Most vegetable seedlings are sown in commercial seedlings trays. These trays are made of either polystyrene or hard plastic. The numbers of plugs per tray vary from 50 to 300 depending on plant characteristic. The most common tray used is the 200 plug tray made from polystyrene.
The trays are 30 cm wide, 70 cm long and 5 cm high. Each plug is 2 cm x 2 cm and the opening is tapered towards the bottom of the tray. The reason that the seedlings can easily be removed once they are ready for transplanting. It is important that seedling trays should never touch the soil and that there should be at least 10cm of space between the tray and the ground.
It is important to follow the basic steps in preparing and sowing the seed in seedling trays to ensure healthy seedlings and a high germination percentage. The following steps should be followed:
- Place a seedling tray on a clean flat surface such as on a veranda, the back of a truck, on a trailer or on a piece of plastic that has been properly cleaned. Never place the trays on an area where livestock have walked.
- Fill the seedling tray with the chosen seedling mixture (A, B, C or D: see our post on seedling mixtures).
- Drench the seedling tray(s) with a watering can or hose pipe with a nozzle that spreads the water evenly in a wide area. Do not use a bucket or hose without a spray nozzle. The water falling on the seedling mixture will fall so hard that the seedling media will splash out of the plugs. The purpose is to drench lightly so that the seedling mix will settle into the plugs.
- The next step is extremely important. Press lightly with your thumb in each plug so that the media is depressed not more than 1 cm. This will allow a small indent for the seed to rest in.
- Sow one seed in each hole.
- Once all the seeds have been sown, lightly sprinkle dry seedling mix on top of the seeds so that they are just covered. The seed should not have more than 0.5 cm of seedling mixture covering them.
- Lightly press with your thumb in each plug so that the seed is compressed and in contact with growth medium.
- Irrigate lightly a second time over the tray(s).
- Place the tray on top of bricks or a specially designed structure in the nursery.
There is usually no need to thin seedlings out, however, it does happen that two seeds are placed into one plug. The weakest plant should be removed one week after emergence. Doing it later will damage the root system of the adjacent seedling since their root system start to entangle after one week.