Growing for Market in partnership with Johnny's Selected Seeds has created a library of expert information about growing and selling vegetables and flowers. Links in the article will take you to johnnyseeds.com.
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Market growers start transplants in a wide range of facilities that run the gamut from climate-controlled greenhouses to unheated hoophouses to grow lights in the basement. Although a sophisticated greenhouse may be the ideal growing environment, many growers make do with much less during their start-up phase. Luckily, seeds don’t care where they are started, as long as three conditions are provided: appropriate temperature, light or darkness, and moisture.
• Although most crops will germinate within a wide range of temperatures, germination is quickest at the optimum temperature shown in the graphs in the Johnny’s catalog. For most vegetables, the optimum temperature is quite warm, 75-90°F. This is the temperature of the growing medium, not the air temperature. Evaporation at the surface of the germinating medium can reduce the temperature 5-10 degrees below the air temperature. That’s why heating mats or cables are recommended for seed starting. With bottom heat, the growing medium can be maintained at the optimum temperature.
• Some flowers have a particular requirement for either light or darkness during germination, and some germinate more completely or quicker in the preferred situation. Vegetables, in contrast, are mostly indifferent about light during germination. The instructions on the back of Johnny’s seed packets tell you whether to cover the seed or not. If the seed packet advises leaving the seeds uncovered, a dusting of vermiculite on the seeds will help maintain moisture around them while allowing light through.
• Moisture is essential to all germination. The seed-starting medium must be thoroughly wetted before you plant, and you should cover the germinating flat with a plastic dome or piece of row cover to maintain humidity at the soil surface. However, the germinating medium needs to be well-drained, and the flats should be vented daily to prevent excessive moisture. If mold starts to develop on the soil surface, remove the cover.
As soon as the seeds germinate, they should be exposed to light and removed from the heat mat. If growing them under lights, keep the lights just an inch or two above the seedlings and raise them as the plants grow. Leave the lights turned on 16 hours a day. Grow the plants at the recommended temperature on the seed packet. Seedlings get leggy and are susceptible to damage and disease if they are grown too warm or without enough light.
The biggest threat to young seedlings is damping off, an ailment in which the stem withers right at soil level. It can be caused by several different fungi including Pythium and Rhizoctonia. Overwatering and overcrowding of seedlings are often contributing factors to the spread of the disease. It can be prevented by providing appropriate temperature, moisture, and air circulation. RootShield provides biological control and is OMRI-approved for organic production.
From JSS Advantage January 2011