What are Grodan Rockwool Cubes 40mm used for?
These 40mm x 40mm cubes are made for starting seeds and cuttings in a clean, space-efficient format. They're ideal for herbs, veggies, flowers, and other plants you're planning to transplant into hydroponic or soilless setups. Their consistent structure helps support even moisture, airflow, and uniform growth.
How many Grodan Rockwool Cubes 40mm can I buy?
You can buy them as singles, in bundles of 10, or in larger packs of 100—handy whether you're trialing or scaling up your propagation.
Which side of the Grodan Rockwool Cube should I use?
Use the flat side for small seeds (make a tiny divot if needed), and the indented side for larger seeds or cuttings. Some cubes come with a pre-made hole; if not, just make one gently with a clean skewer or scissors tip.
Do I need to soak Grodan Rockwool Cubes before use?
Yes—always pre-soak in pH-adjusted water (around pH 5.5–6.0) until fully saturated. Let them drain naturally; don’t squeeze, as that can collapse the air pockets roots need to thrive.
Do Grodan Rockwool Cubes contain nutrients or affect pH?
No—rockwool is inert and nutrient-free. You can use plain water to start seeds, but a mild nutrient solution is common after germination. If not pre-soaked, the cubes can cause early pH drift, so conditioning matters.
How do I water Grodan Rockwool Cubes correctly?
Keep them moist, not soaked. Avoid letting them sit in runoff. Bottom watering or light misting works well—just lift the cube to check weight. Heavy = still wet. Dry cubes are harder to rewet and can stress roots.
How deep should I plant seeds in Grodan Rockwool Cubes?
As a rule of thumb: plant seeds about 2–3 times their thickness. Most growers sow 1–2 seeds per cube. If both sprout, snip the weaker one rather than pulling it.
Why do Grodan Rockwool Cubes sometimes grow algae?
Algae shows up when the cube surface stays wet and exposed to light. It's common but manageable—keep light off the surface, allow for some drying, and improve airflow to reduce risk.
Do Grodan Rockwool Cubes need a humidity dome or heat mat?
Humidity domes help maintain moisture for germination and cloning. Bottom heat can speed root development, especially in cooler rooms or for warm-season crops.
Do Grodan Rockwool Cubes help prevent root rot?
They support healthy roots by holding moisture while allowing airflow. But overwatering and poor ventilation can still cause issues, so maintaining the right balance is key.
When should I transplant from Grodan Rockwool Cubes?
Transplant when roots start poking out and the plant looks stable—or when the cube starts drying out quickly. You can move them into soil, coco, hydro systems, or larger blocks.
Do Grodan Rockwool Cubes fit into larger cubes or blocks?
Yes—40mm is a standard starter size that often fits snugly into larger Grodan blocks designed for transplanting. Just check the hole size and format.
Can I reuse Grodan Rockwool Cubes?
You can, but most growers treat them as single-use for hygiene and consistency. If reusing, remove old roots, sanitise thoroughly, rinse, and recondition with pH-adjusted water.
Are Grodan Rockwool Cubes eco-friendly or safe to handle?
They’re not compostable, but can be reused to reduce waste. Rockwool may feel itchy—gloves are a good idea if you’re sensitive. Avoid cutting them unless necessary, as it can create dust and damage the structure.
What’s the quick-start checklist for Grodan Rockwool Cubes 40mm?
Soak in pH-adjusted water → drain (don’t squeeze) → choose the right side → sow seed or insert cutting → use a dome and warmth if needed → keep moist, not drenched → vent for airflow → transplant once roots show.
