Grodan Improved Gro-Block | 4in - Large - GR10 - 4in x 4in x 4in - with Hole - Strip

Step-Up Stonewool Block for Vegetative Growth, 4in GR10 Unwrapped Strip

A vegetative plant that has filled a small propagation block needs a bigger stonewool volume to keep growing into before it ever reaches a slab or full finishing container. Grodan Improved Gro-Block in the 4in Large GR10 format supplies that next-size stonewool block, built on the same engineered hydrophilic fiber technology across the GR-series and supplied with a hole ready for a rooted starter block.

This GR10 block ships in unwrapped strips, giving growers pre-connected blocks without the added shrink film for a slightly different handling and storage approach.

Key Features & Benefits

• 4in Large GR10 Format — a step-up block size for plants that have outgrown a smaller propagation cube.
• Accepts a Rooted Starter Block — the hole is sized to receive a smaller Gro-Block or plug for continued root growth.
• Hydrophilic Fiber Structure — manages water and air distribution evenly through the larger block volume.
• Multiple Packaging Formats — available loose on a pallet or in shrink-wrapped and unwrapped strip formats to match a grower's handling preference.

Who Should Use This 4in GR10 Block

Commercial growers stepping plants up from propagation into a larger stonewool volume, and who prefer to handle blocks loose from a bulk pallet, are the fit for this GR10 format.

About Grodan

Grodan pioneered stonewool growing in 1969 and today operates as part of ROCKWOOL Group, carrying that engineered fiber process through its full GR-series, including the step-up GR10 format.

Frequently Asked Questions

What stage of growth is the GR10 block meant for?

GR10 is Grodan's 4in Large format, sized for plants that have outgrown a smaller propagation block but aren't yet transplanted onto a full slab. It's a common middle step in a vegetative feeding program.

How do I transplant into a GR10 block?

Pre-soak the block with pH-adjusted water, then set the smaller rooted block or plug into the GR10's hole so roots continue growing outward. Keep the block consistently moist through this transition.

What's the difference between the loose-pallet and strip-packaged GR10 blocks?

All are the same 4in Large GR10 block and hole configuration. The difference is in packaging and handling — loose blocks ship on a bulk pallet, while strip formats come pre-connected, shrink-wrapped or not, for easier bench placement.

Can GR10 blocks go directly onto a Gro-Slab?

Yes, once roots have filled a GR10 block, it's commonly moved onto a larger slab so roots can continue growing down into the slab's volume. That move typically happens without disturbing the block itself.