Seeing those bright green leaves on your rhubarb plants slowly turn yellow can be worrisome for any gardener. Rhubarb leaves turning yellow is usually a sign that something is wrong and the plant is under stress. The good news is that with the right troubleshooting, you can get your rhubarb back to health.
In this article, we’ll look at the five most common reasons behind yellow rhubarb leaves and what you can do to fix the problem. With a little TLC, you can have your rhubarb looking lush again.
Understanding Rhubarb Plants
Before diving into the reasons for yellow leaves, let’s do a quick rhubarb refresher
Rhubarb is a cool weather perennial vegetable typically grown for its edible stalks. It has large, triangular green leaves that are vital to the plant’s growth through photosynthesis.
While the tart, red stalks are edible, the leaves contain high levels of oxalic acid and are toxic. So be sure to remove and discard any leaves.
Rhubarb thrives in cool climates and moist, well-draining soil rich in organic matter. It can tolerate partial shade but does best with 6-8 hours of sunlight. Established plants require heavy watering.
Common pests include slugs, snails, and aphids. Diseases to watch for are crown rot, root rot, and powdery mildew.
Now let’s look at what causes the leaves to turn yellow.
5 Common Causes of Yellow Rhubarb Leaves
There are five main culprits that can result in yellow rhubarb leaves.
1. Nutrient Deficiencies
Lack of key nutrients is a very common cause of yellowing. Rhubarb needs a regular balance of nitrogen, phosphorus, potassium, and trace minerals.
Nitrogen is particularly important. Without enough nitrogen the leaves turn yellow or red as chlorophyll production slows.
Iron is also essential for chlorophyll and photosynthesis. Yellowing between leaf veins often signals iron deficiency.
Other deficient nutrients like magnesium and sulfur can also yellow the leaves. Fertilizing with a balanced soluble plant food prevents many deficiency issues.
2. Overwatering
While rhubarb needs moist soil, overwatering is a prime cause of yellow leaves. Too much water suffocates the roots, encouraging fungal diseases like root rot.
Wilted yellow leaves at the base indicate overwatering. Let the soil dry out between waterings and ensure good drainage.
3. Underwatering
The flip side of overwatering is not watering enough. Underwatering causes the leaves to dry out, wilt and turn yellow. Consistent deep watering is vital, especially in midsummer heat.
4. Extreme Temperatures
Rhubarb prefers consistent cool temperatures between 45-75 F. In hot climates, leaves may yellow due to heat stress. Move pots to a shadier spot or provide a shade cloth.
At the other extreme, a late cold snap can damage leaves. Shelter rhubarb in a cold frame or tunnel if frost threatens after spring growth starts.
5. Pests and Diseases
Various pests and diseases can turn rhubarb leaves yellow.
Aphids are a common culprit. Their feeding damages leaves, allowing fungus to enter.
Powdery mildew coats leaves in white fungal spores, eventually yellowing and killing them.
Crown rot is a serious fungal disease that yellows the leaves as it kills the plant crown.
Prompt identification and treatment of any infestation is key to saving your rhubarb.
How to Fix and Prevent Yellow Rhubarb Leaves
Once you’ve identified the cause of yellowing, here are some tips to get your rhubarb back in top form:
- Test and amend soil to ensure proper pH and nutrient levels
- Fertilize in early spring and midsummer with a balanced plant food
- Water thoroughly when top 2 inches of soil are dry
- Mulch to conserve soil moisture and reduce weeds
- Prune out dead or damaged leaves to encourage new growth
- Treat pests with insecticidal soap or neem oil
- Treat diseases with fungicides labeled for edible crops
- Improve airflow and sunlight with proper spacing and rotation
Prevention is the best medicine when it comes to yellow leaves. Proper planting techniques, soil nutrition, and pest management will keep your rhubarb thriving for years to come.
Common Rhubarb Leaf Problems and Solutions
To recap, here are some common rhubarb leaf issues and how to fix them:
Problem: Leaves yellowing from the edges inward
Cause: Nitrogen deficiency
Solution: Fertilize with a nitrogen-rich plant food
Problem: Yellow spots or blotches on leaves
Cause: Leaf spot fungus
Solution: Remove infected leaves. Spray with fungicide. Improve airflow.
Problem: Leaves wilting and turning yellow
Cause: Overwatering
Solution: Allow soil to dry between waterings. Improve drainage.
Problem: Leaves yellow and dried out
Cause: Underwatering
Solution: Water more frequently. Mulch to retain moisture.
Problem: Curled yellow leaves
Cause: Aphid infestation
Solution: Spray insecticidal soap. Attract beneficial insects.
Caring for Rhubarb Through the Seasons
Rhubarb needs slightly different care through the seasons to keep leaves green and healthy:
Spring
- Fertilize as soon as buds break dormancy
- Remove any winter mulch or protection
- Weed and cultivate lightly around crowns
- Water regularly as growth resumes
Summer
- Water deeply during drought, mulch to retain moisture
- Watch for infestations and disease
- Remove flower stalks to encourage leaf growth
- Harvest no more than 50% of stalks
Fall
- Allow last harvest 2-4 weeks before first frost
- Leave at least 50% of stalks for winter reserves
- Cut down dead foliage after frost blackens it
- Mulch crowns 4-6 inches deep for winter
Winter
- Check mulch after hard frosts and refresh if needed
- Remove mulch in early spring to allow soil warming
- Avoid fertilizing late in fall to prevent winter growth
Adjusting care by season will keep your rhubarb healthy and productive for decades to come.
Frequently Asked Questions about Yellow Rhubarb Leaves
Here are answers to some common questions about yellow rhubarb leaves:
How do I know if I’m overwatering my rhubarb?
Signs of overwatering include yellow lower leaves, soft or brown leaves, and fungus on leaves or stalks. Rhubarb should be watered when the top 2-3 inches of soil are dry.
Should I remove yellow rhubarb leaves?
Yes, pruning off damaged yellow leaves encourages new healthy growth. Just be sure to discard the leaves safely since they are poisonous.
What nutrient deficiency causes yellow rhubarb leaves?
Lack of nitrogen is the most common deficiency leading to yellow leaves. Iron, sulfur and magnesium deficiencies can also cause yellowing.
Can leaf spot or crown rot be treated?
Leaf spot can be managed with fungicides. Remove and destroy infected leaves. However crown rot is often fatal if the crown is badly infected.
How do I protect rhubarb from late spring frosts?
Cover rhubarb with cloches, cold frames or fabric row covers to protect emerging leaves from frost damage and yellowing.
Give Your Rhubarb Some TLC
With the right troubleshooting and care, yellow leaves won’t slow down your rhubarb for long. A little TLC to correct nutrient levels, moisture, and pest problems will soon have it flourishing again. Just be sure to remove any toxic yellowed leaves so you can safely enjoy those tasty tart stalks.
Creating a Stress-Free Zone
Adjust your Giant Rhubarbs environment to prevent yellowing. Ensure its not in direct, harsh sunlight which can stress the plant. Move it to a spot with bright, indirect light. Monitor soil drainage and pH, and adjust as necessary to maintain a happy, stress-free plant.
Unwanted Guests: Pests
Aphids and spider mites are the party crashers of the plant world. Theyll suck the life out of your Giant Rhubarb, leaving yellowing leaves in their wake. Regular inspections and prompt pest control are your best defense.
Crown rot and leaf spot are the villains here. Look for spindly stems and lesions that seem to have a life of their own. These symptoms are your cue to start disease management, stat.
For leaf spot, remove affected areas and keep the ground debris-free to prevent spores from overwintering. With crown rot, its often best to remove and destroy the plant to prevent further spread.
Temperature, sunlight, and drainage arent just weather talk; theyre critical to your Giant Rhubarbs mood. Too hot, too cold, too wet, too dry – any extreme can turn leaves yellow.
Sunlight is like the plants daily coffee. Too little, and its lethargic and yellow. Too much, and its burnt out. Aim for the Goldilocks zone of light exposure.
Drainage is key. Poor drainage invites diseases like crown rot. Ensure your soil is well-draining to keep your Giant Rhubarbs feet dry and healthy.