Reusing Rockwool: When Old Cubes and Slabs Can Be Used Again
Reusing rockwool means growing a second crop in slabs or cubes from the last one. UF/IFAS Extension notes solid media can often be reused if sterilized by steaming.
The short answer
Reusing rockwool for one more crop can work. UF/IFAS notes reuse for more than one extra year is possible but not recommended, since slabs vary in water flow plus aeration. Handling damages plus compresses the structure, so discard crushed slabs. Clean plus sanitize what you reuse, then soak it before planting.
When can rockwool be reused?
UF/IFAS Extension notes solid media materials can often be reused if sterilized by steaming. It adds that research in northern states found reuse for more than one additional year possible but not recommended. The cause is variability among slabs in water conductance plus aeration.
How is old rockwool cleaned?
University of Minnesota Extension advises cleaning plus sanitizing any substrate you reuse before planting again to stop pathogen buildup. UF/IFAS lists steaming as one way to sterilize solid media.
Minnesota Extension then advises soaking any substrate in water for 24 hours plus changing the water before transplanting seedlings. University of Illinois Extension also advises wetting rockwool before planting.
| Step | Action | Source |
|---|---|---|
| Inspect | Discard crushed slabs | UF/IFAS |
| Clean | Remove old roots plus debris | Minnesota |
| Sterilize | Steam the media | UF/IFAS |
| Soak | 24 hours then change water | Minnesota |
| Limit | One extra year at most | UF/IFAS |
Source: UF/IFAS Extension, University of Minnesota Extension plus University of Illinois Extension.
When should rockwool be replaced?
UF/IFAS notes extra handling of slabs damages plus compresses the rockwool structure. A slab that has lost its shape no longer holds water plus air as it did. Replace it.
Replace slabs after one extra year of use too. UF/IFAS calls going past that possible but not recommended.
How to: step by step
- Pull out old roots plus stems.
- Inspect each slab plus discard crushed ones.
- Clean plus sanitize the slabs.
- Steam them if you can.
- Soak them for 24 hours plus change the water.
- Plant your new seedlings.
Troubleshooting
Slab drains unevenly: variability after reuse. UF/IFAS notes this is why long reuse is not recommended.
Flattened slab: damage from handling. Discard it.
Dry patches: media not wetted. Illinois advises wetting rockwool before planting.
For more on root media see hydroponic in different mediums. Read caring for your hydroponic system plus hydro setup environment for system notes. See peat moss for cannabis for another medium. Kind Seed Co also stocks cannabis seeds.
Sources
- Design suggestions and greenhouse management for vegetable production in perlite and rockwool media (EDIS), UF/IFAS Extension
- Small-scale hydroponics, University of Minnesota Extension
- Hydroponics at home, University of Illinois Extension
- Hydroponic production of edible crops: deep water culture (DWC) systems (SPES-464), Virginia Cooperative Extension
FAQ
How many times can a slab be reused?
UF/IFAS Extension notes research in northern states found reuse for more than one additional year possible but not recommended. Slabs vary in water conductance plus aeration as they age.
Can rockwool be steamed?
UF/IFAS Extension notes solid media materials can often be reused if sterilized by steaming. Steaming is the method it names for rockwool plus perlite.
Does handling hurt rockwool?
Yes. UF/IFAS Extension notes extra handling of slabs damages plus compresses the rockwool structure. Move slabs as little as you can plus discard crushed ones.
Should reused rockwool be soaked?
University of Minnesota Extension advises soaking any substrate in water for 24 hours plus changing the water before transplanting. Illinois Extension advises wetting rockwool before planting.
Does reused rockwool need cleaning?
University of Minnesota Extension advises cleaning plus sanitizing reused substrate before planting again to stop pathogen buildup.
