in the same pot for months, it slowly uses up all the nutrients in the soil. Fresh potting mix is usually fine for the first few months, but after that, the plant is essentially running on empty. Yellowing leaves, no new growth, and small stunted leaves are often signs that your plant is hungry rather than sick.

When to Start

Most houseplants have a dormant period during winter where they slow down significantly. Fertilizing a plant that isn't actively growing is mostly a waste — and in some cases, it can actually burn the roots if the nutrients build up in the soil without being absorbed.

The general rule I follow: start fertilizing in spring when you see new growth appearing, and stop around September or October when the days shorten again. With the days getting noticeably longer now in Denmark, I've just started my feeding schedule again.

Liquid vs. Slow-Release

There are two main types you'll find in most garden centers:

• Liquid fertilizer: You dilute it in water and apply it every time you water (or every second time). It gives you more control, and the plant can use it immediately. This is what I use for most of my aroids.
• Slow-release granules: You mix them into the soil or sprinkle them on top. They release nutrients gradually over several months. Great if you don't want to think about it too much — I use these for my outdoor garden plants.

The Numbers on the Label

Every fertilizer has three numbers on it — for example, 7-3-6 or 20-20-20. These refer to the ratio of Nitrogen (N), Phosphorus (P), and Potassium (K).

• Nitrogen (N): Leaf and stem growth. Great for green, leafy plants like Monsteras and Pothos.
• Phosphorus (P): Root development and flowering.
• Potassium (K): Overall plant health and disease resistance.

For my tropical foliage plants, I just use a balanced all-purpose fertilizer. I don't overthink it. For my outdoor vegetable garden, I'll switch to something with higher phosphorus later in the season to encourage fruiting on the tomatoes and chilies.

One Golden Rule

Always water your plant before you fertilize. Applying fertilizer to dry soil can shock the roots and cause fertilizer burn — exactly the opposite of what you want. A well-watered plant will absorb the nutrients evenly and gently.

And if in doubt, use less than the recommended dose. It's much easier to add more next time than to flush out an over-fertilized pot.