How to fertilise your raised garden bed

A raised bed is a contained environment, so what nutrients go in is entirely up to you. The good news is that feeding a raised bed is straightforward once you understand the basics.

Start with a good base mix:

A quality premium potting mix already contains starter nutrients, usually enough for the first four to six weeks. Do not fertilise immediately after planting. Give the plants time to settle in and use what is already there.

Then build a simple routine:

1. Slow-release granules. After the first six weeks, apply a slow-release fertiliser according to the pack instructions. These break down steadily over several months, so you are not constantly topping up.
2. Liquid fertiliser during growing season. Every two to four weeks while plants are actively growing, give the bed a liquid feed. A seaweed solution or a balanced liquid fertiliser works well. This is especially important for fruiting crops like tomatoes, capsicum and zucchini, which are heavy feeders.
3. Compost top-dress. Every few months, add two to three centimetres of compost across the surface. This feeds the mix over time and improves its structure. Do not dig it in, just let it sit on top and let watering carry it down.

Signs your plants need more feeding: slow growth, pale yellow-green leaves, poor fruit set. Signs of too much: lush leafy growth but no fruit, or brown burnt leaf tips. For more on that, see our guide to overfertilising.

What to avoid: heavy doses of high-nitrogen fertilisers push leafy growth at the expense of fruit and flowers. Go steady and consistent rather than large doses occasionally. And avoid fertilising during a heatwave or when plants are stressed, as they cannot absorb it well.

Refreshing older beds: after a few seasons, premium potting mix loses some of its structure and nutrients. Top it up with fresh mix and compost each year to keep the bed performing well.

For more on filling your bed from scratch, see our filling guide.

What should I plant right now? Our free planting calendar shows what suits your postcode this month. Ready to grow? Browse our raised garden beds or build your own with the garden bed builder.

Image: Daderot, CC0, via Wikimedia Commons.