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Growing to transplant size
Many growers start seeds in small containers to maximize the number of plants that can be grown on a heat mat or germination chamber. Johnny’s 20-row seed flat is well-suited for this type of system because it uses a minimal amount of germinating medium and allows seeds to be separated by variety. After the seedlings have two sets of true leaves, they can be “pricked out” and transplanted into larger cells or plugs.
Most growers keep three or four sizes of plug flats available to accommodate the needs of different crops and various field conditions. Tomatoes, melons, squash, cucumbers, and sunflowers are fast-growing plants with robust roots, so they should be grown in a larger cell, such as a 50-cell flat. Brassicas, onions, and many flowers can be grown in smaller cells, such as a 128-cell flat. Very small cells, like the 288 flat, can be used for plants that are going to be transplanted into a hoophouse, into smooth, well-prepared soil outside, or “bumped up” again into a larger container.
This strategy of germinating in a small space then transplanting to larger containers also works with Johnny’s soil block system. The Mini 20 Blocker makes 3/4” square blocks for germinating seeds. The Medium Blocker makes 2” square blocks and with the available insert, the blocks have an indentation that is just the right size for popping in a mini block.
Germination mix is a fine-textured, soilless medium with very few nutrients. It is designed primarily to be a well-drained medium for germinating seeds and keeping seedlings growing for a week or two at most. At that point, seedlings need to be transplanted into a medium with higher fertility, such as Johnny’s 512 mix. Plants that stay in the greenhouse longer than four weeks may also need additional fertility such as provided by seaweed and fish fertilizers.
From JSS Advantage January 2011