When to Plant Kale

Spring planting

Kale tolerates cold far better than heat, so in spring the goal is to start early enough for plants to produce before temperatures stay above about 75°F. Utah State University Extension puts transplants in the garden 4 to 5 weeks before the average last frost and direct-sows seed on the same day. Young plants are not seriously harmed down to about 25°F, so a late frost after planting is not a reason to panic.

If you grow your own transplants, start them indoors 5 to 6 weeks before that planting date. That is how long they need to reach 4 to 6 true leaves and a solid root system. Transplants give you an earlier harvest. Many more varieties are sold as seed than as plants, which is why UConn’s Home & Garden Education Center notes that spring kale is often direct-sown.

Seed is slow in cold ground. UConn gives 5 to 17 days to sprout, depending on soil temperature, so seed sown into near-freezing soil will sit for a while before anything shows.

The dates for your zone above give the spring windows for indoor starts, transplanting and direct sowing.

Fall planting

In most of the country fall is the better kale season, because the plants mature in cool weather and frost sweetens the leaves. There are three ways to time it, and they land in roughly the same place:

• Utah State: choose an early variety and plant 50 to 75 days before the date you want to harvest, aiming for a harvest about 2 to 3 weeks after the first fall frost.
• Maryland Extension: take the variety’s days to maturity, add 10 to 14 days to allow for slower growth as days shorten, and sow that many days before the first frost.
• Illinois Extension: sow very hardy crops such as kale at least 8 weeks before the average first frost.

Nebraska Extension’s version of the formula also counts the weeks needed to raise transplants and the length of the harvest you want, so add those if you are starting seedlings yourself.

Late-summer sowing means hot, dry soil. Purdue and Nebraska both suggest a light mulch of compost, vermiculite or potting soil over the seed row to stop crusting, slightly deeper sowing than in spring, and frequent light watering until seedlings are up. UConn sidesteps the problem by starting fall kale in six-packs in early August in Connecticut and transplanting the seedlings.

How late can you leave it?

Once established, kale is one of the last crops standing. Maryland Extension puts its limit at about 15 to 20°F, and Nebraska lists hardy crops including kale as surviving several frosts until temperatures drop near 20°F. A row cover, cold frame or sheltered spot stretches the harvest well into fall in the mid-Atlantic, and the University of Arizona notes many gardeners simply leave kale in the garden all winter.

Warm-winter regions

Where frost is rare, plant in fall and pick through winter into early spring. Summer is the off-season there, not winter.

• Florida: UF/IFAS schedules kale from early fall through winter in all three regions of the state, with South Florida’s window ending a little sooner.
• Phoenix low desert: the Maricopa County calendar runs kale sowings from late summer through early winter. It also advises holding fall plantings until whitefly numbers drop with cooler weather.
• Lower Rio Grande Valley, Texas: Texas A&M treats kale like broccoli. Start seed in flats from early fall into early winter, and set plants out about 3 to 4 weeks later. Avoid transplanting before early October; plants do best set out from mid-October on.

The higher, colder parts of Arizona behave differently. In Prescott (zone 7b), the Yavapai County extension agent reports growing kale year-round, with germination and growth slowing once winter sets in.