Growing beans in Minnesota home gardens
The common bean (Phaseolus vulgaris), is a popular garden vegetable in Minnesota, grown for snap beans, shell beans, or dry beans. Some varieties are suited for all three uses.
Snap beans, also called "green beans" or "string beans" (although most modern varieties do not have strings), are harvested when the pods contain immature seeds, and the pods are still succulent. They are usually cooked or pickled, although they are sometimes eaten raw. "Filet" beans are snap beans that must be picked before they are thicker than 1/4 inch. They are elegant, French-style vegetables, but require very frequent harvest, as beans picked even a day too late will be fibrous and tough, and yields are lower. "Romano" beans have broad, flat pods. Pods of all types may be green, yellow ("wax"), purple, or striped. Purple pigment disappears during cooking, and cooked purple beans will appear dark green.
Shelling beans, sometimes called "horticultural beans," are harvested when the pods have begun to dry and become more fibrous, and the seeds are fully sized but still soft. The seeds are removed from the pods ("shelled out"), and are used as a vegetable side dish or in soups.
Dry beans are harvested when the pods and seeds have completely dried. Dry beans keep indefinitely and have many uses. They are particularly valued as a high-protein, high-fiber food. Although dry beans are inexpensive and widely available in grocery stores, gardeners often find that their homegrown crops are cleaner and cook faster. The selection of dry beans available through seed catalogs is much greater than the selection of dry beans in grocery stores, with hundreds of different sizes, colors, markings, and uses. Because most beans are non-hybrids and all are self-fertile, you can also save dried seed for future planting (see Saving Vegetable Seeds).
Food safety notes
Home-canned beans are one of the most common sources of botulism poisoning. (Properly prepared pickled beans, because they contain so much acid from vinegar, do not cause this poisoning.) If you wish to put up jars of beans, you must follow canning instructions exactly, including the use of a pressure-canner to process the jars (see canning green or yellow beans). If you do not have a pressure canner, plan to freeze the beans (see freezing vegetables).
Of all common beans, only kidney beans are considered toxic when raw. Both red kidney beans and white kidney beans (sometimes called "cannellini") contain toxins that are denatured during cooking. It's unlikely that anyone would actually try to eat a truly raw dried bean, but some people try sprouting their seeds, while others may be impatient with a pot of chili that's taking a long time to cook. Kidney beans are not suitable for sprouting, and they must be cooked thoroughly.
Bean growth habits include pole beans, bush beans, and half-runners. Pole beans are twining vines growing up to six feet and sometimes taller that must be supported. Bush beans are upright plants that do not need support, growing about two feet tall. Half-runner vines can benefit from some support, although they usually don't grow to more than three feet tall. Pole beans flower continuously, producing new pods all through the season. Bush beans have a more concentrated period of flowering and pod set, although they may continue to flower and produce pods as long as they are regularly harvested.
The concentrated production of bush beans makes them suited to canning and freezing, since a large harvest of beans can be gathered at once from a row of plants. Pole beans can be harvested many times during the summer, with enough beans gathered for that day’s meal. Pole beans are well suited to smaller gardens, taking up less ground than would be necessary to get similar production from bush beans. Another advantage in growing pole beans is that when the weather is extremely hot during flowering, bean plants may not set fruit. For bush beans, because all the flowers are produced during a short span of time, a large portion of the crop can be lost. Pole beans will fail to set only a few pods, and then continue producing more once the weather returns to normal.
Beans are in the legume family, Fabaceae, as are peas, alfalfa, and clover. Like these species, they "fix" atmospheric nitrogen in nodules on their roots, through a relationship with the soil-dwelling bacterium, Rhizobium. These bacteria, living in growths on the roots, can extract the nitrogen from the air and make it available to the plant, improving plant growth and yield. Many soils in Minnesota have adequate populations of Rhizobium to form the beneficial relationship with beans. However, to be sure, you can purchase powdered Rhizobium inoculum and treat the seeds before planting, by adding a little of the powder to the seed packet and shaking. Be sure to purchase inoculum suitable for beans, and not specifically for peas.
Beans should be planted once the soil has warmed. In much of Minnesota, this is not until late May or even early June. Bean seed planted in cold soil may rot rather than germinate, and plant growth will be very slow in cooler weather. Some gardeners plant bush beans in succession, every two weeks until early August, for continuous production throughout the summer and into fall. Pole beans will continue to flower and bear until frost, so there is no need for succession planting.
Plant seeds about an inch deep, or according to package directions. Very small-seeded beans should be planted more shallowly than larger seeds.
Pole bean supports should be put in place at planting time. Make a simple trellis of six-foot stakes and twine, or set up a teepee of bamboo poles or long branches. Plant seeds in a row in front of the trellis. Seeds should be planted four inches apart or two to four seeds at the base of each pole.
Bush bean seed should be sown in single or double rows, with seeds four inches apart and rows two to three feet apart.
Soil pH and fertility
Beans grow best in slightly acidic to neutral soil, pH between 6 and 7. Clay or silt loams are better suited to bean production than sandy soils, although good drainage is important. Have your soil tested (see Understanding Your Soil Test Report) to determine your soil's pH and whether it should be amended. Incorporate well-rotted manure or compost at planting to increase soil organic matter (see Composting and Mulching).
Continuous use of high phosphorus fertilizer such as 10-10-10 or 15-30-15, or high rates of manure or manure compost results in phosphorus buildup in the soil. Although phosphate fertilizer applied to soil is bound tightly and resistant to movement in the soil, some runoff may occur. It can then become a major pollution concern in our lakes, rivers and streams. High levels of phosphorus support over-production of algae, which causes significant reduction in water quality (see Preventing Pollution Problems from Lawn and Garden Fertilizers). If your soil tests high in phosphorus, use a low phosphorus (such as 32-3-10, 27-3-3, or 25-3-12) or no phosphorus (such as 30-0-10 or 24-0-15) fertilizer.
Proper watering will enhance good production. Soak the soil thoroughly when watering, to a depth of at least one inch each week during the growing season. Beans grown in more moisture-retentive soils may not need watering except during particularly dry spells, but those grown in sandy soils almost certainly will require frequent watering. Mulching three to four inches deep with herbicide-free grass clippings, weed-free straw, or other organic material will help retain soil moisture and help suppress weeds, decreasing the need for frequent cultivation.
Frequent, shallow cultivation will kill weeds before they become a problem. Bean plants form a deep taproot, but also have some lateral roots closer to the surface of the soil, so it's important not to cultivate too deeply. Be careful not to damage the plants when cultivating. A dense stand of bush beans will discourage weeds within the row.
Snap beans can be picked at any stage of pod formation until the shape of the individual seeds inside becomes apparent, causing the pods to bulge. After this stage, the pods are typically less juicy and more fibrous. Beans for canning are sometimes picked at this more mature stage, so that they remain firm after processing. Filet beans must be picked when very slender, but for other types, yield is lost by picking before the pods have gained more size. Snap beans will hold their quality after picking for several hours at room temperature, but it's best to refrigerate them if they are not to be cooked immediately.
Shelling beans should be harvested when the pods have become thin and tough, but not yet dry. The beans within will have developed their mature markings, although their color may still be pale. The pods should split open fairly easily, and the beans will be easily removed. Cook immediately or refrigerate.
Some gardeners can shelled beans; as with snap beans, a pressure-canner must be used. Alternatively, freeze the shelled beans.
Dry beans are harvested when the pods are dry and the beans inside are dry enough to rattle. If the cold, rainy weather of autumn comes before the beans are fully mature, the entire plant should be cut or pulled and hung upside down to dry indoors. Once the pods and beans are completely dry, strip the pods from the plants and shell out by hand. For a larger crop, place the pods in a burlap sack and thresh by hitting the bag with a stick. Alternatively, a child could be encouraged to dance on the sack.
The seeds are likely to be mixed with some chaff once separated from the pods and plants. Winnowing is the process of removing little bits of plant material from the seed: take the seeds outdoors on a dry, windy day and pour them from container to container, allowing the wind to blow through the stream of seeds. Lightweight plant fiber will be blown away. Store the seed in bags, jars, or other containers in a dark, dry place.
For assistance in diagnosing unknown problems visit the diagnostic site What's wrong with my plant?
Cutworms chew stems at the soil line, leaving the severed tops uneaten. Bean leaf beetles feed on leaves, especially young tender ones. Feeding on seedlings is especially damaging and can kill plants.
A number of root-rotting pathogens can infect beans. The plants begin to brown and die from the soil up, and eventually collapse. It's very important to rotate beans around the garden, not planting in the same spot more than one year in four. Peas are hosts to the same diseases, so make sure to account for all legumes in planning the rotation.
Viruses can be a problem in bean production. Viruses typically are spread from one plant to another by insects, so if you notice single plant in a row that has usual leaf coloration or strangely puckered leaves, you should pull the entire plant and dispose of it. Many bean varieties are resistant to viruses, and selecting resistant types is the easiest way to prevent disease.
Beans are susceptible to a wide variety of leaf spot diseases that result in a variety of colored spots on bean leaves and pods. Anthracnose, rust, several bacterial leaf spot diseases, powdery mildew and downy mildew are all possible. Poor air circulation creates conditions favorable for these diseases. Avoid overly dense rows, control weeds, and provide support for climbing beans to improve air circulation around plants. Resistant varieties are available for many of the leaf spot diseases.
Other kinds of beans
There are a number of other bean species that can be grown in Minnesota gardens.
Scarlet runner beans (Phaseolus coccineus) produce long vines, up to ten feet, and require a trellis. Their abundant red, pink, or bicolor blooms are attractive to hummingbirds, and this plant is often used as an ornamental. Pods have a rich, delicious flavor, and should be picked when fairly short, between four and six inches, and used as snap beans. Once the pods become too tough for snap bean use, the immature seed can be shelled out, or allowed to mature and dry. Dried runner bean seed can be cooked like dried common bean seed.
Soybeans (Glycine max) can be grown very successfully in most of Minnesota. "Vegetable soybeans" or "edamame" are varieties selected for use as fresh shelled beans. Culture is similar to that of common bean culture. Plants are tall, up to three feet, but sturdy and upright, requiring no support. Inoculation with Rhizobium may improve plant performance and yield. Rabbits and woodchucks eat soybean plants, so fencing to keep out these animals may be needed.
Pods should be picked when plump seeds have caused them to bulge, but while still green. The hairy pods are not eaten, but typically the beans are cooked in boiling water while still in the pod, then shelled out after cooking. Home gardeners can grow black-seeded varieties, in addition to the green edamame that are available frozen in grocery stores.
Do not eat raw soybeans.
Lima beans (Phaseolus lunatus) are an old-fashioned garden treat, shelled out or allowed to mature and dry. However, they require warm soils, warm weather, and a somewhat longer growing season than common beans. Some areas in Minnesota with hotter, longer summers are better suited to lima production than others. During a cooler-than-normal summer, they will perform poorly. Many Minnesota gardeners have turned to vegetable soybeans or shelled common beans as a substitute for fresh limas, since they perform better in most parts of the state, but for gardeners who love that buttery lima taste, there are a few lima bean varieties requiring less heat and a shorter season. It's worth consulting seed catalogs or seeking out a garden center with a wide seed selection to find the most appropriate varieties for your garden.
Choose either pole or bush plant habits and grow limas just as you would common beans. While the ideal soil for common beans is a well-drained clay loam, lima bean plants perform best in a coarser-textured, sandier soil. Harvest for fresh shell beans when the seed color has changed from green to cream or white, and the pods are starting to bulge in the shape of the seed. For dried limas, allow the pods to dry completely, and then thresh as you would common beans.
Raw lima beans may contain small amounts of toxic glucosides. Although most modern varieties contain little or none of the toxins, cooking lima beans is the way to deactivate any that are present. Consumption of raw limas cannot be recommended.
Yard long beans (Vigna unguiculata) are also known as "asparagus beans," and are popular in Asian dishes. They can be grown in Minnesota, although yields are likely to be low, as this species requires vary warm weather to produce pods, and the pods can suffer chilling injury from temperatures in the forties. The very long vine of this plant-sometimes more than ten feet-requires support. Some varieties produce pods up to 18 inches, others more than two feet. Watch the developing pods, which may appear puffy or inflated while elongating. They will appear tight or constricted when they are over-mature, so pick when they are long, tender, and slightly puffy-looking, before seeds expand.
Blackeye peas and cowpeas (Vigna unguiculata) are the same species as yard-long beans, and have similar requirements for warm soils and warm air temperatures. These varieties are grown for the mature dried seed, and usually are bush-types, rather than tall vines. In cooler parts of the state, the growing season may not be long enough or warm enough to fully mature the seed. One short-season variety to try is 'California Blackeye 46.'
Fava beans (Vicia faba), unlike other beans, require conditions similar to those needed to grow peas: cool temperatures with highs only into the low eighties. In most of Minnesota, favas will set only a few pods before the weather turns too hot. In cooler areas, such as along the Lake Superior shore, fava production may be successful.
Grow as you would peas, planting early in the spring. The sturdy, erect plants do not need support. The pods will first be held upright, then begin to droop as the seed matures. Picked green, as the seed starts to bulge a bit in the pod, favas should be shelled from the pod, then the whitish outer coating of the seed removed either before or after cooking. Fully mature favas are also used as dry beans.
Some people are sensitive to raw favas and can become quite ill if they eat them. Although the sensitivity to the raw seed is most common among people of Mediterranean ancestry, it's impossible to predict who will be affected. Favas should always be well cooked before consumption.
Hyancinth bean (Lablab purpureaus, Dolichos lablab) with its beautiful purple flowers, is most commonly grown as an ornamental vine in Minnesota, but the green pods can be eaten, as they are in India. Harvest as for snap beans, when the pods are juicy and tender. They should always be cooked, since the seed can contain toxins that are deactivated in cooking.