Grodan MM50/40 6/15 Block
Best starter cubes for hydroponic seed propagation and seamless transplanting.
The Grodan Rockwool Grow Cubes (MM 50/40) are expertly designed for seed starting and propagation. These small, 2" x 2" x 1.5" cubes come conveniently wrapped and sold in sheets of 24, guiding roots downward for easy integration into larger systems. Made from molten rock spun into unique fibers, Grodan cubes offer superior nutrient and oxygen retention, promoting accelerated plant growth. Their uniform design and improved drainage grooves make them ideal for hydroponic setups and seamless transplanting into various growing media, supporting plants through every stage.
$18.08
Owner Satisfaction
4.7
/ 5
Category Rank
11
/ 1247
#11 in Soil
Price vs Category Average
-64%
Below average
Cube Dimensions
221.5
/ in X in X in
Who it's for
- Hydroponic enthusiasts requiring precise moisture and aeration control
- Commercial growers seeking consistent, pathogen-free root development
- Indoor gardeners aiming to reduce plant transplant shock
Who should skip it
- Gardeners preferring a simple, ready-to-use planting medium
- Users sensitive to skin or respiratory irritants
- Eco-conscious growers prioritizing biodegradable or sustainable materials
Performance breakdown
Root development
Engineered fibers actively encourage downward root growth for healthier starts.
Oxygen retention
High-porosity structure ensures roots receive consistent oxygen for rapid development.
Transplant efficiency
Uniform block design makes moving seedlings into larger systems seamless.
Moisture management
Superior absorption capacity keeps hydration levels stable during critical growth stages.
Drainage performance
Integrated grooves effectively prevent waterlogging in hydroponic setups.
System compatibility
Standardized sizing integrates perfectly with common propagation and hydroponic trays.
Key Specs
Cube Dimensions
2 in X 2 in X 1.5 in
Quantity per Sheet
24 cubes
Material
Rockwool (Stonewool) made from molten rock fibers
Packaging
Plastic wrapped cubes
Full Case Quantity
60 sheets
Part Number
RWMM5040
Design
Delta blocks with improved drainage grooves
Intended Use
Seed Starting
Features
- Engineered fibers for specific plant stages
- High nutrient solution absorption
- Retains significant oxygen for growth
- Graduated sizing for easy transplanting
- Compatible with AO 36/40 plugs
- Guides roots downward effectively
- Uniform blocks for hydroponic integration
- Supports rapid plant development
What customers say
Customers highly value the Grodan MM50/40 blocks for their exceptional quality and dependable performance in hydroponics. A key highlight is the superior structural integrity, which maintains aeration crucial for healthy root growth and avoids media breakdown. Furthermore, the predrilled holes significantly simplify the seeding and transplanting process, offering users considerable time savings. This reliability and consistent success rate confirm the product's foundational role in effective growing, making it a worthwhile investment.
Know before you buy
These blocks are specifically engineered for seed starting and early-stage propagation. Their design encourages roots to grow downward, making them an ideal foundation before transplanting into larger hydroponic or soil-based systems.
Yes, the MM50/40 blocks are designed to be compatible with Grodan AO 36/40 plugs. This allows for a seamless transition as your seedlings develop and require more space.
The improved drainage grooves prevent water from pooling at the base of the cube. This ensures the root zone maintains an ideal balance of moisture and oxygen, which is critical for preventing root rot and promoting rapid development.
While these cubes are ready to use, it is standard practice to soak them in a pH-adjusted nutrient solution before inserting your seeds or plugs. This ensures the rockwool is properly buffered and ready to support immediate growth.
While they are optimized for hydroponic setups, they can be used for soil-based gardening as a starter medium. Once the roots have established and grown through the bottom of the cube, you can transplant the entire block directly into your potting mix or garden bed.
The cubes are sold in sheets of 24. If you are purchasing a full case, it will contain 60 of these sheets, totaling 1,440 individual cubes.
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