Gardening: Planting for a fall vegetable crop

So, it’s almost the end of June and it hasn’t even gotten hot yet. But even so, you’ve been enjoying your homegrown vegetables, maybe peas, lettuce, and spinach while looking forward to green beans, zucchini, peppers, and tomatoes later in the summer. If you’re still gung-ho about growing your own vegetables to eat, surprisingly, now is the time to start thinking about planting in the empty spaces so that you can have a fall crop of vegetables. I know it’s hard to think about fall crops before you’ve even harvested your first tomato, but but planting fall crops is a great way to maximize space and use up any leftover seeds. If you’ve only ever gardened during the summer, planning and planting for a fall harvest will be a tasty adventure.

Take advantage of planting in the spaces that are now empty (or soon will be) from vegetables you have already harvested. Clean out any remaining debris, fertilize to replenish nutrients if necessary, and then you can plant your fall crops. Many retailers still have seed packets available for sale.

By Susan Perry
Colorado State University Extension Master Gardener in Larimer County

Sometimes, what was grown and harvested in a location will provide all the necessary nutrients for your fall crop, making the job easier. For example, since peas fix nitrogen in the soil and broccoli, spinach, and lettuce need nitrogen, your fall lettuce, spinach, and broccoli crops could be planted in the spot where you grew peas in the spring.

Most vegetables that you want to harvest in the fall will need to be planted in July or early August. The three primary factors for planning and planting a fall crop are days to maturity, number of daylight hours (which decreases from late June to fall), and daytime/nighttime temperatures.

Seeds planted in July that require 60 days to mature will be ready to harvest in September. By looking at your seed packets, you can easily figure out your planting deadlines for a fall harvest. Cool season vegetables like radishes, cabbage, leafy vegetables (lettuce, spinach, arugula, endive, and kale), turnips, peas, broccoli, and beets all require between 28 and 65 days to mature, depending on vegetable and variety. A few warm season vegetables like bush beans and cucumbers will need enough time to mature before cooler weather but could be a viable fall crop if planted in early July. Because days are getting shorter, you may want to fudge days to maturity by adding an extra week of growing time, if possible.

Timing is important because warmer soils from July to September will encourage quicker growth than in early spring but plants will need enough time and light to mature by the fall when days shorten, growth slows, and the first hard, killing frost arrives. The average date for the first hard frost (temperatures <26 degrees F) is mid-October but this can vary every year and by location. By paying attention to the weather reports, you may be able to extend your harvest a little by protecting your plants on cold nights. Many cool season vegetables grown for a fall harvest are hardy enough to survive light frosts and cool daytime temperatures. In fact some, like carrots and kale, taste better or sweeter as a result of cooler temperatures. Hardy vegetables (leafy vegetables, green onions, broccoli, turnips, and radishes) can grow when daytime temperatures are as low as 40 degrees. Semi-hardy vegetables that can grow in daytime temperatures between 40 – 50 degrees include beets, short carrots, and chard. Some people also try peas as a fall crop, although yields are generally smaller than in spring. Due to temperature changes in the fall, humidity can be higher. Trellising can help insure good airflow, reducing the chance of powdery mildew of peas. Direct sowing seeds in full sun when the temperature is 90+ degrees F can be more difficult that spring sowing. You may want to sow seeds in a partially shady location and then move the young seedlings to your main growing area once the heat breaks. This approach can also help if the space vacated by your spring leafy vegetables, peas, and garlic isn’t enough to host your fall crop seeds. Or, you can sow seeds in pots on your deck and then move them to the garden as open space becomes available. To keep your fall crop seeds happy, be sure to keep them consistently moist and cool, both of which can be accomplished by using a good layer of mulch. Grass clippings make excellent mulch, if applied weekly in layers that are no more than ½” thick. Don’t use grass clippings from lawns where chemicals or weed killers have been applied, because these could affect the germination and growth of your vegetable plants. Once you’ve done all that, just sit back and wait for your fall crops to grow…and your upcoming fall harvest!