Seed Starting for Fall Crops

Although we’re just picking our first tomatoes, it’s already time to think about starting seeds for fall harvests. Starting seeds in mid-July is largely the same as starting seeds in early spring, but keep in mind:

  • Many homes are a little warmer now with the summer heat, so seeds sprout much more quickly now than they do in early spring!
  • Sunlight coming through windows is a little brighter, so grow lights aren’t as necessary (but still great if you have them).
  • Seeds can also be directly sown in the garden, so you don’t have to set up anything indoors.

What can be planted now? 

In Chicagoland, here’s what cool-weather crops can be planted now to have a harvest before the first frost:

These should be planted directly in garden soil now or in the next few weeks:

  • beets, radishes, turnips and most varieties of carrots

Here’s what should be planted directly in garden soil in a few weeks (anywhere from mid-August to early September):

  • radishes, spinach, arugula, lettuce

These can be started indoors now on a very sunny windowsill,  under grow lights, or directly in garden soil:

  • broccoli, cauliflower, rapini, bok choy, mustard greens, kale, swiss chard, cilantro

Once these seedlings have been growing indoors for a few weeks, plant them outside in the garden if they weren’t already directly seeded. Be sure to harden off so they can adjust to brighter light and fluctuating temperatures. If you don’t have space in your garden yet, you can “pot up” the seedlings to slightly larger pots, but be sure to add a little fertilizer when doing so. When space opens up in your garden, go ahead and transplant, as long as it’s by mid-August.

How to I know if it’s too late to plant?

Check out the seed packet for the “days to maturity”. Here’s an important cool-weather seed-starting tip: as the hours of daylight get shorter as we approach autumn, you will need to add about two weeks to the “days to maturity” to accurately predict when your plants will be ready to harvest. This should be kept in mind so you start seeds early enough that they’ll be ready to harvest before the first frost date. In Chicagoland, this is typically between the third week of October and early November.

From today, there are about 96 days before the first expected frost, which averages around October 24th. Let’s take a look at some of our seed packets.

This 'Mammoth Red Rock' Cabbage is 98 days from transplant to harvest.

This ‘Mammoth Red Rock’ Cabbage is 98 days from transplant to harvest.

Unfortunately, if we start seeds for this cabbage today, it will not be ready for harvest it in time for the first frost. How come? Since we are starting seeds mid-summer, and the plant will be maturing as the days grow shorter, we need to add 14 days (two weeks) to the expected harvest date (98 days from transplant), putting it well into November. To harvest it in time, seeds should have been started in late June or early July, and then the cabbage seedlings transplanted to the garden last week.

'Five Color Silverbeet', known by many as Rainbow Chard.

‘Five Color Silverbeet’, known by many as Rainbow Chard.

This swiss chard is 50-60 days to harvest. It can be started indoors, or direct-seeded in the garden any time between now and mid-August. If started a little later, it will be “salad size” by October, which is what some prefer!

How do I know if it’s too early to plant?

Some seeds, such as lettuce and spinach, prefer to sprout when the weather is a little cooler. That’s why it’s a good idea to wait a little more toward the end of the summer to plant directly in the garden.

How do I start seeds directly in the garden?

Check out this video for tips on starting seeds directly in the garden.

Why do my summer-planted radishes and arugula bolt before producing a harvestable crop? 

Plants can bolt (go to seed) when they are physiologically ready to reproduce (after growing to maturity in the spring, for example) and when they are water- or heat- stressed. To keep the arugula, spinach, lettuce, and radishes from bolting before they grow to a harvestable size when planting in mid-late summer, keep well-watered and partially shaded.

How do I start seeds indoors?

Check out our previous post on seed starting.