How Do I Start Seeds?

“Hi, I have the worst time starting seeds and am not sure what I’m doing wrong. Do I need to put a heating pad under the tray and a light on top? If so, can I use a regular heating pad for under them? Can I use a regular shop light above them? I cover them with plastic wrap until the seeds sprout, which hasn’t been happening, and then it gets all moldy. I just tried a tray of rock wool with 50 seeds! All I’ve got so far is mold, no sprouts. Every year I end up giving up and buying plants from the garden center. I have a lot of seeds, I collect and trade and I’d like to be able to successfully start and grow them. Thanks for your help.” Question from Lucia of Huntington Beach, California

Answer: Seed starting takes patience. The most common mistakes that gardeners make are that they plant the seeds too deeply, they overwater them, or both. Too little water is another common problem, especially when they are just beginning to sprout. A little dry soil can mean instant death to a tiny seedling. Here are my recommendations for each of your questions followed by some excellent seed-starting resources we have.

  1. Do I need to put a heating pad under the tray and a light on top? Yes, to both, though not all seedlings require bottom heat. It is best reserved for warm-season vegetables and flowers, such as tomatoes, peppers, marigolds, cleome, and salvias.
  2. Can I use a regular heating pad under them? No, regular heating pads cannot be wetted and may short out and start a fire. Seedling heat mats are not too expensive, they are safe, and just the right size for a seedling flat. (Click here to learn more.)
  3. Can I use a regular shop light above them? There are lots of lighting options, with shop-light fixtures being the most economical. Some shop-light fluorescent bulbs are specially designed for plant growth and cover more of the spectrum–up to 94%. These are the bulbs to use. In general, fluorescent bulbs are not very strong, so they must be placed just inches above seedling flats or plants for best light reception and growth.
  4. I cover them with plastic wrap until the seeds sprout, which hasn’t been happening, and then it gets all moldy. Your soil and seeds are too wet, so the whole lot is rotting before any growth can happen. Wash your pots well before you try planting again to remove any mold spores. Then fill the pots with fresh, moistened Black Gold Seedling Mix, sprinkle the seeds on top, add a light sprinkling of the mix over the seeds, and then keeping the tops lightly misted daily. (Click here to see a nice plant mister.) The soil should be kept lightly moist, never wet. For larger seeds, plant them 1 to .5 inches down, no deeper. Most seed packets recommend that you plant seeds too deeply.

From there, try reading a couple of these great articles about seed starting. We also have a video about starting tomato seeds below.

Seed Starting Article Links




Happy gardening!

Jessie Keith

Black Gold Horticulturist


Plants are the lens Jessie views the world through because they’re all-sustaining. (“They feed, clothe, house and heal us. They produce the air we breathe and even make us smell pretty.”) She’s a garden writer and photographer with degrees in both horticulture and plant biology from Purdue and Michigan State Universities. Her degrees were bolstered by internships at Longwood Gardens and the American Horticultural Society. She has since worked for many horticultural institutions and companies and now manages communications for Sun Gro Horticulture, the parent company of Black Gold. Her joy is sharing all things green and lovely with her two daughters.

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