What are Grodan Rockwool SBS Cubes made of and how many come in a tray?
Grodan SBS Cubes are small 36mm rockwool blocks designed for seed starting and cloning. Each tray includes 77 cubes. Rockwool is a clean, inert mineral fibre medium—not soil or coco—and provides excellent water and air balance for propagation.
What are Grodan SBS Cubes used for?
They’re ideal for germinating seeds, rooting cuttings, and starting vegetable or herb seedlings like tomatoes, chillies, and basil. Widely used in hydroponic and soil-based gardens, they support fast, uniform root development in early plant stages.
How do I prepare Grodan SBS Cubes before planting?
Pre-soak the cubes in pH-adjusted water (around 5.5–5.8) until fully saturated. You can use plain water or a mild nutrient solution. Let them drain naturally—never squeeze, as it reduces the vital air space in the fibres.
How do I plant seeds or insert cuttings into Grodan SBS Cubes?
Drop seeds about 2–3x their thickness into the pre-made hole (or make one if needed). For cuttings, use a clean tool to make a snug pilot hole. Cloning gel is optional but can speed up rooting for fussier plants.
Should I use a humidity dome or bottom heat with Grodan SBS Cubes?
Yes—humidity domes help early moisture retention for seeds and cuttings. Bottom heat is beneficial for warm-season crops and clones, especially in cool environments. Just avoid overheating or trapping too much moisture without airflow.
What’s the best way to water Grodan SBS Cubes?
Water gently from the top or briefly bottom-water, then let them drain fully. The cubes should feel moist, not soaked. Use lift weight to judge moisture—don’t water based only on surface dryness. Avoid leaving cubes sitting in runoff.
Can Grodan SBS Cubes grow algae or mold?
They can if cube tops stay too wet and exposed to light. Use propagation covers or collars, improve airflow, and avoid overwatering to reduce algae, mold, and fungus gnat risks.
When and how do I transplant from Grodan SBS Cubes?
Transplant once roots poke from the sides or bottom. You can move cubes into soil, coco, hydro systems, or larger rockwool blocks. Just adjust watering based on the surrounding medium and plant size.
Are Grodan SBS Cubes safe and easy to handle?
Yes—they’re safe for edible crops and widely used in commercial horticulture. Rockwool can be a bit itchy, so wear gloves if sensitive. Cutting cubes isn’t recommended, as it can create dust and damage their structure.
Can I reuse Grodan SBS Cubes?
They're best treated as single-use to avoid disease and salt buildup. If reusing, thoroughly remove roots, sterilise with diluted peroxide or bleach, rinse well, and recondition. Even then, results may vary compared to fresh cubes.
Do Grodan SBS Cubes hold nutrients or need specific feeding?
They don’t buffer nutrients like soil. Use a mild nutrient solution once seedlings show true leaves. Occasional runoff helps prevent salt buildup. Avoid feeding at full strength in early stages, and monitor EC for healthy growth.
Why are my seedlings yellowing or cuttings wilting in Grodan SBS Cubes?
Common issues include lack of nutrients after germination, overwatering, incorrect pH, cold temps, or low humidity. For cuttings, wilting may also indicate poor contact, dryness, or too much light too early.
Can I use Grodan SBS Cubes outdoors?
You can, but they dry out faster in direct sun and wind. Algae can form on exposed surfaces. Outdoor use works best in a shaded, protected propagation setup like a mini greenhouse or under shade cloth.
What’s the benefit of using the Grodan SBS Cube tray?
The tray keeps cubes stable, organized, and easy to handle during watering or transplanting. You can remove cubes individually as needed. Cutting the tray is possible but may reduce handling convenience.
How should I store unused Grodan SBS Cubes, and do they expire?
Store dry cubes in a sealed, dust-free area. They don’t expire if kept dry and clean. Once moistened, treat them as “in use” and avoid long-term storage without proper sanitation.
