In addition, some vegetables don't like to be transplanted. These vegetables include most root crops, like carrots, beets, and turnips. They're cold-hardy vegetables, so you can direct seed them pretty early anyway. Crops like corn, beans, and peas are also finicky about transplanting and grow better when you direct-seed.
Summer squash like zucchini can go either way; the growth is so rapid that many people just plant the seeds outdoors after the soil warms up—but you can buy them as starter plants if you like.
The soil temperature is different than the growing temperature. That is why many cole crops are started indoors. For straight to the ground planting soil temperature should be:
- 40° F or warmer: Lettuce, kale, peas, spinach.
- 50° F or warmer: Onions, leeks, turnips, Swiss chard.
- 60° F or warmer: Broccoli, cabbage, cauliflower, carrots, beans, beets.
- 70° F or warmer: Tomatoes, squash, corn, cucumbers, melons, peppers.
You can take soil temperature with any glass bulb thermometer. Use a screwdriver to make a pilot hole. Take your measurement at the recommended planting depth for your seed. If you’re measuring for a mixed garden, check at least 5-6 inches deep. Take a reading in the morning and late afternoon, then average the two numbers. If you’re seeding a lawn, take readings on all four sides of your house, since some areas warm more quickly than others.
Beans, beets, broccoli, brussel sprouts, spinach and other cole crops can be started from seed in August if you'd like fresh vegetables in the fall. But, we suggest purchasing the seed now as varieties can get hard to find in late summer.
One of the most common reasons a seed fails to sprout is sowing too deeply; a seed has only enough food within itself for a limited period of growth and a tiny seed sown too deeply soon expends that energy and dies before it can reach the surface. Another common cause is watering. Seeds need a supply of moisture and air in the soil around them. Keeping the soil too wet drives out the air and the seed quickly rots, whereas insufficient water causes the tender seedling to dry out and die.
Hey, if it was too easy, everybody would do it.