4" Rockwool Block Cover, pack of 40

A Dual-Sided Light-Reflecting Cover for Rockwool Blocks, 4in

An exposed rockwool block lets light reach both the growing media and the space around the plant's base, and that light exposure is what lets algae and mildew take hold on a damp block over the course of a grow cycle. This Hydrofarm 4 inch block cover addresses that with a dual-sided design: one side reflects light back up toward the plant's leaves, while the other blocks light from reaching the rockwool block itself.

Sized for a 4 inch rockwool block and sold in a pack of 40, this cover works well with GRODAN blocks and similar rockwool cube and block products.

Key Features & Benefits

• Dual-sided design — reflects light to plant leaves on one side while blocking light from growing media on the other
• Reduces algae and mildew growth — limits light exposure to the damp rockwool block, a key factor in algae and mildew development
• Sized for 4 inch rockwool blocks — works well with GRODAN blocks and similar rockwool products
• Pack of 40 — for growers outfitting a full bench or hydroponic run at once

Who Should Use This Block Cover

Growers running 4 inch rockwool blocks, including GRODAN blocks, who want to limit algae and mildew growth on exposed media will benefit from this dual-sided cover.

About Hydrofarm

Hydrofarm has manufactured cultivation equipment since 1977, when founder Stuart Dvorin started the company as Applied Hydroponics; the company has operated out of Petaluma, California, since 1994, supplying growing containers, propagation hardware, and hydroponic equipment to commercial and home growers.

Frequently Asked Questions

What size block does this cover fit?

This listing is for the 4 inch rockwool block cover, sized to fit a 4 inch rockwool block. It works well with GRODAN blocks and similar rockwool products.

How many covers come in this pack?

This listing ships in a pack of 40 covers. That count is sized for outfitting a full bench or hydroponic run at once.

How does this cover reduce algae and mildew?

The cover blocks light from reaching the growing media side of the rockwool block, and light exposure combined with the block's moisture is what lets algae and mildew take hold in the first place. Cutting off that light exposure limits the conditions those organisms need to establish.

What does dual-sided mean for this cover?

One side of the cover reflects light back up toward the plant's leaves, while the other side faces down to block light from the growing media. This gives the cover two functions in one piece rather than needing a separate reflective layer and light-blocking layer.

How do I install this cover on a rockwool block?

Fit the cover over the top of the rockwool block so the reflective side faces up toward the canopy and the block itself is shielded from light. Cut or fold the cover as needed to accommodate the plant stem at the block's planting hole.