Here’s what you need to know about when to start seeds indoors

don't sow these seeds indoors

Not all plants can or should be started from seed indoors. Some, like corn, simply don’t transplant well. Others, like sunflowers and cucumbers, grow so quickly that there’s little point in starting them early.

But for those plants that need a little extra time to give them the best chance of maturing during the growing season, it is essential to sow indoors . Here’s what you need to know about when to start seeds indoors.

Determine Whether Or Not To Sow Indoors

don't sow these seeds indoors

Some seeds shouldn’t be started indoors

Nearly all seed packets have sowing directions that tell you when to start your seeds. Look carefully to be sure you know whether to start your seeds directly in the garden or if they should be started indoors. Some seeds can be started either inside or outside , some should be started indoors only in certain USDA zones, and some should always be started indoors.


Check the seed packet carefully to see when to start seeds, and whether to start them indoors or outside.

Many vegetables will be direct sown in the garden, including:

  • Beans
  • Beets
  • Carrots
  • Corn
  • Cucumber
  • Kale
  • Lettuce
  • Melons
  • Peas
  • Spinach
  • Squash

Many annual flowers should also be started in the garden, such as:

  • Asters
  • Bachelor’s buttons
  • Calendula
  • Lavatera
  • Nasturtiums
  • Nigella
  • Sunflowers
  • Zinnia

In contrast, most perennial seeds will be started indoors.

Most herbs are grown by transplanting potted plants from the store or greenhouse. However, some herbs can be successfully grown from seed and some of those should be started indoors.

If your growing season is very short or you don’t have decent growing conditions, you may choose to sow some of the above vegetables and annuals indoors to give them a head start.

When to Sow Seeds Indoors

Hopefully, the back of the seed packet will give you a good idea of when to sow your seeds indoors. Usually, this will be described in terms of the number of weeks before the average last frost date.

To find your last expected frost date

Sometimes the seed packet will only tell you how many days it takes for the seeds to germinate. In those cases, add 6 weeks to the number of days as a good starting point.

And if there’s no information at all, go with 6 to 8 weeks before the last frost.

For additional local planting information, check your local Master Gardener Program or Cooperative Extension Service.

Why You Might Want to Start Your Seeds Earlier

There are a couple of reasons to start seeds earlier.

  1. If you’ll be growing your seeds in a cool area (below 70F), such as an unheated greenhouse, basement or garage, or cool room in your house, then expect seeds to take longer to germinate. They’ll likely grow more slowly too, so start the seeds a week or two earlier than planned.
  2. If you’ll be transplanting seedlings into a protected area that’s warmer than usual, such as a cold frame or greenhouse, under a row cover, or inside a “water wall,” then you can “cheat” a little by planting them outside before the last frost date. Just move your indoor sowing schedule up by a few weeks so the seedlings will be ready to transplant.

When to Start Your Seeds Later

Just as cold temperatures slow down germination and plant growth, warmer temperatures speed everything up. So if you’ll be growing seeds in a warm space (for example, a heated greenhouse or a warm room in your house that’s over 70F) then shorten your growing time by a week or two.

Vegetable Seeds to Start Indoors BEFORE Last Frost

The tables below give approximate seed starting dates. These should be fairly accurate for most areas of the country and most vegetable varieties, but check the seed packet for specific instructions as some cultivars can have different requirements.