How to Gain Even Seed Germination in Plug Trays

How to Gain Even Seed Germination in Plug Trays

Seed Germination

With the right preparation before sowing seed and a diligent approach to managing your environment and culture, you can make sure that you maximize germination to give your plugs the best start possible.

With spring production starting soon, seedling plug production is in full swing at many greenhouses. As with any crop, uniformity is key to produce high-quality plants efficiently and economically. For seed-propagated crops, this starts in the plug tray.


According to an e-Gro Alert report from Iowa State University’s Chris Currey, the first step in producing seed-propagated annuals and perennials is growing seedling plugs for transplanting into containers for finishing. Seed germination is the first step in seedling development, and it consists of two stages. In Stage 1, the seedling root or radicle emerges from the seed. In Stage 2, cotyledons emerge and develop while the radicle penetrated the growing substrate. Once these two stages are over, germination is complete and the seedling moves into the growth stages (Stages 3 and 4, true leaf development and toning, respectively).

While each stage of plant growth is important, germination (and the stages that comprise it) is the most crucial for growing seedling plugs. There are several factors that growers should keep in mind as they prepare to and proceed with growing plugs.
• Uniform flat filling. Filling flats uniformly before seeding will help improve uniformity in germination of plugs. Cells with less substrate will dry out quicker than those with more substrate, and will generally take longer to germinate due to the lower moisture around the seed.
• Moisture management. Availability of substrate moisture is critical to uniform seed germination. Access to water is critical for the chemical and physiological processes of seed germination to occur. The moisture during germination can be maintained in a variety of ways, including careful irrigation, humidity management, and using a covering.
• Light. While a covering can be used as a tool for managing moisture, some seeds need to be covered to promote germination while others cannot be and require light. Crops like begonia, impatiens, and petunia should not be covered so they are exposed to light during germination, while crops including phlox and vinca should be covered to exclude light for better germination.
• Temperature. During germination, the temperature should be warmer than it would be as seedling development progresses into true leaf development and toning. If temperatures are too warm or too cool, germination can be delayed and uniformity can diminish, contributing to less-than-uniform results.

Read the complete e-Gro alert here.