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Greenhouse Updates: Mar 8, 2017

Tips for Producing Transplants from Seeds
Mar 8, 2017

Begin by using fresh seeds. 

If using leftover seeds from the previous year, test for germination first.  Place a specific number of seeds, such as 10, 50 or 100 on a moistened paper towel. Fold the moistened paper over the seeds and put it in a plastic bag in a warm place. Take the paper towel out and inspect the seeds twice a day, spraying with water as needed to maintain moisture around the seeds. After the usual number of days required to germinate that variety, count to see how many have germinated and calculate the percentage of germination.

Note: If growing basil transplants use steam treated seeds to help avoid introducing Basil downy mildew caused by Peronospora belbaharii which can be seed-borne.

Test the growing medium for pH and soluble salts. For optimum seed germination for most crops use a growing media with a pH of 5.7 to 6.2 and low soluble salts.  Many seedling problems often relate to improper pH and high soluble salts. 

Also test irrigation water by submitting samples to a commercial laboratory. How to Take a Water Sample:

To prevent damping-off, use a preventative biofungicide (protectant), either a commercial growing medium where it is already incorporated into the media, or as a spray or drench. Damping-off is a disease of germinating seeds and young seedlings. Several fungi cause damping off including Rhizoctonia and Alternaria and the water molds Pythium and Phytophthora Streptomycin lydicus (Actinovate SP), Bacillus amyloliquefaciens D 747 (Double Nickel, Triathlon BA) and Trichoderma harzianum, strain T-22 (Rootshield), and Trichoderma virens strain G-41 (RootShield Plus+) can all be used for seedlings (including vegetable seedlings). Note: Actinovate SP, RootShield Double Nickel, Triathlon BA are OMRI listed (organic).

Properly handle the growing medium to minimize compaction and provide adequate air space for healthy rooting.  To minimize compaction, lightly fill containers, cell packs and plug trays with growing medium and brush away the excess. Do not pack down, tamp down, or tap down filled pots on the bench.  Never stack (nest) pots and trays directly over one another.  Compaction impairs root growth and leads to root rot diseases.

Add water to the growing medium before it is placed into the container. It is best to moisten, then mix and allow to sit overnight prior to use. If that is not possible, wait at least a couple of hours after adding the water to help the hydration process. When water is added to dry components such as peat, they hydrate and swell. This swelling helps to create more aeration by preventing the particles from nesting within one another. This is especially important in plug production.

How much water to add to the mix? Plug mixes should have a 2:1 water: dry substrate ratio (67% moisture content). The rule of thumb is, the smaller the cell, the more water to add prior to planting.

Test for moisture content. The medium should be damp to the touch but not wet. Take a handful of medium after adding moisture and squeeze it. No drops of moisture should come out. When your hand is opened, the medium should still retain its shape. If it falls apart right away, it is too dry. When pressed lightly, it should fall apart. The correct amount of moisture will result in less shrink or settling of the medium.

For more information see: "Greenhouse Substrates and Fertilization" , by Douglas A. Bailey, William C. Fonteno, and Paul V. Nelson Dept. of Horticultural Science, NCSU

When sowing in open seed flats, sow in rows. Seedlings are easier to handle and damping- off disease is easier to manage. However, if seeds are sown too thick, crowded seedlings will result in stretched plants and create high humidity around seedlings that favor damping-off diseases, not to mention the difficulty to transplant.

If using plug trays, place seed in the middle of the cell. Seed placed near the edge of the cell are likely to desiccate.

If covering seeds, use medium or coarse vermiculite to create a micro-environment of high humidity. Fine vermiculite can result in buried seeds. Some seeds need light to germinate; these are covered lightly or left uncovered. A mist system will help to keep these moist.

Move seed trays into a germination chamber or propagation area as soon as possible after sowing to receive necessary humidity and water. It helps to group crops by temperature needs. Do not allow germinating seeds to be interrupted by dryness by remaining in the seeding area too long.

Warm temperatures and uniform moisture are needed to ensure successful germination and get the plants off to an even start, whether seeds are germinated on the bench or in germination chambers. When germinating on open benches, most growers cover seedling/plug trays with a porous fabric (permits water to pass through at a slow rate) to maintain uniform moisture. Care must be taken to remove covering just after germination.

Remove flats from the germination chamber as soon as radicles break through the seed coat to avoid seedling stretching. Experience and experimentation with your total seeding system is the key to uniformity and success.

Tina Smith, Douglas Cox, UMass Extension and Leanne Pundt, UConn Extension


McGrath M.T. Expect and Prepare for Basil Downy Mildew, Cornell University

Bartok J. Plug Extractors, Watering Stations and Tagging Machines, University of Connecticut Extension

Bartok J. Seeders, University of Connecticut Extension

Sawanya M. 2010. Growing in the Green: It's time for a tune-up. Greenhouse Canada

Propagation Resources, University of Massachusetts Extension

Vegetable Transplant Production, New England Vegetable Management Guide