There's no need to tuck your garden in at the first sign of autumn. Many vegetable varieties thrive in fall's cool weather and ample rains. Extend your garden season by selecting cold-tolerant vegetables planted in mid- to late summer for fall harvest, or plant swift-growing salad crops in early autumn for fresh eating until hard winter frosts arrive.
Cole crops are plants in the Cruciferae, or mustard family, such as broccoli, Brussels sprouts, collards, cabbage, cauliflower, turnips and kohlrabi. According to the Texas A&M University Extension, most cole crops grow best at temperatures between 60 and 70 degrees Fahrenheit, and they can withstand light frosts, which makes them ideal for autumn growing in most parts of the United States. Texas A&M recommends planting cole crops like cabbage, broccoli and Brussels sprouts in late summer, and planting fast-growing Cruciferae like baby turnips and kale through September for harvest throughout autumn.
Many root vegetables planted mid- to late summer will continue growing through the autumn. The flavor of root vegetables is improved by a touch of frost, which converts their starches to sugar. These sweet crops can be harvested until the ground is frozen too solid to dig them out. Oregon State University Extension recommends Winterkeeper beets, Bolero or Merida carrots, All Season's White Long radish, Cobham Marrow parsnips and Purple Top White Globe turnips for autumn growing. Mid-summer plantings will yield large root vegetables suitable for winter storage, but plantings as late as mid-September in most areas will produce baby-sized (2 inches in diameter or less) root vegetables perfect for autumn harvesting, and roasting or boiling whole.
Fast-growing greens can be planted until about six to eight weeks before the average first frost date, and harvested by picking off outer leaves and letting the inner leaves grow until the onslaught of hard winter frosts. The University of California Davis Master Gardener Program suggests loose-leaf, cos, butterhead and crisp head lettuces for autumn growing. Kale, spinach and Swiss chard can also be planted from mid-summer to early fall, and harvested when the leaves are less than 4 inches long for fresh salad use, or left to grow larger for cooking purposes.
The most cold-hardy greens can be planted until the ground freezes, including mache, arugula, radicchio, frizzy endive and Italian dandelion. These winter-hardy salad vegetables will grow through autumn and, in areas that do not experience a hard winter freeze, may continue producing right into spring.