Sowing seeds indoors

Sowing seeds indoors is a March-April-May ritual for me. After perusing seed catalogs during cold January/February days, and ordering what I need/want to add to my collection of seeds saved from previous years, it’s really nice to finally start sowing seeds into soil.

Gardeners develop their own routines for starting seeds. Here’s mine, slightly updated from a January 2013 post explaining the same.

  • The container: black plastic flats saved from prior nursery purchases. Paper cups, rectangular plastic vegetable containers, small pots, or just about any food-safe container that holds a couple of inches of soil and has drainage.


  • The prep: fill containers with light weight potting mix, gently packed down so the soil  gives a little … like a sponge. Cut-to-size newsprint will keep soil from escaping through holes.


  • The planting: I plant seeds into dry potting mix. Scatter small seeds, such as lettuce and radish, in rows or over the entire flat, then sprinkle with a light coating of soil. Larger seeds are inserted a bit deeper into the soil. Use a blunt pencil to create rows and push larger seeds to the correct depth. The general rule: plant as deeply a seed’s diameter.

OLYMPUS DIGITAL CAMERA              Label Thumb

  • The watering: place flats into a larger, leak-proof tray containing about an inch of water. The soil absorbs water through the drainage holes in the bottom of each flat. After sowing, moisten the top of the soil with a gentle spray from a sink sprayer or a clean spray bottle. Thoroughly moisten the soil initially, then keep the soil moist – not soggy. Cover the flats with clear plastic to maintain moisture until seeds sprout, then remove the plastic to allow air circulation.
  • The lighting: Most seeds don’t need light until after they sprout – there are some exceptions but the seed packets should explain this. Indoor-started seedlings usually become leggy; very few homes receive enough light to prevent this. Grow lights, kept as close to the plants as possible, without actually touching the top leaves, will insure plants do not grow tall and spindly before it is time to harden them off outside.
keep indoor grow lights close to seedlings to prevent seedlings from growing tall and spindly.

Keep indoor grow lights this close to seedlings to prevent  tall and spindly growth.

I use a home-made light rack (thanks to dear Hubby) that allows me to adjust florescent lights to the height needed. As seedlings grow, I raise the lights.

Home-made grow light rack for indoor seed starting.

Home-made grow light rack for indoor seed starting.

  • Continued care: Even under grow lights, rotate seed flats to encourage even growth. Water when the top half of the soil is dry, preferably a little at a time into the bottom of the tray. Add only enough water for the flats to soak up through their holes. If you come back an hour or two later to find flats in standing water, drain the tray. Plants, especially seeds and seedlings, will rot in constantly over-soaked soil.

Some additional tips:

  • Label all flats/pots. Repurpose saved plant tags from previous purchases, create labels attached to toothpicks for each flat, or attach sticky labels to the outside of each flat.
  • Keep a calendar, journal or some sort of plant diary to track your methods, planting dates, successes, and failures. I find it useful to note, in the upper right corner of each seed packet, the year they were packed, and note date and number of flats sowed for future reference.
  • Most seeds are viable for more than one year if stored in a dry place. I’ve had success with seeds up to three years old. If unsure, test plant just a few older seeds to see if they sprout.
Newly planted tomato seeds and their seed packets.

Newly planted tomato seeds and their seed packets.

When to sow seeds indoors: Seed packets recommended indoor sowing periods, usually listed as x to y weeks from last frost (find your hardiness zone and average frost dates). I tend to indoor-sow closer to lesser suggestion – if the packet suggests 6-8 weeks, I sow around 6 weeks. Smaller healthy seedlings transplant and adapt better than overly leggy seedlings.

The ever-critical hardening off: Indoor grown seedlings must be gradually acclimated to outdoor sunlight and conditions to prevent sun-scald and shock. This requires exposing them to outdoor sunlight and temperatures a little at a time. Shade, but bright light for the first 3 days, gradually increasing exposure to full sun a few hours every few days. Also protect seedlings from harsh winds. I prefer giving seedlings two weeks of hardening off before planting them into their permanent summer home.

Learn from your mistakes: Don’t beat yourself up. A mistake is not wasted if you learn from it. Everyone makes mistakes, even seasoned gardeners.

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3 comments for “Sowing seeds indoors

  1. Jim
    March 31, 2016 at 8:06 am

    Great tips! I’ve started seeds indoors, usually too early, and get terribly spindly leggy growth. By the time I get them outside it takes them a while to recover and start growing correctly. What type of grow light do you use? Nice article, thanks.

    • March 31, 2016 at 8:21 am

      Thanks, Jim. I use standard florescent shop lights. Would love to switch to LEDs but their price is still prohibitive.
      Keeping the lights as close to the top leaves of the seedlings as possible, and starting seeds at the later end of recommendations, are both key to growing non-spindly seedlings.

  2. April 3, 2016 at 7:10 pm

    Wonderful bit of information, I’m always trying to improve my germination rates.

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