Sunday, March 3, 2013

Indoor Seed Starting

I try to grow nearly all of our our plants by seed. Many gardeners will rely on buying transplants, either from a lack of planning ahead, or else due to the misperception that indoor seed starting is difficult. As an urban gardener (and apartment dweller), I know that space is a valid excuse, although I still make do with my windowsills.

Is fancy equipment necessary? Definitely not. I've never used a grow light in my apartment, as most plants do pretty well with natural light. The school gardens that I run all have grow lights in the classrooms, and they do indeed speed up the process and make it even easier, but still not absolutely required. A little more care is needed without grow lights.

What and when do we start seeds? This varies by variety, and most seed packets will have instructions. In New York City, I tend to start many of the nightshades, cabbages and other warm-weather transplants around March 1, to be planted 8 to 10 weeks later (by early to mid-May). Wait until early to mid-April to start cucumbers and squash, as they are transplanted as young seedlings, otherwise risk being too stringy and delicate. Beans could also be started indoors a few weeks earlier, but I always direct sow them.


Water tight trays. You can purchase a cheap seed starting tray system, or you can reuse some plastic household items, such as the take-out Tupperware containers or plastic salad containers.

Clear lid. These would be included in a seed staring tray system. The reusable containers can be covered with another clear container or plastic wrap. The salad containers are easiest because identical containers can be used for both the tray and the top.
Jiffy Disks

Jiffy disks or earth plugs. These are the easiest things to use, eliminating the mess and effort of mixing soil and filling little pots or cells.

Or, rather than using the above, you can purchase small peat pots or seed starting cells, and add seed starting medium, coconut choir or a fine and spongy soil. This is the most cost effective way for larger seed starting operations, and this is what we use in most classrooms.


  • If using disks, put in bowl or tray, and fill with warm water and wait for them to expand.
  • Place disks, plugs or filled cells/pots in tray.
  • Add seeds, cover (as per instructions)
    • if using disks or plugs, just push the seeds in the required depth, or sprinkle with fine soil or vermiculite.
  • Place plastic lid on top.
  • Put in sunny window
  • Keep the tray damp but not swamped. Add water before it dries out, watering from bottom, not directly onto seeds.
  • After seedlings germinate, remove lid.
  • As seedlings begin to outgrow their space, you may need to transplant them to a larger pot...if they are not yet ready to plant outside. Hopefully this step can be avoided.
  • Harden off seedlings a week or two before they will be planted
    • seedlings will be shocked when planted outside, so need to be gradually acclimated to wind, sun and varying temperatures. Most importantly, planting in the ground (or large container) can cause a large amount of shock that can prove fatal for many seedlings.
    • If possible, you can bring seed trays to a sheltered, shady are for a few hours per day, gradually building up the amount of exposure. This is a lot of work so I only encourage people to do this if it's convenient.
    • More practical and realistic, you can leave them outside, away from too much direct sun and wind. Just keep seedlings monitored, and bring them in during any extreme weather changes (storms, early heat waves, late cold spells, etc.), but otherwise just leave them be, and after a week or two they will be ready for the ground.

A Few More Steps to Make Seed Starting a Success

Here are a few extra steps that may come in handy...

  • Sterilize growing trays
    • With larger production greenhouses or farms, it is important to prevent blight, molds or any pathogens that can destroy entire crops. Thus sterilization is recommended.
    • A small school or home operation usually doesn't need this; I've been only rinsing my trays for years, and no problems.

    • Option 1. Bleach bath (1:50 bleach:water) in warm water.
    • Option 2. Run through dishwasher

  • Pre-germination
    • Some types of plants are tougher to start and take longer to germinate. Even within the same species, certain heirloom varieties, or also older seeds, take longer to germinate. Others are prone to get stuck in their stubborn seed coats. Pre-germination speeds up the initial germination, and then sprouts will be planted in seed trays. I usually pre-germinate all nightshades, squash/cucumbers, Moon Flowers, sorghum, and others.
    • Step 1: Soak seeds over night.
    • Step 2: Place a bunch of seeds in a damp paper towel, but make sure they're spaced an inch or so apart.

    • Step 3: Place paper towel in a ziplock or tupperware, and seal. I usually fold the towel gently so it fits. Place in a dark, warm area.
    • Step 4: Check every few days. It's important to transplant sprouts soon after they sprout, and also find and remove any moldy seeds.
    • Step 5: Transplant to the growing medium. I usually use a toothpick or chopstick to make a small hole and bury just covering the roots but not stem. Don't be intimidated in handling delicate seedlings, but just do everything gentle, and if one breaks, discard and plant another. The pale seedling will turn green after a few days of light. 


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