Can You Reuse Rockwool? 7 Ways to Repurpose Used Cubes

August 22, 2013

📚 Part of the Living Towers Seeds & Seedlings Guide
This guide is one of our collection of articles designed to help you choose crops, start seeds successfully and grow strong, healthy seedlings.

← Return to the Seeds & Seedlings Guide

If you've finished a crop or have a rockwool cube where a seed didn't germinate, you may be wondering: can you reuse rockwool cubes?

Used rockwool doesn't necessarily have to go straight into the trash. Depending on its condition, it may be possible to clean and reuse it, or you can repurpose it for other gardening projects.

Can Rockwool Be Reused?

Yes, rockwool can sometimes be reused, particularly when a seed failed to germinate or the cube has had very little root growth. Before using it again for growing, old roots and plant material should be removed and the rockwool should be cleaned.

Heavily rooted or damaged cubes can be difficult to reuse for another seedling. Instead of using those cubes again for seed starting, consider repurposing the rockwool elsewhere in your garden.

Seedlings growing in rockwool cubes before being transplanted into a Tower Garden

Jump to a Section

Learn how to reuse, clean or repurpose your used rockwool cubes.

Can You Reuse Rockwool? Ways to Repurpose Rockwool How to Clean Rockwool for Reuse Where to Buy Rockwool

When Can You Reuse a Rockwool Cube?

Rockwool is easiest to reuse when it is still relatively clean and intact. For example, if you planted a seed that never germinated, the cube may have little or no root material in it and can be a good candidate for reuse.

Rockwool that has supported a mature plant is more difficult to reuse as a seed-starting cube because roots grow throughout the fibers. Removing those roots can damage the structure of the cube.

If a cube is heavily rooted, falling apart or otherwise difficult to clean, repurposing it is usually more practical than trying to use it again for a new seedling.

4 Ways to Repurpose Used Rockwool

Even when a rockwool cube is no longer suitable for starting another plant, there are still several ways you can put it to use.

1. Improve Soil Structure

Cut used rockwool into smaller pieces and mix it into garden soil or potting mixes. Its fibrous structure can help create additional air space within the growing medium.

2. Add It to Compost

Break used rockwool into smaller pieces before adding it to your compost. The pieces can help create air spaces throughout the compost mixture.

3. Reuse It in Planters

Small pieces of used rockwool can be incorporated into planters as part of the growing medium rather than throwing the cubes away.

4. Use It as Part of a Growing Medium

Clean rockwool can be incorporated into other growing media for container plants. Remember that rockwool itself does not provide the nutrients plants need, so plants will still need appropriate nutrition.

How to Clean Rockwool for Reuse

If a seed didn't germinate or a cube has only minimal root growth, you may choose to clean the rockwool before using it again. Remove as much old root and plant material as possible first.

1. Hydrogen Peroxide Method

Remove as much old plant and root material as possible.
Mix 1 part hydrogen peroxide with 8 parts water.
Submerge the rockwool in the solution for 24 hours.
Allow the cube to drain before preparing it for planting again.

2. Baking Method

Remove as much old plant and root material as possible.
Preheat your oven to 250°F.
Place the rockwool cubes on a baking sheet.
Heat until the inside of the rockwool reaches 180°F and maintain that temperature for 30 minutes.
Allow the cubes to cool completely before reuse.