Basic horticulture of growing green beans

Green beans, or scientifically known as Phaseolus vulgaris L. is part of the family known as Fabaceae (Leguminosae) or legumes. Green beans can be grouped with potatoes, tomatoes, cabbage and onions in terms of their importance in human nutrition. It is not a niche crop such as cherry tomatoes so it competes as a commodity in the open market.  There are two basic types grown, the bush bean, which is harvested once off (mostly) and the runner bean grown on smaller scale and needs to be trellised and is harvested over a period of time.

Do not confuse green beans with dry beans such as sugar beans and haricot.  Green beans can be eaten raw as a vegetable while dry beans are grown for their seed which is cooked before it can be eaten.

Before considering if you should grow green beans you should ask yourself if it suits your basket of crops that you are growing and if your market will buy sufficient quantities that is economical viable. It is always a good idea to specialize, but that is a problem with open field growers. How do you apply crop rotation for maintaining healthy soil ecosystem.  So consider three large commodity crops, tomatoes, potatoes and onions that can be grown with green beans.  In general the South African market is large enough so you can sell your green beans, although competition is tough, as it is with all commodities.

Dry bean (Haricot bean) is harvested for their dry seeds and can be stored for long periods. Expect yields between 1-2 t/ha.

Green beans are grown for the fresh pods that have a short shelf life. Expect yields between 6-8 t/ha.

Green beans can be grown only where there is good irrigation water.  It is sensitive to drought stress so good quality water with low salt content is essential. Green beans are frost sensitive, so the most popular areas are Mpumalanga (Nelspruit area) and Brits area. Mpumalanga is popular since the crop can be grown throughout the year and Britz because of the high quality water and long growing season.

Climatic requirements for growing green beans

Green beans is a sensitive crop. Its stems and leaves are soft so any extreme climatic condition will affect it more than most other crops. It does not tolerate frost at all and extreme heat will cause blossom drop and curly pods.  It can tolerate temperatures up to 35°C but sufficient water during the hottest time of the day is crucial. So basically green beans can be considered a tropical crop with minimum temperatures of 10°C and max 36°C.

Day temperatures should be between 18 – 26 °C. It is the night temperatures that are really important. Expect a large amount of opaque pods if temperatures stay below 6 °C for a couple of nights. One night will not do significant damage as long as there is no frost or the temperatures goes below 0 °C.

Excessive rain and hot weather cause flower and pod drop and increase the incidence of diseases.

Wind might seem a strange limitation, but in sandy to sandy loam soils wind can cause significant damage to pod’s skin and the trellised bean stem.  Strong winds, such as in the Western Cape plays havoc with runner beans.  Not only can the poles be damaged or broken but the stems can become entangled with each other making harvesting very difficult.  Dry winds reduce pollination and yields.

In general bush beans are grown during winter only in frost free areas such as the lowveld. Just being frost free does not mean bush beans can be grown successfully. Pod development is very sensitive to low temperatures. The same can be said about the maximum day temperature.  Bush beans prefer temperatures below 28°C, but if temperatures stay above 30°C every day, one can expect significant yield losses, especially during flowering and pod formation.

Some basic facts on green/bush beans:

• Germination: +15°C
• At ±18°C germination takes ±12 days
• At ±25°C germination takes ±7 days
• Bush bean growth season length: 60-90 days depending on temperature or climate.
• Basic fertilizer requirements:
  • 20-40 kg/ha N
  • 40-60 kg/ha P and
  • 50-120 kg/ha K.
• Estimated yield: 6-8t/ha

Trellised green runner beans damaged by high winds

Although beans require irrigation water too much water, such as very high rainfall which the grower cannot control, will cause diseases such as:

• Halo blight
• Pod rotting
• Botrytis
• Anthracnose

Both halo blight and pod rotting are caused by botrytis and anthracnose.  Very wet field conditions affect harvesting especially if the beans are harvested with mechanical systems.

Soil requirements for growing green beans

Green beans growth season is very short relative to other commodity crops. Due to its sensitivity to water it does not do that well in very sandy soils. Unless you have an excellent irrigation system, it is not advised to grow it in sandy soils. Ideally one needs a soil that can retain some water during high temperatures. Obtaining optimum yields require a delicate balance between fertilizer and organic material in the soil.  Too much nitrogen will promote vegetative growth with a significant decrease in yields.

Theoretically the best results are obtained with medium sandy to loamy soils. But who has that. What is important is that on the whole, the more even the soil is over the whole production area the better a grower can apply a management system such as fertilizer and spray programs to achieve consistent quality yields.

The only soil a grower must avoid are brack soils or brack irrigation water.  Soils or water with high pH will cause magnesium deficiency and subsequent decrease in quality of yields.

Ridging is the most popular method of preparing the soil.  Some growers even grow beans on very sandy soils, but that is more to do with experience and excellent management.

Vegetable farming soil preparation. Ridges can be used for green bean production but is ideal for many types of vegetables.

Can beans be grown in windy areas?

Beans are soft plants, meaning their stems and leaves are not very “woody”.  This means that wind will either damage the leaves and stems, leaving large pockets of damaged skin for diseases to penetrate or the young seedling will be twisted and turned until the stem breaks off.

The worst situation is when beans are grown in sandy soils.  The small silica particles cuts into the flush of the pods after which bacteria and fungi can penetrate. This renders the pods unmarketable after a couple of days.

Trellised beans are worst affected. Wind plays havoc with the  uprights and quite often the whole system fails if it is not build strong enough.  The best results are obtained when runner beans are trellised inside shade houses.

Rainfall

Irrespective of the temperature, rainfall has an influence on growth. Very wet conditions promote halo blight, pod rotting which is cause by botrytis and anthracnose. The weather will also have an influence on harvesting. The pods should be harvested dry rather than wet to reduce incidence of post harvest diseases. Beans are soft succulent plants and do not tolerate drought. They quickly wilt and yields will be lowered.