Tips for applying liquid fertilizer

Liquid fertilizer is a great way to provide nutrition for your bonsai. I’ve been using fish-based fertilizers for years and although it’s smelly, it’s effective and offers control when I want to limit how much fertilizer each tree gets.

Fish emulsion

While it’s easy to dilute concentrated fertilizer and apply it to your bonsai, there are three things you can do to fertilize more effectively.

1. Lightly water before applying fertilizer
2. Stop fertilizing before fertilizer begins to run out of the drainage holes
3. Lightly water after applying liquid fertilizer

The most common reason offered for watering before fertilizing is to prevent fertilizer burn. I actually haven’t seen much fertilizer burn caused by fertilizing dry trees, but there is still good reason to water lightly first.

You may have noticed that the water doesn’t always soak into the soil evenly. Some areas of the rootball may need several passes before they get wet (see “Summer watering tip” for details). If you pour liquid fertilizer directly onto dry soil, the fertilizer may not reach all of the rootball before it begins to drain out of the pot. By watering lightly first, the water can wet the soil which will help the fertilizer soak in evenly.

Watering before fertilizing

Once the soil is wet, it’s time to apply the fertilizer. The idea behind the second tip to stop fertilizing before the fertilizer runs out of the pot is to avoid wasting fertilizer.

Applying fertilizer

Foliar fertilizing, by the way, works, and is a great option for trees with few or weak roots.

Foliar fertilizing

The third tip is to lightly water after applying fertilizer. The main benefit of doing this is to wash excess fertilizer away from foliage and from the lip of the pot.

Chemical fertilizers may not leave much of a trace after application, but organics like fish-based fertilizers do, especially if additional nutrients like iron are added to the mix.

Fertilizer residue on holly leaves

Fertilizer residue on the pot

Watering after fertilizing may also cut down on the smell when using pungent fertilizers like fish emulsion.

A single pass with the hose to water in the fertilizer

For general information about fertilizing bonsai, see “How to fertilize bonsai,” part of the Beginner Series of articles designed to get new enthusiasts up to speed quickly.