Description
The Grodan 6" Hugo rockwool block is the one most UK growers finish in. A 36mm pre-cut hole takes a standard propagation cube, so the move up is stress-free, and there is enough mass in the block to carry a plant from transplant all the way through to harvest.
Spun basalt rock, pH neutral and inert. Everything the plant gets, you put there.
Key features
- Fits standard starter cubes – the 36mm cavity takes a 36mm Grodan propagation cube cleanly, with no root disturbance.
- Takes a 6" cap – the FloraFlex 6" FLORACAP 3.0 is sized for this block.
- Moisture and air balance – holds a large reservoir while keeping oxygen at the roots.
- Flexible watering – hand water it, or run it under a dripper or a bubbler.
- Long-term use – big enough to take most crops to maturity without a slab underneath.
- pH neutral and inert – complete control over feeding and EC.
Specification
| Hole diameter | 36mm |
| Block dimensions | Approx. 150 x 150 x 140mm |
| Weight | Approx. 0.26kg dry per block, 12.59kg a box of 48 |
| Water retention ratio | Around 80% solution, 15% air, 5% fibre |
| Recommended run-off | 10 to 30% per feed |
| Pre-soak pH | 5.5 to 5.8 before transplanting |
Before you use them
Rockwool leaves the factory with a naturally high pH, so it has to be conditioned before anything goes in it. Soak for 24 hours in a weak nutrient solution under 1.0 EC, adjusted to pH 5.5. A small amount of root stimulant in the soak water lifts the EC and gets roots moving faster. Let it drain until damp rather than dripping. Skip this and you will see the first week of growth stall.
Transplant once the cutting or seedling shows at least three leaves, or roots extending about an inch below the starter cube. Feed lightly at first, then step the EC up as growth takes off.
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" | 4 x 4 x 3.1" | Veg | Pre-formed hole |
| Grodan 6" Hugo Block (this product) | 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
- FloraFlex 6" FLORACAP 3.0 – Sized for this block. Spreads the feed across the whole top surface and blocks light off the wool, which is what keeps algae down.
- Cultiwool 25cm X-Fibre Mini Slab – A 6" block sits on top of one of these for extra root mass and a bigger buffer without moving to a full slab.
- Grodan Propagation Cubes – The 36mm cube drops straight into the hole in this block.
- FloraFlex 12 Plant Bubbler System for 6" Rockwool – Purpose-built to feed twelve 6" blocks evenly in a 4 x 4ft space.
- Grodan Vital Rockwool Slab – Stand three or four of these blocks on a slab when you want one shared reservoir across the row.
Frequently asked questions
Do I have to soak them first?
Rockwool leaves the factory with a naturally high pH, so it has to be conditioned before anything goes in it. Soak for 24 hours in a weak nutrient solution under 1.0 EC, adjusted to pH 5.5. A small amount of root stimulant in the soak water lifts the EC and gets roots moving faster. Let it drain until damp rather than dripping. Skip this and you will see the first week of growth stall.
Which cap fits a 6 inch block?
The FloraFlex 6" FLORACAP 3.0. The 8" cap is for the Cultiwool Big Daddy, so do not order that one by mistake.
What is the difference between this and the version with the dripper hole?
Same block, same size. The other version has a second, larger hole intended for a dripper. If you feed from the top with a cap or a bubbler, this plain one is the one you want.
Do I need a slab underneath?
Not necessarily. A 6" block on its own will take most crops to harvest. Put it on a mini slab or a Vital slab when you want a bigger buffer between feeds, a longer cycle, or a heavier plant to stay upright.
How do I feed them?
Little and often, aiming for 10 to 30 percent run-off. Most growers run a dripper per block. See Dripper Systems, Run to Waste Systems and pH & EC Meters.
Can I move out of rockwool later?
Yes. A rooted 6" block transplants into fabric pots, into coco or into clay pebbles without checking growth, as long as the block stays moist through the move.
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Rockwool · Growing Media · Dripper Systems · Run to Waste Systems · Grow Room Irrigation
