Successful Seed-Starting Indoors

Here at A Garden for the House, the season of indoor sowing has commenced. First up? Frost-tolerant Brassicaceae, like ‘Green Goliath’ broccoli, and also slow-to-germinate flower seeds, including Nicotiana ‘Fragrant Cloud’ and ‘Perfumed Purple,’ and Lobelia ‘Sapphire Trailing.’ These last three have been sown in the deli take-out containers pictured above. You might like to get a jump-start on some of your own annual favorites, too. The following planting-procedure has proven successful for me:

First, a seed-starting checklist…

Fluorescent Lights are essential. Use either two “cool white” tubes, as I do, or combine in your lamp one cool white with one “daylight” tube.

Seed flats can be improvised from almost anything that is deep enough to hold at least two-inches of soil. Plastic take-out containers with clear lids are ideal. I use a heated Phillips screwdriver to make drainage holes in such containers.

Cell-packs are useful for large seeds; they eliminate the need for later repotting.

Biodegradable Pots, which you can later plant directly in the garden, are useful for cucumbers, squash, zinnias and other large, quick-to-germinate seeds which otherwise do not transplant well.

A soil-less Seed-Starting Mix will reduce the chance of “damping off” (a lethal, soil-born malady).

Labels, of course, are mandatory. I use Popsycle sticks and a permanent pen to mark seed variety and date sown.

Planting, Watering, Lighting
In a flat, sow tiny, dust-like seeds (Nicotiana, or Petunia, for example), as thinly as possible in rows. Leave at least one inch between each row. Sow larger seeds in cell-packs, with up to three seeds per cell. Most seeds do not require covering with soil; I merely press them down.

Next, water the seeds from the bottom. Top watering, no matter how fine a mist you use, will invariably dislodge seeds. Therefore, set flats, cell-packs or biodegradable pots in a tray of lukewarm water until moisture is drawn up through drainage holes, and the surface soil appears damp.

Thirdly — and this is vital — cover the seed-container with a clear lid. This will not only boost humidity, but trap heat, too. If you don’t have a lid, use a sheet of plastic wrap.

Finally, set the covered flats under fluorescents, and as close to the tubes as possible. Warmth emitted from the lamps will aid in the germination process. Leave the lights on for 16 hours each day, followed by 8 hours of total darkness.

Seedling Care
When the first sprouts appear, remove the lid or plastic wrap. Then move the trays even closer to lights. One inch between sprouts and fluorescent tubes works best. Provide water as needed, but from now on with a little fertilizer mixed in. I use a quarter-teaspoon “all-purpose” food to a gallon of lukewarm water, and find this gives excellent results.

Once the second, or “true” set of leaves appears, repot seedlings sown in flats into individual cells. To do this, remove, with a spoon, a cluster of seedlings. Gently tease roots apart. Then grasp each seedling by its leaves (not its tender stem), and insert it into a cell. Add more soil around roots, if necessary, and gently firm.

For multiple seeds planted in a single cell, thin out all but the strongest-looking seedling. Do not pull unwanted stems out; simply pinch them off.

I’ll confess that starting seeds in the house is more complicated than winter-sowing them outdoors. But for those of us not in possession of a heated greenhouse, an indoor start beneath fluorescents is the cheapest means to an early harvest of vegetables, and an early crop of annual flowers. And just think of the fascinating varieties you can try!

Related Posts:
When to Start Vegetable Seeds Indoors
When to Start Annuals Indoors
Winter-Sowing 101
Gardening Under Lights – Fluorescent Setups & Culture


  1. Kevin, thanks for this timely post. I have a ton of seeds that I want to start indoors, including flat leaf parsley, which is notoriously slow.

  2. Have you ever tried one of the “self-watering” seed flats that come with styrofoam cells?

  3. Eric – the flat you are describing has received rave reviews from gardeners. I will have to try it out. Gardener's Supply (dot com) carries it.

  4. Samantha says:

    What – no heating mat?

  5. Can we REALLY start our seeds indoors now? Hallelujah!!!

  6. Samantha – if you have a heat mat, by all means use it. I have not found the device necessary here. It is at least 5 degrees warmer under the lights, and the covers over the seeds traps this heat.

    I should also add that sprouted seeds (seedlings) prefer cooler temperatures. Thus heating mats should not be used at all after germination takes place.

  7. Can you not “winter sow” these seeds? I mean, plant them outdoors, in milk jugs or other containers?

  8. Andrew – you absolutely CAN sow veggies and annual flowers outdoors in containers, ala winter-sowing. But unless your daytime temps are closer to 70 than 40, and nights are well above freezing, the seeds will sprout faster indoors, under lights.

  9. What a great use for those plastic deli containers! First you eat the food — then you grow some more! Thanks, Kevin!

Speak Your Mind