What Is a Plug Plant? Tiny Seedlings Explained
A plug plant is a seedling grown in a small cell of growing medium. University of Florida IFAS Extension notes a single tray can hold from 220 up to 800 plants. Growers buy plugs to pot on into larger containers. UMass Amherst Extension notes plugs dry out quickly because of their small volume of medium.
The short answer
A plug is a young seedling grown in a small cell of a multi cell tray. University of Florida IFAS Extension notes a finished plug has more than four expanded leaves plus is ready for transplanting. Water plugs as soon as they arrive, check them often plus pot them on at the same depth.
How are plug plants grown?
University of Florida IFAS Extension notes plug flats are filled with growing medium plus seeds are sown into each cell by machine. It describes four stages of plug growth.
| Stage | What happens | Ready to pot on |
|---|---|---|
| 1 | Root emerges from the seed | No |
| 2 | Seed leaves spread | No |
| 3 | Three or four true leaves unfold | Not yet |
| 4 | More than four expanded leaves | Yes |
Source: University of Florida IFAS Extension.
When should plugs be potted on?
UF/IFAS calls a plug finished once it has more than four expanded leaves. UMass Amherst Extension advises letting new plugs settle for 24 to 48 hours before transplanting. It advises planting plugs at the same depth as the original plug.
Can plugs go straight into the garden?
Penn State Extension advises hardening off bedding plants before they go from gentle indoor to harsh outdoor conditions. Most gardeners pot plugs on first so the roots grow bigger. University of Illinois Extension notes direct sowing suits crops that do not transplant well instead.
How to: step by step
- Unbox plugs as soon as they arrive.
- Water them well with clean water.
- Check the trays two or three times a day.
- Water the trays 2 to 3 hours before transplanting.
- Plant each plug at its original depth.
- Harden off before moving outdoors.
Troubleshooting
Plugs drying out fast: the small cells hold little water. Look at them more often.
Dry plugs at the tray edges: watering missed the edges. Water the outer cells fully.
Wilting after planting out: the plants were not hardened off. Shift them outdoors in steps.
For related reading see potting up cannabis seedlings, life cycle of a marijuana plant plus make cannabis clones. Kind Seed Co also stocks cannabis seeds.
Sources
- Seed germination: plug production, UF/IFAS Plant Propagation
- Transplanting plugs and grouping plants, UMass Amherst Extension Greenhouse and Floriculture
- Gardening terms defined, University of Illinois Extension
- How hardy are your annuals?, Penn State Extension
FAQ
How many plugs fit in one tray?
University of Florida IFAS Extension notes a single sheet holds from 220 up to 800 plants depending on cell size. Small home packs hold far fewer. The smaller the cell, the faster the plug dries out plus the sooner it needs moving into a larger pot.
Should plugs be watered before transplanting?
Yes. UMass Amherst Extension advises watering the plug trays thoroughly 2 to 3 hours before transplanting. This helps the plugs slide out of the cells. It advises never planting plugs that are dry. Fill the new pots with moist growing medium plus make a hole for each plug first.
What is potting on?
Potting on means moving a plug into a larger container so its roots have more room. UMass Amherst Extension advises filling the new pots with moist medium plus making holes ready for the plugs. It advises handling plants gently plus planting at the same depth as the original plug.
Do plug plants need feeding?
UMass Amherst Extension advises a general purpose fertilizer after the first watering. It advises about 50 to 60 ppm of nitrogen at every other watering for greenhouse plugs. Home gardeners can use a diluted liquid feed at a similar rate while the plugs wait to be potted on.
What stages does a plug go through?
University of Florida IFAS Extension lists four stages. First the root emerges, then the seed leaves spread, then three or four leaves unfold. A finished plug has more than four expanded leaves. Done well, a plug tray produces very even seedlings ready for transplanting.
