Indoor Seed-Starting Tips

There’s a lot of information out there about starting seeds indoors. While there are definitely better ways to grow seeds, a certain amount of fudging is acceptable. Here in our house, we’ve had our share of seedlings that came home in Dixie cups from elementary school and fared just fine.

Still, if you want to boost your success and the health of your plants, take a look at these tips. By growing from seed, you’ll have a greater selection of varieties from which to choose.

1) Use clean, well-draining containers, such as recycled cell packs from last season. Soak IMG_20180224_110315670.jpgthem in a 10% bleach solution for 10 minutes.

2) Don’t use garden soil: it’s not sterile, it’s too dense for tender seedlings, and won’t drain well.

This seed-starting mix with peat as its main ingredient is relatively cheap (around $5), OMRI-listed, and easy to find at Home Depot.

Personally I don’t like the little peat discs that puff up when soaked in water because it’s too difficult to control their moisture  content and they usually end up quite wet.

You want to moisten your soil until it’s damp and holds together, not drench it until it’s dripping.

3) About those seeds

  • At PPCG, you do not have to select organic seeds to grow organically. Choose them if you don’t mind spending a little extra money to support organic production of seeds. Usually you will find a wider selection of non-organic varieties.
  • Follow the directions on the seed package with regard to how deep to plant the seeds.  Some seeds need light to germinate and should simply be gently pressed onto the top of the soil; others need to be planted deeper.
  • Plant 2-3 seeds per cell (or whatever kind of container you’re using). After they sprout, choose the best seedling in each cell and clip the rest. (Don’t pull out the extras to avoid disrupting roots.)
  • If you’re carrying seeds over from last year’s stash, expect a lower germination rate. Here’s a way to test your seed viability.
  • For some crops, direct-sowing in the garden is better, either because they don’t transplant well or they grow quickly (and often early) enough that you don’t need to start them indoors. These include: beans, beets, carrots, cucumbers, peas, radishes, salad greens, squash, sweet corn, and turnips.

4) Seeds like a little bit of warmth to germinate. Seed-starting warming mats help along the germination process. Or try a warm spot in your house, such as the top of your refrigerator, but remember to keep a check on them.

5) Keep them moist, too. If you stick them in a bag like this, they should be all set for a IMG_20180224_114143841.jpgfew days.

6) But once they’ve sprouted, they like cooler temps in the 60s. Get them under the lights and take them out of plastic right away.

If your seedlings start to get tall and spindly, they might be too warm or not have enough light.

Sixteen hours is best, which is why I did invest in a grow light.

Prop them up so they’re right under the light, about 3 or 4 inches away. Keep adjusting them so that as they grow, the leaves do not touch the light.

Here’s another trick to try: cover sheets of cardboard with aluminum foil and position them to reflect light from a window, etc. back onto your plants.

7) And finally, if all of this sounds like too much of a bother, skip it all and watch for the great plant sales we have in our area.

Playing the Odds with Frost Dates

Here in Massachusetts, I’ve often gone by the rough guideline of waiting until Memorial Day weekend to put out all but my cold-tolerant plants. It’s not a terrible guideline, but the date of Memorial Day does vary from year to year, from as early as May 25 to as late as May 31. It’s also too late for certain cool weather crops and can unnecessarily cut short your garden’s growing season.

Official frost dates are often given as a single number, such as this date given on the Old Farmer’s Almanac website.

farmers alm frost date

Here, the frost date is listed as April 16, which is quite a difference from the Memorial Day guideline.

A few things can be noted about this chart. (1) It uses weather data from South Weymouth.  And (2) it calculates a spring frost date at which there is still a 50% chance of a later spring frost. (Update: Old Farmer’s Almanac now uses 30% odds, which moves the frost date back to April 22.)

How lucky are you feeling at 50-50 odds? (Or the updated 30% risk of frost?)

I’d definitely feel okay about putting out kale at this time, which says nothing about my feelings toward kale. (It’s all right.) Kale can take the cold weather.

For a better sense of frost dates, I like this chart from (Click here to see the full chart; excerpt is below.)

Temp (in Deg F) 10% 50% 90%
Last 16 Mar 25 Mar 10 Feb 24
Last 20 Mar 31 Mar 19 Mar 8
Last 24 Apr 12 Mar 30 Mar 17
Last 28 Apr 27 Apr 15 Apr 4
Last 32 May 15 Apr 30 Apr 16
Last 36 May 25 May 13 May 1

According to this chart, there’s only a 10% risk that temperatures will drop below 32 degrees F after May 15. Now we’re getting closer to the old rule of thumb. But note that there’s still a 10% risk of 36 degree weather after May 25, which could set back members of the nightshade family (e.g., tomatoes, potatoes, eggplant, peppers). Warm weather crops don’t just need frost protection, but also warmer growing conditions to fully thrive. (Side Note: For a number of reasons, your garden may experience colder temperatures than those measured at local weather stations. Using the dates associated with 36 degrees gives you a little bit of insulation from frost.)

Click here if you’d like to see another chart, but don’t get too bogged down in the numbers. We’re looking for guidelines based on data, not one proven date.

Bottom line? “Frost date” is better expressed as a range of dates and probabilities.

Also think about…

  • How cold-tolerant your plants are.
  • How much risk you can handle and how sad you would feel if you froze that one special tomato plant variety you can’t get anywhere else.
  • How willing you are to take some extra measures to protect your plants if a frost bogey threatens crops in late spring/early fall.
  • How long you can hold your young plants in their containers. They’ll take some time to recover if they start to get pot bound before you put them out, which is another kind of risk.