Beans are a common feature in most gardens because they are reasonably tolerant of many conditions and quick and easy to grow.
I personally enjoy how fast pole beans climb up their trellis, eagerly watching their progress every day and waiting for those delicious pods to arrive. But while the other vegetables in the garden are being harvested, it can feel like the wait for those bean pods is never-ending, at which point you may ask yourself, “Why are my beans not producing?”.
Put simply, there are 2 broad types of beans; POLE BEANS which climb like a vine, and BUSH BEANS which have a bushier habit. Within these 2 broad types of beans is a multitude of varieties from all over the world. Both varieties can have issues with not setting fruit.
So if you’re disappointed because your beans didn’t produce fruit, didn’t set flowers, or didn’t even grow high enough, read on and you might just find the cause. It all boils down to identifying which stressor is causing the plant to focus on surviving, rather than thriving. Some common stressors are listed below:
1. Variety of beans
The timing and quantity of fruit production will depend on what type of bean you have. For example, Lima beans, otherwise known as butter beans, are warm climate beans which like long, warm days for almost 4 months. On the opposite spectrum, many bush beans and fava or broad beans are cooler climate varieties that thrive in cooler temperatures.
Tropical varieties are more sensitive to the number of daylight hours compared to varieties that thrive in temperate climates. Some Appalachian varieties from North America struggle to fruit in low humidity and people have reportedly triggered fruit production by giving the foliage a spray of water once the flowers have appeared.
In short, know your weather and microclimate and do thorough research before you order your bean seeds.
2. Heat
Like many vegetables, heat can really stress out beans. For most bean varieties, temperatures above 95 °F (35 °C) can halt both flower and fruit development. Extended hot periods can cause blossom drop, even in lima beans.
3. Cold
Some varieties, especially bush beans, won’t produce fruit until cooler weather comes along. These are also known as ‘Fall/October’ beans. When planted in spring in hot climates, they struggle to survive the summer heat and are poor producers. But when planted in mid-summer, they are ready to flower and fruit by the time the cooler weather arrives. Flava or broad beans prefer temperatures between 60 – 65 °F (15 – 18 °C), but most beans prefer temperatures between 70 – 80 °F (21 – 27 °C).
4. Daylight hours
Once the extreme heat has subsided, the next issue is the number of daylight hours. As the temperature cools, the length of the day shortens and the race is on for the plant to pollinate flowers and produce fruit before the number of daylight hours drops below 10 hours per day.
Tropical varieties tend to be more sensitive to the length of daylight hours so they flower during the equinox (when there are 12 hours of daylight per day). Unfortunately, the autumnal equinox is only a month away from the first frost for those in cold climates, so tropical varieties are unlikely to be very productive in cold climates unless you grow them in large pots and move them indoors or into a greenhouse.
Pole beans are generally less sensitive to daylight hours compared to bush beans, but bush beans tend to need a longer time to mature.
5. Lack of pollination
This is a complicated but short-lived process. Not only does the flower have to produce viable pollen, but it also has to receive the pollen during the short period that the flower is open and the stigma is receptive. In addition to this, it also requires agitation to trigger the stigma to send the pollen down to the ovaries to complete fertilization. Complicated enough, but when you look at the detail, it gets even more elaborate.
The stigma is receptive 2 days before the flower actually opens and the pollen is released the night before in anticipation of the flower opening. When the flower first opens the next morning, bees have a chance to cross-pollinate them, which also agitates the flower and triggers the fertilization process. Thanks, Mother Nature!
However, when a bee or other insect hasn’t visited the flower, it can self-pollinate when the flower closes up for the night. But it’s not over yet. In the self-fertilization situation, the flower hasn’t been agitated yet, so the pollen hasn’t been sent down the stigma to the ovaries yet. Self-pollinated flowers still need to be agitated by an insect, strong gust of wind, or blast with the hose to get the pollen moving, theoretically giving the flower a second chance to be cross-pollinated by an insect instead.
In fact, cross-pollination seems to be ‘favored’ by beans, since ‘foreign’ pollen moves faster in the race down the stigma towards the ovaries compared to the self-made pollen.
Technicalities aside, this is why flicking the flowers for the first 2 days after they open will encourage complete fertilization. Otherwise, give them a blast with the hose in the evening once the flowers have closed.
6. Wet soil
Over-watering can cause beans to drop their pods and their roots to rot. Over-watering can affect the growth of the foliage as the root system suffers from a lack of oxygen, which in turn disrupts its ability to take in nutrients from the soil. Poorly drained, wet soil also provides an ideal climate for fungus and bacteria to thrive.
You can improve your soil drainage by switching to raised beds, adding in organic matter which holds just the right amount of moisture, and mixing sand into your soil.
7. Dry soil
A small amount of wilting on the occasional hot afternoon is to be expected in hotter climates, but if a plant has wilted in the morning, this is a sign that the soil is too dry and needs a good drink. This essentially shuts the plant down. And while I have found that most beans will bounce back after a small amount of wilting once thoroughly watered, the severely wilted plants will always struggle to produce well.
Adding mulch or old compost will help to retain moisture through hot summers and slightly increase the humidity immediately around the plant.
8. Nutrient imbalance
Avoid fertilizing beans with nitrogen since, as legumes, they fix their own atmospheric nitrogen into the nodes in their root system and an excess in the soil will increase foliage growth but won’t trigger flowering or fruit production.
Instead, add small amounts of potassium during the flowering and fruiting stage to promote the production of pods and increase disease resistance. Wood ash from a fire contains practically no nitrogen, but still has approximately 5% phosphorus and 3 – 7 % potassium, making it an easy, natural fertilizer for beans and legumes in general.
9. Soil type
In general, beans aren’t very fussy when it comes to soil type as long as it is free draining. Like most vegetables, soil with a high organic matter content is always better, but be sure that it is well decomposed so that the soil doesn’t contain too much nitrogen.
10. Soil pH
While beans prefer slightly acidic soil (6 – 6.5 pH) they can tolerate a range from 5.8 – 6.8 pH. Growing them outside of this pH range will result in the plant not being able to take up certain nutrients, particularly micronutrients, and will result in discolored foliage and very few flowers.
11. Disease
Beans have the usual pests and diseases that can either limit or completely stop their production, including rust, powdery mildew, bacterial blight, and viral diseases such as bean mosaic. Appropriate watering regimes, well-drained soil, adequate airflow and aphid control can help to manage these issues to keep your plants producing.
Final tips for growing beans
When plants have finished for the year, instead of pulling the entire plant out of the ground, cut the vegetation away and leave the roots in the ground. This way, approximately two-thirds of the nitrogen that the bean fixed into its root system will be available for your next crop (rotating crops of course!)
Choosing a variety that is regionally adapted is the easiest way to ensure the greatest success rate for producing and harvesting your own beans. If you live in a cold climate and plan on experimenting with tropical beans, then germinate the seeds early indoors and be prepared to protect them from the cold.
REFERENCES
http://www.savingourseeds.org/pubs/bean_seed_production_ver_1pt7.pdf
https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_053276.pdf
https://www.ag.ndsu.edu/publications/crops/dry-bean-production-guide
https://homeguides.sfgate.com/time-plant-fava-beans-56345.html
https://www.highmowingseeds.com/blog/photoperiodism/
