Grodan Improved Mini Block MM 40/40 6/15 Plugs, 1.5Inches x 1.5Inches x 1.5Inches, 2250 per box (unwrapped)

The Grodan Improved Mini Block MM 40/40 is a 1.5-inch stone wool propagation plug designed for high-volume cloning and seedling programs. Each box contains 2,250 unwrapped blocks — the cellophane sleeve around individual strips has been removed, but the cube wrapping on each block remains intact. This format is the standard commercial choice when growers pre-soak and stage large quantities of plugs at once without the handling overhead of individually wrapped strips.

Grodan Improved Mini Block MM 40/40 Specifications

The MM 40/40 designation refers to the block’s nominal 40 mm × 40 mm footprint (approximately 1.5 inches square). The Improved series uses Grodan’s refined stone wool fiber structure for more consistent water distribution and air-to-water ratio compared to earlier Mini Block generations.

Why Choose the Grodan Improved Mini Block MM 40/40

Stone wool remains the substrate of choice for many commercial propagation operations because it provides a stable, inert matrix that holds moisture while retaining significant air porosity. The Grodan Improved Mini Block builds on this with the following practical advantages:

• Consistent fiber structure: The Improved series uses a refined manufacturing process that results in more uniform water retention across the block. This reduces dry spots and wet pockets that can cause uneven rooting in large trays.
• Intact cube wrapping on each block: Even in the unwrapped (no-cellophane) format, each individual block retains its cube wrapping. This keeps the block geometry stable during handling and pre-soaking, so blocks do not compress or deform before transplant.
• High-volume commercial format: 2,250 blocks per box means fewer reorders and lower per-unit handling cost for operations running continuous propagation cycles. The unwrapped format also reduces packaging waste compared to individually cellophane-sleeved strips.
• Compatible with standard propagation trays: The 1.5-inch block dimension fits standard 50-cell and similar propagation inserts commonly used in commercial clone rooms and seedling stations.
• Inert and pH-stable: Stone wool does not contribute organic matter or alter nutrient solution chemistry, giving growers direct control over EC and pH from day one of propagation.

Best Uses for the Grodan Improved Mini Block MM 40/40

The MM 40/40 6/15 is sized and formatted for propagation — specifically the early rooting stage before transplanting into a larger grow block, pot, or slab. Growers who work through a large volume of cuts or seeds per week will get the most value from the 2,250-count case.

• Cutting propagation (cloning): The 1.5-inch block is a standard size for inserting stem cuttings. The block holds enough moisture to support early callus formation and initial root development without waterlogging.
• Seed germination: Blocks can be used for germinating seeds that will later be transplanted onto a larger Grodan block or into another substrate. The inert matrix does not interfere with germination chemistry.
• Commercial scale operations: At 2,250 units per box, this format is intended for facilities running dozens to hundreds of cuts per propagation cycle — commercial cannabis production, herb and leafy green starts, and professional propagation services.
• NFT and drip-feed hydroponic systems: Mini blocks transplant cleanly into many hydroponic setups, including nutrient film technique channels and top-drip rockwool slab systems, because stone wool does not break apart or contaminate the system as the roots grow through.
• Bridging to larger substrates: The MM 40/40 is commonly used as the first propagation stage before moving rooted cuttings onto a larger growing media for the vegetative phase. The block can be set directly on top of a slab or into a container without disturbing the root zone.

Compatibility

The Grodan Improved Mini Block MM 40/40 is designed to work within Grodan’s wider stone wool product line, but it is also compatible with most standard hydroponic and propagation equipment.

Propagation trays: The 1.5-inch block fits 50-cell flat inserts and similar propagation tray formats. Growers should confirm the inner cell dimension of their specific insert before placing a large order, as cell geometry varies by manufacturer.

Irrigation: Compatible with hand-watering, ebb-and-flow flood tables, and low-volume drip emitters. The block should be pre-soaked at pH 5.5–6.0 before use. Avoid over-saturating — Grodan’s Improved fiber structure is intended to self-regulate moisture retention, but excess standing water will still reduce oxygen availability at the root zone.

Transplanting: After roots are visible at the bottom and sides of the block, the rooted plug can be transplanted directly onto a Grodan grow slab, into a stonewool block of the next size up, or into a container filled with another media. If moving to a soil or coco-based media, place the block so roots can grow out without the stone wool being buried deeply, as stone wool does not decompose. If you are also running containerized plants, fabric pots work well for receiving transplants from these blocks, since the air-pruning design encourages outward root development consistent with how rockwool propagation is structured.

Nutrient solutions: Compatible with all standard hydroponic nutrient lines. Stone wool is inert and will not react with or buffer nutrient solutions, so EC and pH readings from the block’s runoff will closely track the input solution.

Sources & Further Reading