Description
The Grodan Gro-Block Improved GR10 4" with hole is the current-generation 4 inch rockwool block. 4 x 4 x 3.1 inches, shrink-wrapped in strips, with a pre-formed hole for a propagation cube.
UK and EU stock.
What "Improved" actually changes
Grodan worked with Wageningen University in the Netherlands and with commercial growers in North America to re-engineer the wool structure and the wetting agent. Three things come out of it that you can feel in the room:
- Faster rooting-in – the optimised fibre structure lets roots take hold sooner after transplant.
- Even water and EC through the whole block – not just across the block but over its height, which is what makes crop steering predictable rather than a guess.
- Holds its shape – structure, firmness and rigidity stay put across the cycle instead of slumping once it has been saturated and dried a few times.
The advanced wetting agent and hydrophilic treatment are the reason it re-saturates so evenly, which in turn means less water and less nutrient wasted getting the block back to where you want it.
Wetting instructions
The Improved blocks have their own preparation procedure, which is not the same as the 24 hour soak used on standard rockwool. Grodan's wetting instructions for Improved Gro-Blocks (PDF). Follow those rather than the generic advice.
Improved GR10 or the standard 4 inch block?
| Improved GR10 4" (this product) | Standard Grodan 4" Block | |
|---|---|---|
| Size | 4 x 4 x 3.1" | 10cm |
| Hole | Pre-formed, one size | Choose 2.5cm or 3.6cm |
| Wetting agent | Grodan Advanced | Standard |
| Preparation | Follow Grodan's Improved wetting PDF | 24 hour soak at pH 5.5 |
| Best for | Crop steering, tight EC control | Straightforward veg, hole choice |
Which rockwool size do I need?
Rockwool works as a ladder. You start small and pot on into the next size up, each time without disturbing the roots. Here is the full range we stock and where each one sits.
| Product | Size | Where it fits | Takes |
|---|---|---|---|
| Grodan Propagation Cubes | 25mm or 36mm | Seed and cutting | Bare cutting or seed |
| Cultiwool Loose Mini Cubes | 10mm, 90L or 200L | Loose fill, any pot | Fills pots and trays |
| Cultiwool Mapito | 80L bag | Loose fill, any pot | Fills pots and trays |
| Grodan Block 3" | 7.5cm | First pot-on | 2.5cm or 3.6cm hole |
| Grodan Improved GR4 3" | 3 x 3 x 2.5" | First pot-on | Pre-formed hole |
| Grodan Block 4" | 10cm | Veg | 2.5cm or 3.6cm hole |
| Grodan Improved GR10 4" (this product) | 4 x 4 x 3.1" | Veg | Pre-formed hole |
| Grodan 6" Hugo Block | 150 x 150 x 140mm | Veg to harvest | 36mm hole |
| Grodan 6" Hugo, dripper hole | 150 x 150 x 140mm | Veg to harvest | 36mm hole plus dripper hole |
| Grodan Improved Hugo 6" | 6 x 6 x 5.8" | Veg to harvest | Pre-formed hole |
| Cultiwool 8" Big Daddy Block | 20 x 20 x 19.5cm | Full cycle, large plants | Takes an 8" cap |
| Cultiwool 25cm X-Fibre Mini Slab | 25.2 x 19.5 x 7.5cm | Under a block, full cycle | One 6" or 8" block sits on top |
| Grodan Vital Slab 1m | 100 x 15 x 7.5cm | Multi-plant, full cycle | Three to four blocks |
| Grodan Vital Slab 1.3m | 130 x 15 x 7.5cm | Multi-plant, full cycle | Four to five blocks |
Sizes are nominal. Blocks are sold as singles or in strips depending on the line.
Goes well with
- Grodan Improved GR4 3" – The rung below in the same Improved range.
- Grodan Improved Hugo 6" – The next size up, and where most growers finish.
- FloraFlex 4" Flora Cap v2.0 – Sits on a 4" block to spread feed evenly and block light, which keeps algae off the wool.
- Grodan Propagation Cubes – What goes in the hole.
Frequently asked questions
Do I prepare these the same as normal rockwool?
No. The Improved range has its own wetting procedure because of the advanced wetting agent. Use Grodan's Improved Gro-Block instructions, not the generic 24 hour soak.
What does GR10 mean?
It is Grodan's range code for the medium Improved block, the 4 inch. GR4 is the 3 inch version. The number is a Grodan code, not the size in centimetres.
Is it worth paying more than the standard block?
If you are crop steering and watching EC and water content closely, yes, because the even distribution through the block is what you are paying for. If you are simply growing on to transplant size, the standard 4" block does that job and lets you pick your hole size.
What feed should I run?
pH 5.5 to 5.8, EC stepped up as veg takes off, aiming for 10 to 30 percent run-off per feed. See Base Nutrients, pH & EC Meters and Dripper Systems.
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Rockwool · Growing Media · Propagation Media · Base Nutrients · Dripper Systems
