September marks an important transition for the garden, signaling the start of fall gardening, often referred to as succession planting. This strategy uses decreasing air temperatures and still-warm soil to establish a second round of crops. Planting now ensures a final harvest before the first hard frost or establishes hardy plants that survive the winter for an earlier spring crop. The cooler weather reduces pressure from summer pests and slows bolting in leafy greens, resulting in sweeter, more tender vegetables.
Cool-Weather Vegetables for Quick Fall Harvest
September is an excellent time to sow seeds for a rapid return, focusing on varieties with short days to maturity. Gardeners should calculate planting dates by counting backward from the average first frost date, adding a couple of weeks to account for reduced autumn sunlight. This ensures crops reach a usable size before freezing temperatures arrive, especially those that cannot tolerate a hard freeze.
Leafy greens are among the fastest and most reliable fall crops, thriving as the days cool. Arugula, a peppery mustard green, can be ready for a first harvest in as little as 20 to 30 days from seeding, making it one of the quickest options. Spinach and various loose-leaf lettuce varieties typically require 40 to 50 days to mature, and their flavor often improves after exposure to a light frost.
The brassica family offers several fast-maturing choices, including quick-growing varieties of Napa cabbage or broccoli rabe, which can be ready in about 45 to 60 days. These plants prefer the mild temperatures of fall, which discourages the premature flowering that heat can induce. Kale and Swiss chard are exceptionally frost-tolerant and can continue to produce leaves well into the late fall and early winter.
Root vegetables also benefit from a September sowing, with radishes often harvestable in just three to four weeks. Other root crops like beets and turnips take longer, maturing in 45 to 65 days, but the cooling soil helps concentrate their sugars, enhancing their flavor. The greens of both beets and turnips are also edible and provide a secondary harvest.
Crops Planted in September for Spring and Early Summer Harvest
Vegetables planted in September are not always for immediate consumption but establish a strong root system before the ground freezes. These crops require a period of cold dormancy, known as vernalization, to properly develop and produce a harvest the following year. Planting them now allows for an earlier yield than if they were planted in the spring.
Garlic is the most notable example of an overwintering crop, as the cloves must experience several weeks of temperatures below 40°F to stimulate bulb division and growth. Planting individual cloves in September or early October ensures they form a strong root base before winter, leading to larger and earlier bulbs the following summer. Certain onion sets, specifically those marked for “fall planting,” should also be placed in the ground now to establish themselves.
Beyond alliums, cold-hardy greens are planted in September for overwintering. Varieties like corn salad (mache or lamb’s lettuce) and winter-hardy kale can survive under a layer of snow or protective cover. These greens slow their growth during the coldest months but are among the first to resume active growth in early spring, providing a harvest weeks ahead of spring-sown crops.
Carrots and parsnips can also be planted in September; their roots remain viable underground even if their tops die back in winter. Covering them with a thick layer of mulch keeps the soil from freezing solid, allowing them to be harvested throughout the winter or dug up immediately after the spring thaw. This cold exposure makes the root vegetables sweeter as they convert starches into sugars as a natural antifreeze mechanism.
Optimizing Conditions for Late Season Planting
Successful September planting relies on preparing the garden environment to support growth during the shortening days and cooling temperatures. The soil is the first priority, as it is often depleted and compacted after a summer of production. Incorporating fresh organic matter, such as compost, is necessary to replenish nutrients and improve soil structure for new seedlings.
While the air temperature cools, the soil often remains warm enough to encourage rapid germination, which is an advantage over chilly spring planting. However, this lingering warmth, combined with potentially dry conditions, necessitates consistent watering, especially immediately after seeding. Watering deeply but less frequently encourages the development of strong, deep root systems that better withstand eventual cold.
Protecting young plants from early frosts and extending the harvest window requires the use of season extension techniques. Simple structures like cloches, row covers, or cold frames are useful for this purpose. Row covers, made of thin, lightweight fabric, can provide a temperature increase of several degrees, safeguarding foliage from light frost while still allowing light and water penetration.
A cold frame, which is essentially a bottomless box with a transparent lid, traps solar energy and shields plants from wind and heavy precipitation. Applying a thick layer of straw or shredded leaves as mulch around overwintering root crops, such as carrots or parsnips, helps insulate the soil. This insulation prevents the ground from undergoing repeated freeze-thaw cycles that can damage the root structures.