Sow What (and Where?): a seed starting primer

It’s spring!  And that means it’s time to sow seeds.

organic tomato seedlings in flats

organic tomato seedlings in flats

If you live in a northern state like Vermont, it also means there’s still snow on the ground.  So we sow indoors.

Each crop has it’s own specifications when it comes to seeding: number of days to emergence, soil temperature, light, etc.  Keeping it all straight can feel like an entire spreadsheet is required (really, it does help!).  While there are some helpful cheat-sheets on when to start each crop, there’s sometimes more nuance than a spreadsheet can handle.

A friend recently sent me this question about seeding:

Q: I recently moved to a place with a beautiful greenhouse. Some of my seeds (like eggplant) say that starting outdoors isn’t recommended, but is starting directly in the earth in the greenhouse basically the same as starting indoors? In other words, can I start “indoors only” seeds right in the ground in the greenhouse if the soil temp. is ok?

Eggplant, along with other warm-season crops like tomatoes and peppers, are typically started inside and transplanted outside when the temperatures are suitable.  There are a few specific reasons to start these crops inside:

  • In northern latitudes, where the growing season is relatively short and cool, the head-start that comes from sowing indoors ensures a harvest before the season ends.
  • Some crops can germinate in cool soil, but many require soil temperatures of at least 65º or higher.  Growing seedlings indoors allows you to control the soil temperature even when it’s cool outside.
  • Starting indoors makes consistent watering easier.
  • Starting with weed seed-free potting soil indoors ensures your seedlings won’t have to compete for nutrients.

Soil Temperature Matters

The ideal soil temperature for germination depends on the crop.  Too cold and too hot can both inhibit germination.

At Good Heart Farmstead, our stand-by book for all things seed-starting is Nancy Bubel’s The New Seed-Starters Handbook.  Bubel includes helpful charts laying out ideal soil temperatures and how quickly a seed will emerge at specific temperatures.

Eggplant in particular requires a minimum soil temperature of 68º, but will germinate much faster at 86º (a whole eight days faster, in fact!).  Tomatoes will germinate in soil at 59º but will take 13 days to emerge, and are much happier (and speedier) at 77º.

Since we start many crops in the same greenhouse at Good Heart, we aim for an average 70º, with sunny days heating up the space more, and nights dipping down to 65º

What to sow into?

There are many different types and sizes of trays or pots to start your seeds in.  At Good Heart, we mainly use soil blocks, which skip the plastic altogether.  If you’re starting out on a tight budget, though, it may be easier to find pots and plastic trays at your local garden center.  Recycled pots are relatively easy to find by posting on a community forum or checking your local transfer station come spring.  If you want to get really thrifty start seeds in empty egg cartons.

The soil you seed into is more important than the type of pot you use.  Be sure to use an organic potting soil.  Organic soils will be free of fungicides or other chemical additives, and will give your seeds the best start.  We use Vermont Compost Company’s Fort V potting soil, which works great for soil blocks and plastic trays alike.

Now back to the main question: is it okay to sow “indoor-only” seeds directly into a greenhouse bed?

The answer is yes.

Whether you’re starting indoors in flats, pots, soil blocks, or in a bed, so long as you have consistent temperature and moisture, sow away!

sowing seeds in the greenhouse

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