The Q&A Archives: Green Growth On Seed Pots

Question: I have started seeds in peat pots in my basement. A green moss like film forms on surface of potting mix,plants die. The basement is cool but heated, temp around 55 degrees. Flourescent lamps 8" from pots, heat coils under trays, light about 10 hours a day.

Answer: Based on your description, it sounds like your seed starting set up needs a little adjustment. Seedlings grow best under fluorescent light set just an inch or two above the plants and left on for 14 to 16 hours a day, so it may be too dark for them. The bottom heat is usually used to germinate the seeds and then the plants are moved to an area of cool room temperature, say about 65 degrees to grow on. Your 55 degrees is a bit cool, but with ample light most plants should grow well with the possible exception of warm season vegetables such as tomatoes, peppers, and eggplants. Finally, the green mossy growth can indicate the soil is too wet. When you are trying to germinate seeds, the soil should be damp like a wrung out sponge and the containers should be covered with clear plastic to maintain that humidity level until they germinate -- you will not need to water again until they have sprouted and you have removed the cover so that they receive good air circulation. At that point, you can water gently from the top or mist the seedlings or water from the bottom. If you water by setting the peat pots in a tray of water, you will also need to allow them to drain a bit afterwards to avoid waterlogging the soil.

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