The Grodan Pro Seedling Starter Plugs are a sheet of 98 rockwool (stonewool) plugs made for starting seeds and rooting cuttings. Each 36 × 36 × 40 mm plug has a pre-formed 10 mm seed hole and holds an even balance of water and air, so young roots establish quickly and consistently across the whole sheet. When roots show through the plug, move it straight into coco, rockwool blocks or a hydroponic system with no transplant shock from disturbed roots.
A consistent start for every seedling
Stonewool is spun from natural basalt rock into a fine fibre that holds water while keeping plenty of air space around the roots. Every plug in the sheet is the same density, so every seed or cutting starts in identical conditions and the batch comes up evenly. The medium is sterile and inert, which means no soil-borne pests and full control over what the young plant is fed.
Easy to handle, easy to move on
The plugs sit together as one sheet that fits a standard 10 × 20 propagation tray, so the whole batch moves in and out of a dome in one piece. Tear off single plugs as each one is ready. Because the roots stay inside the plug, you transplant the plug and all, straight into coco coir, a larger rockwool block or a net cup in a hydroponic system.
Full specifications
| Manufacturer | Grodan |
| Product | Grodan Pro A-OK starter plugs, AO 36/40 |
| Material | Stonewool (rockwool) |
| Plugs per sheet | 98 |
| Plug size | 36 × 36 × 40 mm (1.5 × 1.5 × 1.6″) |
| Seed hole | 10/10: 10 mm diameter, 10 mm deep |
| Tray fit | Standard 10 × 20 propagation tray |
| Sold as | 1 sheet of 98 plugs per unit |
| Suits | Seeds and cuttings, before moving into coco, rockwool blocks or hydroponics |
FAQ
Do I need to soak the plugs first?
Yes. Soak them in pH-adjusted water, around pH 5.5, then let them drain before sowing. A moist plug rather than a waterlogged one gives the best germination.
Can I plant the plug into coco?
Yes. It's one of the most common ways to grow. Once roots show through the plug, set the whole plug into coco coir. There's no need to remove the rockwool.
Can I use them for cuttings as well as seeds?
Yes. The plugs suit rooted cuttings as well as seeds. Push the cutting stem into the hole and keep humidity high until roots form.
Do the plugs contain nutrients?
No. Stonewool is inert, so seedlings rely on what you feed them once their first true leaves appear. Start with a light, diluted feed.
Will the sheet fit my tray?
The sheet is sized for a standard 10 × 20 propagation tray. Single plugs tear off cleanly if you want to use part of a sheet in a smaller tray.