Rhubarb plants are originally from Asia but were brought to Europe and America during the 1600s. This perennial vegetable is popularly sweetened and used in tarts, jams and pies. It has tart-flavored pinkish-green stalks which are the only edible parts, since the leaves contain oxalic acid which is toxic when ingested. These plants are also prone to yellowing leaves due to certain diseases and conditions.
Rhubarb leaves turning yellow: What are the reasons?
Too much exposure to sunlight
Rhubarb plants do best in cold places, so exposing them to direct sunlight or too much heat could lead to yellowing leaves. These plants can only survive in temperatures below 40 degrees Fahrenheit. If you are growing rhubarb in a humid area, make sure to protect them from intense heat.
Place your plants in a shaded area so that they do not come into direct contact with sunlight. You can also place a screen or roll-up blinds to shade the plants from the rays of the sun.
Irregular water supply
Rhubarb leaves may also turn yellow due to an irregular water supply. The plants will wither and die if not watered regularly. Be sure to maintain a regular schedule and, during dry weather, give the plants a deep soaking at least every seven to 10 days.
Overwatering or underwatering
Your plants could be turning yellow from overwatering or if they are in poorly draining soil. To avoid this, ensure that you provide just enough water for the plants, but not too much.
Similarly, underwatering can also lead to yellowing leaves. To fix this, water the rhubarb at least every other day, especially if you are growing the plants in a warmer region. Water the plants only when the top inch of the soil is dry, and check for moisture with your fingers.
Like most plants, rhubarb needs good drainage to grow healthily. If the water stays stagnant in the soil it could lead to root rot and cause yellowing leaves. Make sure to fix the drainage system of your planters so that no excess water remains in the pots. If the plants are planted outdoors, install a garden drainage system to avoid this problem.
Another reason rhubarb leaves turn yellow is due to fungal diseases. Fungi like root and crown rot could invade the plants, causing leaves to become yellow and red, and eventually fall off. Crowns will display a brown-black decay, and large roots tend to manifest big, brown-black holes.
Ascochyta leaf spot is a fungal disease that causes yellowish-green areas on the leaves. The leaf tissues may turn brown and die, resulting in angular spots that have white centers along with red and grayish-green zones.
Anthracnose stalk rot is another fungal infection, resulting in wilted leaves and water-soaked lesions that turn black. The stems have a twisted appearance and eventually collapse.
The abovementioned fungal diseases can be remedied using good sanitation practices. Remove and dispose of infected plant tissue during the summer and after the first frost. The plants should be fertilized once growth appears in the spring, with another application once the stalk harvest is complete. Fungal diseases tend to surface when plants are stressed, so always make sure to optimize your plants’ growing conditions.
Fun facts about rhubarb
Botanical name: Rheum rhabarbarum
Sun exposure: full and part sun
Plant type: vegetable
Soil type: loamy
Soil pH: neutral, slightly alkaline
Rhubarb plants were considered vegetables since they are members of the buckwheat family, but a New York court ruling in 1847 enlisted it as an official fruit in the USA.
Rhubarb plants are tough and cold-hardy, meaning they cannot be destroyed easily unless they are burned or aggressively uprooted.
Rhubarb plants are popular as sweetened fruits added to tarts and pies. However, the leaves are toxic due to their oxalic acid. Yellowing rhubarb leaves is a common concern, and is usually due to incorrect watering. However, it could also be due to extreme heat or sunlight, or fungal diseases.
Image: istockphoto.com / ClaraNila