Starting vegetable seeds indoors

Starting seeds indoors gives you more varieties than you'll find as plants, and a head start on long-season crops like tomatoes, peppers and eggplant. Broccoli, cabbage, kale, lettuce and onions also transplant easily. Beans, corn and carrots don't, so sow them straight into the garden.

When to sow

Count back from the date you'll plant outside. Each seed packet gives its own timing. These are typical weeks indoors before planting out:

What you need

• Cell flats or small pots with drainage holes, in a tray
• Sterile seed-starting mix
• Fluorescent or LED lights on chains, and a timer
• A spray bottle
• Plant tags and a permanent marker
• A clear plastic dome or plastic wrap
• Water-soluble fertilizer

Steps

1. 1

   Pick a spot

   Choose somewhere out of traffic and drafts, near an outlet, where the air stays above 60°F. A windowsill is a poor choice. It's cold at night, hot by day, and gives too little light, so seedlings grow tall and spindly.

   10 min

2. 2

   Fill and wet the cells

   Use a sterile seed-starting mix, not bagged topsoil, garden mix or potting mix. It's free of weed seeds and the soil fungi that cause damping off. Water it, then top it up if it settles more than half an inch below the rim. Wash reused containers and soak them in disinfectant for 30 minutes.

   10 min

3. 3

   Sow one seed per cell

   Plant each seed about twice as deep as it is wide, or as the packet says. Sow two in a cell if the seed is old, and snip the weaker seedling off at the soil line later. Tag every row.

   15 min

4. 4

   Cover and keep warm

   Put a clear dome or plastic wrap over the tray to hold moisture, and take it off when the seedlings sprout. A seed-starting heat mat under the tray speeds germination, since the mix can run 5°F cooler than the room.

   5 min

5. 5

   Hang the lights low

   Keep the lights 2 to 4 inches above the tops of the seedlings, raising them as the plants grow. Run them 12 to 16 hours a day on a timer, with a dark period each night. Too little light is the main cause of long, skinny stems.

   10 min

6. 6

   Water and feed gently

   Mist the surface or water from below by setting the tray in an inch or two of water, then pour off what's left. Once seedlings have several sets of true leaves, feed them a water-soluble fertilizer at a quarter strength once a week, with plain water between.

   5 min

7. 7

   Move up to bigger pots as needed

   Shift seedlings that outgrow their cells into pots 1 to 2 inches wider. Lift each by its root ball or a leaf, never by the stem.

   15 min

8. 8

   Harden them off

   Two weeks before planting out, set the seedlings outside for a few hours in afternoon shade, out of the wind, and bring them in before the evening cools. Leave them out longer, in more sun, each day.

   15 min

9. 9

   Check that the seedlings are stocky

   A good transplant is about as wide as it is tall, with a thick stem. Tall, floppy seedlings need the lights lower.

   2 min

Planting out

Plant hardened seedlings on a cloudy day or in the late afternoon. They may wilt in full sun at first and usually recover in a day or so. With peat or paper pots, tear the rim down to the soil line so it doesn't wick water away from the roots, and tear holes in the bottom.

Cucumbers and squash don't like their roots disturbed. Start them in pots that break down in the soil and plant pot and all.