Starter Plug
Definition: A starter plug is a small, pre-formed cube or cylinder of growing medium, usually rockwool, compressed peat or coco, or a bonded organic blend, used to germinate seeds or root cuttings. Plugs hold moisture and air evenly around young roots and transplant easily into soil, coco or hydroponic systems without disturbing the seedling.
How Starter Plug works
Planting straight into a big pot works, but tiny seedlings in a large volume of wet soil are easy to overwater. A plug gives the young root a small, controlled zone where moisture and oxygen stay balanced. When roots poke through the sides or bottom, you move the whole plug into its next container.
Common plug types
- Rockwool: spun mineral fiber, sterile and uniform. It starts with a high pH, so soak cubes for an hour in water adjusted to about 5.5 before use. A favorite for hydroponics.
- Peat or coco pellets: flat discs that swell when soaked. Cheap and easy, and roots grow right through the mesh.
- Bonded organic plugs: composted bark or peat held together with a plant-based binder. Very forgiving for seeds and clones.
Using a plug
Squeeze out excess water so the plug feels like a wrung sponge. Drop the seed into the hole about 0.25 inch (6 mm) deep, root down if already sprouted, and pinch the top closed. Keep plugs in a tray under a humidity dome at 72 to 80°F (22 to 27°C). Transplant once 2 or 3 white roots show outside, usually 7 to 10 days after sprouting. Never let a plug dry out completely, because dry rockwool is hard to rewet evenly.