Here I’m talking about snap beans, both bush beans and pole beans, often simply called green beans. By choosing appropriate varieties and giving thought to planting dates, you can get high yields all summer until frost.
We like Provider and Bush Blue Lake snap beans for productivity and flavor. We often sow Provider for the early and late crops, with Bush Blue Lake during the main season. Contender may have more flavor, but is less productive then Provider. Jade is a delicious, very tender bean, which grows well in hot weather, but will be a dismal failure if the soil is too cold. Our approach is to plant a succession of 6 sowings of bush beans, so we always have some at the peak of production.
Those who like flat beans often choose Romano II as a reliable producer of tasty beans whether it is hot or cool, wet or dry. Some people like yellow (wax) beans for visual diversity – the flavor is not much different from green beans. Purple-podded beans look attractive while raw, although the color fades on cooking.
We have given up on pole beans as we don’t like putting up trellises. If the advantage of standing to harvest beats the disadvantage of putting up a trellis, you’ll prefer pole beans over bush varieties. Pole beans take a few days longer to mature but can then be picked for a longer period, if they don’t get damaged by the Mexican bean beetle. Half-runner beans can be grown with or without trellises, and are capable of high yields. We haven’t grown any we really liked.
Prepare for green beans
Beans tolerate a wide pH range, and like plenty of sun and well-drained soil. They definitely don’t thrive if flooded! An open site with good air drainage will help minimize mold problems and other leaf diseases. Bush beans take 50-62 days from sowing to first harvest, a bit less once the soil is really warm. A soil temperature of 77°F (25°C) is best for germination, although a temperature of 55-60°F (13-16°C) and rising is workable for dark-seeded varieties. Air temperatures of 65-85°F (18-29°C) are best for growth.
Like all legumes, beans produce nitrogen in their root nodules, although this doesn’t peak till after the beans are being harvested. In order to grow strong bean plants, you can fertilize before the beans at about 4 oz N/100 sq ft (13.4g/sq m), and use the bean-produced fertility for the following crop. If your soil is already very fertile, you could skip fertilizing before sowing the beans. Excess nitrogen will produce lots of leaves but delay flowering. 80-85% of the nitrogen produced ends up in the bean tops, so if possible turn them under before planting the next crop, rather then remove them to the compost pile.
Because they are not planted until spring is well underway, beds for beans can grow a good stand of winter cover crops ahead of the bean crop. Winter rye should be turned under three weeks ahead of sowing, to allow the rye to break down and for the allelopathic compounds to break down. We have found wheat to be easier to incorporate and to have less of an inhibiting effect on germination of the next crop. It is usual to avoid legume cover crops ahead of legume food crops, to reduce the likelihood of spreading pests or diseases. For the same reasons, it is better to grow beans where there have not been other legumes for 3 years. Sclerotinia white mold can be avoided by rotating with sweet corn or other grass crops, and avoiding nightshades, brassicas, lettuce, or other legumes.
Start beans as early as possible
We make our first sowing 10 days before the average last spring frost date, and cover the bed with rowcover. Dark-seeded varieties are more resistant to rot in cold soils, so use these at least for the first spring sowing. To speed germination, soak the seed overnight (up to 8 hours) in tepid water. If the sowing has to be postponed after the beans are soaked, rinse them twice a day and drain. Plant in 3 or 4 days. If you wait longer than that, the rootlets will be too long and fragile.
Sow your beans
If possible, ensure the soil has enough water before you sow, as watering after sowing can cause crusting and also chilling injury to the seed from the cold water. Avoid irrigation for two weeks after sowing to reduce the chance of the seed rotting. Sow 1” (2.5cm) deep, a little shallower in spring, a little deeper in hot weather. Place seeds 2-3” (5-7cm) apart. We use the wider spacing for new seed, and the closer planting for one-year-old seed. Two-year-old beans often have a germination rate of only 50%, and are not worthwhile.
You can plant beans 2 rows to a bed, or on-the-flat in single rows with enough space to accommodate the pickers. The best spacing for optimum yield is 36 sq ins (232 sq cm) per plant. For example, 2” in-row x 18” between rows (5 x 46cm). Another advantage of close spacing is that the plants are more upright, with the beans higher in the leaves. This is less space than recommended for areas prone to fungal diseases.
Beans host nitrogen-fixing bacteria in nodules on the roots, and if you are growing beans on land that has not grown legumes before, or it’s spring and you don’t want to rely on the existing bacteria waking up, add some powdered inoculant. You could add this at each sowing, as it is cheap and easy, especially if the beans have been soaked. Simply scatter some of the black powder on the beans as if you were adding pepper to your dinner, then stir the seed gently. Each bean needs only a few specks of the inoculant to get started. Contrary to any rural myths, the inoculant does not speed germination.
Care for your beans
Don’t cultivate or harvest while the leaves are wet, since anthracnose, bacterial blight and rust disease are more likely to spread under these conditions. Hoe or machine cultivate while the bean plants are still small, and once they grow taller and bush out, few weeds will cause trouble. We have tried sowing beans through biodegradable plastic mulch, poking holes with rods and popping the seeds in. This crop stayed very clean, and withstood a drought caused by a crew member mistakenly pulling the drip tape out too soon. Sowing took a long time, and anyone tempted to try this would be advised to make a jig that punches multiple holes at once. In that way, the saved cultivation time, lack of diseases, and extended life of the plants might balance out the extra sowing time.
Irrigation is most needed during bloom, pod set and pod enlargement. Time the watering so that the leaves dry before nightfall. Beans need around 1” (2.5cm) of water until the end of May, then up to double that in summer.
Carry on sowing beans as late as sensible
To calculate your last worthwhile sowing date, subtract the number of days from sowing to harvest from your first frost date. Then count back a further two or three weeks, whatever would be a worthwhile length of harvest period for you. If you don’t have rowcover for when it turns chilly, count back another week or two in case frost is extra-early. Our first frost could be October 14, and counting back 60 days gets us to mid-August. We go with a last sowing in early August. We pay attention to weather forecasts, and when frost threatens, we cover with rowcover on the cold nights. Usually this lets us get several more pickings before any serious cold weather arrives. During the day, rowcover would stop pollination, but it does not stop beans that have already set from growing to full size.
Plant beans often for continuous harvest
Before we discovered the Pedio wasps to kill the Mexican Bean Beetles, we needed a new patch of beans coming into production every 2 weeks. We made 7 plantings at 15 day intervals. We now plan for a new patch to harvest every 20 days, sowing 6 times rather than 7. As well as saving space and sowing time, we get more beans than previously. Some of the time we pick from two overlapping patches.
To calculate the best planting dates for your farm, you’ll need four pieces of information: first possible planting date in spring, last planting date that will provide a crop in time before fall frost, first harvest date from each sowing you’ve done, and the number days you want to be picking from the same plants. For us, space is tight, and we want to pick from the same plants for 3 weeks, after which the yield goes down, and it takes too long to “search” for the ripe beans.
We determined our earliest possible and latest worthwhile harvest start dates, and then divided the period in between into a whole number of intervals. In our case we went for 20 days. If we expect the first beans to start coming in on 6/16 and the last ones on 9/24, then the period in between is 100 days long. If we want fresh beans every 20 days, we’ll need a total of 5 intervals between plantings, which is 6 sowings.
Our records tell us that for harvest dates of 6/16, 7/6, 7/26, 8/15, 9/4 and 9/24, we need to sow 4/20, 5/14, 6/4, 6/26, 7/19 and 8/7. In practice we use sowing dates of 4/16, 5/14, 6/7, 6/29, 7/19 and 8/3. Notice that beans mature faster in warmer weather, and to keep up with them, we need shorter planting intervals later in the summer. Our sowing intervals are 28, 24, 22, 20 and 15 days.
Harvest your beans
We pick beans three times a week, going for pencil-sized pods with pliable tips. In our climate, beans can size up in two days. It’s important to nip through the stem of the pod, and not leave the cap part on the plant, as this is the part which signals to the plant whether to continue cranking out beans or stop and focus on ripening seed. For the same reason, it is important to pick and discard any oversize pods.
Like many warm weather crops, beans are liable to chilling injury if over-refrigerated. If possible keep the temperature above 40°F (4.5°C), or you risk having the beans become slimy and pitted. At 40-45°F (4.5-7°C) and 95% humidity, beans can be stored for 7-10 days. Temperatures above 45°F (7°C) are likely to lead to yellowing and development of fiber.
Watch out for trouble
Scout the fields once a week, and keep a weather-eye open while harvesting or cultivating, to spot small problems before they become large ones. See the Cornell University 2016 Organic Production and IPM Guide for Snap Beans for detailed organic disease and pest control information.
By far the worst pest of beans we ever deal with is the Mexican Bean Beetle, a yellow-bronze beetle with eight black spots. Adults overwinter in plant debris, so clean up well in the fall, and try not to have your first bean planting be near the site of your last one the previous year. Here, the MBB emerge on the first cloudy day in early June. We used to flame each bean planting when numbers and damage became intolerable, and move on to the next planting. A smarter move would have been to plant a small early trap crop of beans deliberately at or near the site of the late beans the previous year, and then flame the trap crop when there are larvae, but not yet any pupae.
Nowadays we buy the parasitic wasps Pediobius foveolatus, ordering them as soon as we see the fuzzy yellow MBB larvae, which is the stage the wasps attack. The package contains mummified MBB larvae, with the wasps on the point of hatching. Set the open container under the bean plants close to some MBB eggs and larvae. Sometimes I shake out a few mummies here and there along the row. Once hatched, the wasps are very mobile, and will likely take care of your neighbors’ MBB as well. The Pediobius do not overwinter in our climate, but we have found that good control for a few years reduces numbers so that we can sometimes take a year off from buying the parasites.
See Using Pediobius Foveolatus as a Biological Control for Mexican Bean Beetles on Organic Vegetable Farms by Kim Stoner. Suppliers come and go, apart from the Phillip Alampi Beneficial Insect Rearing Laboratory, who we have been buying from for many years. Two other suppliers are Bugsforgrowers.com and Arbico, Read the instructions here.
Other insects that can damage bean crops include bean leaf beetle, potato leafhopper, seedcorn maggot, European corn borer and tarnished plant bug. Mites and slugs can also cause trouble.
The main defenses against disease are to keep the leaves as dry as possible. Consider orienting the rows to take advantage of the prevailing winds, planting on raised beds, using wide row spacing or in-row plant spacing.
Fungal diseases tend to be furry. Botrytis Grey Mold and Sclerotinia white mold are the most common.
Bacterial diseases of beans cause sunken or water-soaked brown spots perhaps with paler margins, on leaves and pods. Virus diseases cause leaves that are typically mottled, blistered or curled.
Most likely, it will be you enjoying your beans and not pests and diseases!