Snap beans are one of the joys of the summer vegetable garden and one of the easiest crops to grow. They thrive in garden beds and containers reliably producing a heavy crop of tender pods. That said, it’s not uncommon to see green bean leaves turning yellow. There are many potential reasons for yellowing leaves including drought, infertile soil, inadequate light, and plant diseases like blight. Below you’ll learn 7 reasons for green bean leaves turning yellow and what you can do to promote healthy growth from your bush and pole bean plants.
What are green beans?
Snap beans, also known as green beans or string beans, are a warm season vegetable and planted in late spring once the risk of frost has passed. There are two main types of beans, bush and pole. Bush beans form compact plants and pole beans vining plants that can grow 8 to 10 feet long and should be supported on a trellis or other structure. Snap beans don’t just produce green pods. There are varieties that yield yellow, purple, red, or even bi-colored pods, making it easy to grow a rainbow of beans in your vegetable garden.
Reasons for green bean leaves turning yellow
Beans are one of the easiest vegetables to grow, but it’s not uncommon to see leaves on bean plants turning yellow. It may be a natural progression of the growing season or it may indicate a problem with the soil or plants. Here are 8 potential causes of yellow leaves on bush and pole beans.
1) Lack of sunlight can cause yellow leaves
Yellowing leaves on bean plants can be the result of insufficient light. Beans grow best when planted in a site that receives 8 to 10 hours of direct light each day. They can take 4 to 6 hours of light, but won’t produce as well as they would in full sun. Yellowing leaves due to a lack of light is most common on foliage at the bottom of the plants. These leaves are older and often more shaded than the new growth at the tops of the plants. There’s not much you can do in mid-summer if bean leaves are yellowing due to shading, but I would suggest looking for a sunnier spot to grow beans in subsequent years.
2) Excess water can result in yellowing bean leaves
Too much water in a vegetable garden can be as bad – if not worse – than too little water. Excessive moisture from frequent rains or overwatering can cause root rot. The first indication of root rot is typically yellowing leaves. If you spot yellowing leaves on your bean plants consider whether the weather has been wet or if you’ve been watering too much. There’s not much you can about the weather, but if overwatering is the issue, cut back on how often you water. It’s best to base watering on need, not on a schedule. To gauge soil moisture, stick a finger into the soil at the base of the plants. If it’s dry 2 inches down, grab your hose. To help overwatered soil dry out, pull back any mulch you’ve placed around the plants.
3) Water stress can cause bean leaves to turn yellow
Bean plants have relatively shallow roots and need a steady supply of moisture to grow and crop well. A lack of water means nutrients can’t move through the soil and into your plants, triggering yellowing leaves. It’s essential to deep water in dry weather. I also apply a 2 to 3 inch layer of straw mulch between rows of bush beans and at the base of pole beans to hold soil moisture and reduce how often I need to irrigate. Adding organic matter like compost or aged manure to the bed before planting can also improve the water holding capacity of the soil. Keep in mind that soil type plays a part in how quickly it dries out. Clay-based soils hold water better than sandy soils and therefore won’t need to be watered as often.
It’s also important to know that bean plants have a higher moisture requirement when they’re flowering and setting pods. When I spot the first flowers, I pay extra attention to soil moisture and deep water when it’s dry 2 inches deep. I like to use a long-handled watering wand to direct water to the base of the plants.
4) Crowding bean plants can result in yellow leaves
Bush and pole bean plants need to be spaced at the right distance in order to access maximum light, water, and nutrients. If you overcrowd plants they’ll be in competition and that can produced stunted plants or yellowing leaves. Prevent this problem by spacing the seeds the proper distance apart or thinning seedlings once they’re growing well. Plant bush beans 2 inches apart with rows spaced 18 to 30 inches apart. Space pole bean seeds 3 inches apart at the base of a trellis.
5) Low soil fertility and nutrient deficiencies can cause bean leaves to turn yellow
When grown in soils with low fertility, bean plants can struggle with the leaves turning yellow to indicate nutrient deficiency. It’s a good idea to do a soil test every couple of years to get a greater understanding of your soil and what it may lack. To build healthy soil in my garden, I add compost or aged manure to my garden beds each spring. Beans are classified as ‘light feeders’, but adding a slow release organic vegetable fertilizer at planting time helps provide nutrients like nitrogen, phosphorous, and potassium to the plants.
Every vegetable has an ideal pH range and beans prefer a soil pH between 6.0 to 7.0. Because my native soil tends to be acidic, I lime my garden beds annually to raise the pH. If your soil pH is higher than 7.0 apply a soil acidifier to reduce alkalinity.
Many gardeners also use a legume inoculant when planting bean and pea seeds. Inoculants contain rhizobia bacterium which form a symbiotic relationship between the bean plant and the bacteria. When planting beans in soils where legumes have already grown, there are likely rhizobia strains of bacteria present in the soil. Adding inoculant is an easy way to make sure your soil contains a high population of these beneficial bacteria.
6) Plant diseases can turn bean leaves yellow
Plant diseases are one of the leading causes of green bean leaves turning yellow. There are many disease organisms including bacterial, fungal, and viral that may affect bean plants. The best way to prevent plant disease is to practice crop rotation, good garden sanitation, and space plants properly to allow for good air circulation. Here are 4 common diseases of beans:
Bacterial bean diseases
Bacterial blight, as well as halo blight, are bacterial infections that result in brown greasy looking spots on the leaves surrounded by a bright yellow halo. It’s unsightly but also affects yield because the pods develop brown lesions. In serious infestations new growth can turn yellow and die. These diseases are typically introduced through infected seed and when the weather is favorable, take hold in the garden. Ideal conditions for bacterial blights are warm temperatures and high humidity. Never save seed from affected plants and remove infected leaves and plant debris at the end of the season.
White mold in beans
White mold is a fungal disease that spreads quickly in cool, wet weather. It infects many species of crops including tomatoes and cucumbers, and affects leaves, stems, and fruits. The first signs of white mold fungus are pale colored lesions. Soon cottony fungal strands are produced and the plants turn yellow and wilt. Reduce the occurrence by practicing crop rotation, spacing plants at the proper distance, and watering early in the morning. All types of beans can be affected by white mold, but research has shown that runner beans are the most resistant.
Bean mosaic virus
There are several types of bean mosaic viruses including bean yellow mosaic virus and bean common mosaic virus. These viral infections are spread in the garden by aphids. The disease shows up as yellowing or mottling of the bean leaves. They can also pucker or become cupped in appearance. With bean common mosaic virus, an affected plant wilts and dies as the diseases progresses. With bean yellow mosaic virus the plants continue to grow and produce pods, but overall yield is affected. Plant resistant varieties, like Provider or Improved Tendergreen if this disease is common in your area. It’s also a good idea to cover plants with insect netting or row covers early in the season to prevent aphids from spreading the infection.
Bean rust is another fungal disease and is most common when the weather is warm and humid. Small reddish-brown spots surrounded by a yellow halo appear on the leaves. Serious infections can cause the leaves to turn yellow and then brown and eventually they fall off. Rust that develops late in summer won’t affect yield. Prevention starts by not overcrowding plants. Thin seedlings spaced too close together. If you spot leaves with speckling, pick them off to slow the progress of the disease.
7) Pests can cause bean leaves to yellow
Finally, insect pests like thrips or Mexican bean beetles can cause a yellowish appearance to the leaves of bean plants. Two-spotted spider mites suck sap from the undersides of leaves which results in a mottling or yellowing to the tops of the foliage. Mexican bean beetles skeletonize the leaves of bean plants which can cause them to look yellow from a distance. Close up you’ll see the lacy pattern of the damage. I inspect my bean plants often for signs of pests, damage, or webbing, in the case of spider mites. You can use a jet of water from a host to knock spider mites off plants or spray an insecticidal soap. For Mexican bean beetles, handpick adults and larvae or use an insecticidal soap.
8 ways to prevent green bean leaves turning yellow
An ounce of prevention is worth a pound of cure and now that we know more about the reasons why bean leaves turn yellow, it’s time to look at ways to prevent bean problems. Below are 8 habits to encourage healthy plant growth and a bumper crop of beans.
- Practice crop rotation – This is a smart garden habit that can reduce many potential problems. I maintain a 3 year crop rotation which means I don’t plant the same crop family in a garden bed for three years. There are many ways to approach crop rotation, but I like to group my vegetables by family.
- Using legume inoculant – Coating bean seeds with rhizobia before planting has been shown to promote plant growth and boost yield.
- Maintaining a healthy soil – Feeding soil annually with organic amendments like compost and supplementing with organic fertilizers when needed gives you a head start on plant health.
- Plant in full sun – Beans are a heat-loving vegetable and thrive when grown in beds or pots that receive 8 to 10 hours of direct sun.
- Water smart – Make it a goal to provide consistent moisture to bean plants, particularly when they start to flower and form pods. Avoid wetting the foliage when watering and try to water in the morning, not evening. Wet foliage can prompt the spread of disease.
- Clean up – If your bean plants are diseased make sure to remove plant debris and don’t compost it. You want to try and break the cycle of disease.
- Avoid working around bean plants in wet weather – As noted above, wet foliage can spread disease so stay out of the bean patch when the weather is rainy or the plants are covered in dew.
- Remove weeds – Dense weed growth can crowd out bean plants and reduce air flow. A lack of air circulation can encourage plant diseases like white mold.
For more information on other vegetable garden problems, be sure to check out these articles:
- Tomato plant diseases
- Cucumber plant problems
- 10 zucchini growing problems and how to solve them
- how to get rid of squash bugs
Have you had issues with your green bean leaves turning yellow?