Grodan MM 40/40 Stone Wool Mini Blocks – 40mm, Box of 2250

The 40mm block that starts a seed or a cutting and drops straight into a Delta block

Grodan MM 40/40 is a 40 x 40 x 40mm stone wool mini block with a pre-formed 6mm x 15mm planting hole, made by ROCKWOOL in the Netherlands. Each block is individually wrapped in white film, which keeps light off the roots, limits algae and steers roots downward. It is the block Grodan designed to root a seed or cutting and then block on into a 3", 4" or 6" Grodan Delta block or straight onto a slab, so the plant is never pulled out of its medium. Supplied as a full carton of 2,250: 15 blocks per strip, 45 per shrink-wrapped sleeve, 50 sleeves per box.

Key Benefits

• Inert, sterile and pH-neutral stone wool spun from basalt, with uniform density and fibre structure for even water, nutrient and pH distribution
• Pre-formed 6 x 15mm hole takes a seed or a cutting stem without tearing the fibre
• Individually wrapped - less algae, less light on the root zone, tidier handling in the propagator
• Sized for Delta blocks - the 40mm cube fits the large hole of a Grodan Delta, so transplanting is a drop-in with no root disturbance
• Suits NFT, drip, ebb-and-flood and slab culture after rooting
• Carton of 2,250 for nurseries and growers running propagation every week

Slow, uneven rooting and lime shock in fresh stone wool

Stone wool comes out of manufacture carrying residual lime, so unsoaked blocks push the root zone alkaline and stall germination and rooting. A short soak in pH 5.5-5.8 water or a weak nutrient solution neutralises it. Because the medium holds no nutrient buffer of its own, pH and EC need watching more closely than in soil or coco, and a block that is squeezed loses the air structure that makes it work.

How to Use

• Soak the blocks in water or a quarter-strength nutrient solution adjusted to pH 5.5-5.8 for 15-30 minutes, then let them drain naturally - never squeeze them.
• Sow one seed or set one cutting in the pre-formed hole and place the strip in a propagator with bottom heat and high humidity.
• Keep the blocks moist, not saturated; aim to shed about a quarter of the water before transplanting.
• Block on into a Delta 3", 4" or 6" block, a pot of coco or straight onto a slab once roots show at the base. Remove the wrap at that point.
• Feed at a low EC through rooting and step up as the plant establishes.