Planting green beans (Phaseolus vulgaris) in August is a common practice known as succession planting, aiming for a fall harvest. This fast-growing, warm-season annual is suitable for a second planting after the primary spring crop finishes producing. Successfully growing beans in late summer depends on careful timing and adaptation to unique challenges, such as residual heat and impending cold weather. The feasibility of this late-season planting requires a precise calculation based on the local climate and the specific bean variety chosen.
Calculating the Window for a Successful Crop
The success of an August planting hinges on determining the number of days between sowing the seed and the region’s average first frost date. Green beans are highly sensitive to cold, and even a light frost can cause significant damage to the plant’s tender tissues, halting growth and ending the harvest. To calculate the latest viable planting date, a gardener must first identify the average first frost date for their specific geographic location.
From this frost date, it is necessary to count backward the variety’s “Days to Maturity” (DTM) listed on the seed packet. This number provides the minimum growing period required until the plant begins to produce harvestable pods. An additional buffer of 10 to 14 days must be added to the DTM to account for the “fall factor.”
The fall factor is a practical adjustment because plant growth naturally slows as the days shorten and temperatures cool in late summer and early fall. Reduced daylight hours and lower temperatures decrease the rate of photosynthesis, meaning the bean plant will take longer to reach maturity than it did during the peak light and heat of mid-summer. For example, a variety with a 50-day DTM might actually require 60 to 64 days to yield a harvest when planted in August.
Choosing Rapid-Maturing Varieties
Selecting the right variety is a major factor in ensuring a successful fall crop before the cold weather arrives. The most successful August plantings utilize varieties with a short Days to Maturity, generally under 60 days from seeding to first harvest. Bush bean varieties are overwhelmingly preferred for late-season planting because they mature quickly and produce their harvest in a concentrated period.
Bush beans typically require only 50 to 60 days to mature, making them ideal for the compressed time frame of a fall crop. Popular rapid-maturing bush varieties include ‘Provider’ and ‘Contender,’ which can often be ready for harvest in approximately 50 days. These varieties produce a compact plant that does not require trellising, simplifying the setup for a late-season garden bed.
Pole bean varieties, while capable of producing a heavier, longer harvest, are less suitable for August planting because they take longer to develop a mature plant structure and begin flowering. Although some pole beans can mature in as little as 55 to 60 days, the risk of an early frost cutting the harvest short is higher compared to the faster bush types. The goal for a fall planting is a quick, concentrated yield, a trait best supplied by bush beans.
Specific Planting Techniques for Late Summer
Planting green beans in August means dealing with soil temperatures that are significantly warmer than those in the spring, requiring specific adjustments for successful germination. Green bean seeds germinate best when the soil temperature is between 70 and 85 degrees Fahrenheit. Since August soil temperatures often exceed this range, steps must be taken to prevent the seeds from drying out or failing to germinate due to heat stress.
The soil bed should be prepared by incorporating organic material, such as compost, which helps to increase the soil’s capacity to retain moisture. Seeds should be planted slightly deeper than the standard spring recommendation, typically around one to two inches deep, to reach cooler and more consistently moist soil. Firming the soil surface after planting ensures good seed-to-soil contact, which is necessary for proper water absorption and germination.
The most important technique for late-summer planting is consistent and deep watering immediately after sowing and throughout the establishment period. Watering should be thorough, aiming to moisten the root zone deeply rather than just sprinkling the surface, to encourage strong root development and mitigate the effects of high air temperatures.
Protecting the Harvest from Early Cold
As the fall season progresses, the focus shifts from managing heat to protecting the crop from sudden drops in temperature, especially when the first frost is predicted. Green bean plants thrive when daytime temperatures are between 70 and 85 degrees Fahrenheit, and their growth can be stunted if nighttime lows consistently fall below 50 degrees Fahrenheit. A temperature of 32 degrees Fahrenheit or lower will likely cause irreversible damage to the entire plant.
Monitoring local weather forecasts becomes important to anticipate the first light frost, which is the signal to deploy protective measures. Several methods can be used to protect the harvest:
- Simple physical barriers, such as lightweight row covers or blankets, can be draped over the plants to trap heat radiating from the soil and create a warmer microclimate.
- These covers should be removed during the day to allow for sunlight and air circulation.
- Another useful method involves applying a thick layer of organic mulch around the base of the plants.
- Harvesting all mature or nearly mature pods before the forecasted frost is also advisable, as beans will not survive the cold and may continue to ripen slightly after being picked.