As we bask in the long, hot days of high summer the cooler weather of fall and winter still seems a long way off. But if you're escaping the heat by strolling in an air conditioned shopping mall you're bound to see a sure reminder of the coming seasonal change -- the bathing suits are on sale! This means that it will soon be time not only to start thinking about your new fall wardrobe, but also to start getting ready for a late season harvest in the vegetable garden. If you'd like to continue to enjoy a bounty of homegrown veggies into the fall months (or even winter, depending on your climate and the protection you give your crops), planning and planting starts in July and August.
Cool season crops are naturals for fall harvest. Cole crops, greens, and root crops are all good choices. And some crops, such as kale and Brussels sprouts actually taste sweeter when harvested late in the season after they have been touched by frost. In areas with mild winters, like southern California, the Gulf Coast, and warm parts of the Southwest, you may even be able to grow cold tolerant crops throughout the winter.
So what's the secret to fall gardening? Planning ahead! As we mentioned, in order to reap a fall harvest, in most parts of the country you need to think about planting well before autumn arrives. You may be busy picking beans, corn, and tomatoes, but take some time out to plant seeds of crops so they will be ready for harvest in the fall. Crops that take longer to mature, like cole crops and root crops, will need to be planted earlier than fast maturing crops like spinach and lettuce. And you need to keep the expected date of your first fall frost in mind. Gardeners in shorter season areas will need to get seeds and transplants out earlier in the summer than those in areas where frost holds off until late fall.
Cold hardy kale makes a great addition to hearty soups and casseroles.
Fall Planting Formula
To figure out what to start when in your climate, begin by figuring out the date of the first expected killing fall frost. While tender crops like beans and basil will be killed by light frost (below 32 degrees F), many cool season crops survive until hard frost, when temperatures dip below 28 degrees F. Especially hardy kale, cabbage, collards, and Brussels sprouts can withstand hard frosts, but will be killed when temperatures get down to 20 degrees F. or lower. To figure out when these temperatures arrive in your area, check with your local Extension Service or check out information available online from NOAA.
Next note the days to maturity (DTM) for the particular crop and variety you plan to grow. (Check the seed packet or catalog info to see if the days to maturity are from direct seeding or transplanting. If the DTM are from transplant to harvest, add another 2-4 weeks if you are growing your own transplants from seed.) When possible, choose varieties with the shortest DTM for fall harvests.
Add to this the length of the average harvest period. Then add in a fall factor of about 14 days. The fall factor takes into account the slower growth of plants as the days get shorter and cooler in late summer and fall.
Add up the days to maturity (including days from seeding to transplant, if needed), the harvest period, and the fall factor. Then count back this number of days from the fall frost date to arrive at your planting date. If you plan to protect your crops with a cold frame, cloche, or low tunnel, you can plant 2-4 weeks later than you would for unprotected crops.
If you're trying to decide how late in the season you can squeeze in one last planting of a frost-tender crop like beans or basil, add an extra two weeks to the formula to make sure your plants mature in plenty of time to allow for a reasonable harvest period before light frost kills the plants.
The beauty of this formula is that it allows you to tailor your planting times not only to your climate and the kind of vegetables you're growing, but to the specific varieties you choose. For example, a quick perusal of seed catalogs showed me varieties of broccoli suitable for fall growing with a days to maturity ranging from 48 to 90 days; the formula will take these varietal differences into account in relation to the planting date.
But if you'd like to have someone else do the figuring, take advantage of Johnny's Selected Seeds online Fall Harvest Planting Calculator. Enter your average first frost date and the calculator will tell you when to plant a wide variety of crops for fall harvest. It won't be as targeted to the DTM of specific varieties, but it's fast and easy!
Cold Tolerant Examples
Where I live in Vermont, a light frost (32 degrees) usually hits around October 1. Harder frost (below 28 degrees) usually holds off until around October 10, and 24 degree temperatures come about October 25 on average. Let's say I want to grow 'Red Russian' kale to full size without protection this fall. Since this hardy plant will weather temperatures down to 20 degrees or lower, I'll use October 25 as my frost date. The seed packet lists 50 days to maturity from seeding. To this I'll add a 14 day harvest period and a 14 day fall factor, for a total of 78 days. Counting back 78 days from October 25 gives me a planting date of August 8. So I'll plan on getting my kale seeds in the ground sometime in the first couple of weeks of August in order to have a nice, long harvest period. If I decide to protect my kale by planting in a cold frame or covering plants in a low tunnel, I can add about a month to this schedule, planting as late as mid-September.
Broccoli is another good fall crop, but one that's not as cold hardy as kale. So I'll use October 10, my average date of 28 degree temperatures, in the formula. 'De Cicco' is an heirloom variety with excellent flavor that matures from transplanting in just 48 days. I'll add another 28 days to this number to allow for starting plants from seed. Tacking on my 14 day fall factor and 14 day harvest period brings me to 104 days. Counting back I arrive at June 29, meaning I need to be starting my broccoli seeds at the end of June or the beginning of July. If instead I buy started transplants from a garden store, I can wait until around August 1 to get them in the ground. And, again, if I plan to give the broccoli plants some protection, I can delay my planting time by 2 or 3 weeks.
Kohlrabi is an unusual and tasty member of the cabbage family that is well-suited to fall growing.
Crops for Fall Harvest
Salad Greens: Crops such as lettuce, spinach, arugula, endive, mache, and mesclun are great for fall harvest because they mature quickly, grow well when the weather is cool, and are less likely to bolt or go to seed than spring planted crops. Both spinach and lettuce germinate poorly in warm soil (above 60 degrees) so if you are starting plants in late summer, cover beds with shade cloth after planting or start seeds indoors and transplant.
Hardy Greens: Fall is a great time to grow these nutritious crops. Kale, collards, Swiss chard, mustard greens, and bok choy all thrive in cooler weather. A few frosts will even sweeten the taste of your kale. If you are growing it as ″baby″ greens, you can sow seeds just a few weeks before frost. Some varieties of kale, such as 'Siberian', are especially cold tolerant and can be harvested even after snow covers the ground.
Cole Crops: Like kale, Brussels sprouts taste best after sweetened by a light frost. But they take a long time to mature, so be sure to get them on your planting schedule in early to midsummer. Other cabbage family members that are suited to fall harvest include broccoli, cabbage, Chinese cabbage (napa), kohlrabi, and cauliflower.
Root Crops: Beets, carrots, turnips, and radishes are all suitable for fall harvests. Root crops that mature in the cooler weather of fall will be sweet and mild. In the warmest areas, you can grow these crops right through the winter months.
Peas: These grow well in the cooler weather of fall, but can be damaged by frost, especially the developing pods. So try to time your fall pea sowing so plants mature a week or two before the fall frost date, and be prepared to cover plants if an early frost threatens. Keep the seed bed well watered to ensure good germination.
Herbs: Dill, cilantro, and chervil all grow well in cool fall weather and unlike spring crops, are less likely to bolt or go to seed quickly. Make successive sowings of these crops every few weeks from midsummer up until about 6 weeks before your frost date. In mild winter areas, these herbs can be harvested through the winter months.
Leeks and Onions: Sow seeds of scallions or bunching onions about 8 to 10 weeks before your fall frost date; then begin harvesting when plants reach about 6 inches tall. In mild winter parts of the country, leek seeds may be started in late summer or early fall for harvest in the winter and spring. In cold winter areas leeks may be harvested in the fall, but because they take a long time to mature they are planted in spring.