How Late Can You Plant the Seeds for Vegetables?

Kale can be planted in early spring, but is sometimes planted between midsummer and late fall for winter harvesting.

There is not a single month of the calendar year when vegetable seeds cannot be planted, either indoors under lights or by direct sowing outdoors under cover. The trick to knowing how late can you plant the seeds for vegetables outside, is simply knowing what vegetables you can plant, and when you can plant them where you live.

Local Climate

Knowing your general location is necessary to use the USDA hardiness zone map.

It is necessary to know what U.S. Department of Agriculture hardiness zone you are in. Once you know this information, look at the types of seeds you wish to plant and see what their minimum temperature requirements are. There are a total of 11 USDA hardiness zones, which are further broken down into "a" and "b" zones except for USDA hardiness zones 1 and 11. Each full zone varies by 10 degrees Fahrenheit, while each "a" and "b" zone vary by 5 degrees Fahrenheit with the "b" zones being warmer.

There are multiple USDA hardiness zones in every state. For example, in California, there are six USDA hardiness zones, which include USDA hardiness zones 5, 6, 7, 8, 9 and 10.

Cool Season Crops

Radish sown in late fall is harvested into the early winter months.

Seeds of many cool season crops, such as lettuce, are planted year-round in an area with a minimum temperature of -20 degrees Fahrenheit, or USDA hardiness zones 5 and warmer.

Other cool season crops that can be re-planted in the fall or early winter and will germinate the following spring include kale, spinach, radish, turnips and various varieties of mustard. These crops may also be planted in mid-summer, for fall harvesting.

Warm Weather Crops

Cherry tomatoes, especially heirloom varieties, often reseed themselves from year to year.

Some warm weather crops are planted outdoors year-round. The use of a cold frame, which is a box-like structure with four sides and a glass or plastic top, can protect these crops from cool weather and frost. Leaving a sprinkler running all night when frost threatens will also help protect warm weather crops from frost damage.

Many warm weather crops will re-seed if left in the garden over the winter. These crops include amaranth, cherry tomatoes, corn and pumpkin.

References

• The United States National Arboretum: USDA Plant Hardiness Zone Map
• University of Minnesota: Planting Vegetables in Midsummer for Fall Harvest
• University of New Hampshire: Planning a Winter Vegetable Garden
• "The Complete Idiot's Guide to Year-Round Gardening"; Delilah Smittle and Sheri Ann Richerson; 2010

Resources

• When To Plant Vegetable Seeds