Description
The Cultiwool 8" Big Daddy Block is the biggest rockwool block you can buy in the UK. 20 x 20 x 19.5cm of stone wool, enough root room to take a large plant through its whole lifecycle without a slab underneath it.
Grodan do not sell an 8 inch block into the UK. Cultiwool do, and it costs less than the Grodan equivalent does elsewhere.
Why growers step up to an 8 inch
- Root room – the whole point. More substrate means a bigger plant without the root zone becoming the limit.
- Physical stability – the extra mass holds a top-heavy plant upright when it is carrying weight late in flower.
- A bigger buffer – more volume means slower swings in water content and EC, so a missed feed is not a crisis.
- Algae and pest resistance – the block ships with a resistant cover that keeps light off the wool.
- Crop steering – it re-saturates quickly and evenly, and water content and EC distribute uniformly, which is what makes a steering strategy repeatable.
Specification
| Block dimensions | 20 x 20 x 19.5cm (8") |
| Material | Cultiwool stone wool, inert and pH neutral |
| Cover | Light-blocking resistant wrap |
| Takes | An 8" Flora Cap |
| 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. On a block this size, give it the full 24 hours, and let it drain properly before you put a plant in it.
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 | 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 (this product) | 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 8" Flora Cap v2.0 – Fits this block exactly. Spreads the feed across the whole surface and blocks light off the wool.
- Cultiwool 25cm X-Fibre Mini Slab – Stand the Big Daddy on one of these when you want an even bigger reservoir under a very large plant.
- Grodan 6" Hugo Block – The rung below. A rooted 6" block transplants straight into an 8" if you run a two-stage move.
- Octa-Mitter 360 Dripper on Stake – Adjustable 0 to 60 L/h, enough flow to wet a block this size properly.
Frequently asked questions
Why can't I buy a Grodan 8 inch in the UK?
Grodan do not distribute that size here. Cultiwool make the same thing to the same job spec and it is available to UK growers now, which is why we stock it.
Do I still need a slab under it?
Usually not. 20 x 20 x 19.5cm is enough substrate to finish a large plant on its own. Add a 25cm mini slab underneath only if you want a longer interval between feeds.
Do I have to soak it first?
Yes, and on a block this size do not rush it. 24 hours in solution under 1.0 EC at pH 5.5, then drain until damp rather than dripping. A partially wetted block gives you dry pockets that never come back.
How do I feed a block this big?
More volume per feed than a 6 inch, but the same 10 to 30 percent run-off target. A cap or a multi-outlet dripper spreads it better than a single point. See Dripper Systems and Run to Waste Systems.
Browse more
Rockwool · Growing Media · Dripper Systems · Run to Waste Systems · Grow Room Irrigation
