Plugs are small plants grown in special plant propagation trays that hold from 70 to 800 plants, each in a small compartment, or cell. The resulting root ball looks like a small plug when you pop it out of the tray. Plug trays let you grow a large number of seedlings for annual bedding plants, including petunias (Petunia X hybrida), for transplant in a compact space. Because petunia seeds are so tiny, they are usually germinated in an open tray and the clusters of sprouted seeds separated and transplanted into plug trays so they can develop with just one plant per cell.
Things You'll Need
- Plug tray
- Potting soil
- Pencil or chopstick
- Paper towel
- Table fork
Watch your sprouted petunia seeds for their first true set of leaves. True leaves are the second set of leaves any seedling produces. The small oval leaves that emerge first are called seed or cotyledon leaves. Petunia leaves are elongated ovals that are slightly fuzzy.
Fill a plug flat with moist potting mix. Poke a small hole in the center of each cell with a pencil or chopstick.
Lift out a section of petunia seedlings with a fork. Work the utensil under the seedlings, scraping the bottom of the tray to avoid hitting the young roots.
Set the clump of seed-starting mix and seedlings on a piece of moist paper towel. Break up the clump gently with the point of the pencil or the tines of the fork. Discard the weakest seedlings and avoid handling the stems or roots of the petunias you are keeping.
Pick up one petunia by its leaves to avoid damaging it stem. It will not recover from stem damage at this stage. You can also catch the plant under its pair of leaves with the tines of the fork instead picking it up with your fingers.
Fold one end of the damp paper towel over the remaining seedling to keep them moist while you work.
Lower the petunia seedling straight into a hole in one of the cells. Set the plant so its leaves are just above the soil level. Ensure the hole is deep enough so the root doesn't double over in the bottom of the hole.
Firm the soil gently around the stem with your finger.
Repeat until you fill each plug cell with a petunia seedling.
Tips & Warnings
- Petunias need 10 to 12 weeks from seed to garden transplant. Germinate petunia seed on top of moist seed-starting mix 10 to 12 weeks before you plan to transplant them into the garden -- when soil is at least 60 degrees Fahrenheit and there is no danger of frost.
- Keep trays moist in an environment that is 60 to 65 F. They should receive 16 to 18 hours of light -- commonly under fluorescent lights -- per day so they will be ready to bloom at planting time.
- Petunias can be directly seeded into plug cells to avoid transplanting if you use pelleted seed -- seed with a small amount of clay around it to give it a uniform and practical size for easy planting. Pelleted seed can be more expensive and difficult to find in a wide variety of petunia colors and cultivars.
- North Carolina State University Extension: Plant Propagation - Basic Principles and Methodology
- North Carolina State University Extension: Petunia X Hybrida
- Discovering Annuals: Petunia - Raising Petunias From Seed
- University of Minnesota Extension: Growing Petunias
- Thompson and Morgan: Handling Small Seeds
- The Washington Post: Why You Should Try Pelleted Seeds
- Photo Credit Medioimages/Photodisc/Photodisc/Getty Images