Rhubarb is a popular perennial known for its tart stalks, but even this robust plant can experience decline. This guide will help diagnose common problems, ranging from environmental challenges to pests and cultivation errors, to identify the underlying cause of your rhubarb’s distress.
Environmental Stressors
Rhubarb plants thrive in specific conditions, and deviations can manifest as signs of distress. Overwatering, a common issue, deprives roots of oxygen, leading to wilting leaves, a mushy, discolored crown, and root rot. Insufficient watering causes wilting and stunted growth. Assess soil moisture by feeling a few inches down to determine if the plant is too wet or too dry.
Light exposure also plays a role in rhubarb’s well-being. While rhubarb prefers full sun (at least six hours daily), too much intense sun in hot climates can lead to leaf yellowing, drying, or even burning. Too little light results in weak, spindly stalks with pale color.
Soil quality significantly impacts rhubarb health. Poor drainage, often seen in heavy clay soils, can cause waterlogging and root rot, indicated by standing water after rain or persistently soggy soil. Compacted soil similarly hinders root growth and water percolation. Rhubarb prefers slightly acidic to neutral soil (pH 6.0 to 6.8); imbalances can prevent nutrient uptake, leading to deficiencies. Temperature extremes also affect rhubarb; frost damage appears as black, shriveled leaves and soft, limp stalks, while excessive heat can cause thin stalks and overall stress.
Pests and Diseases
Biological threats can quickly compromise rhubarb health, presenting specific symptoms. The rhubarb curculio, a half-inch-long snout beetle, bores into stalks, crowns, and roots, leaving notches on stalks and leaf edges, often accompanied by sticky sap. Slugs and snails cause irregular holes in leaves, identifiable by slime trails. Crown borers can also damage the plant’s core, leading to overall decline.
Fungal and bacterial diseases are common culprits for rhubarb decline. Crown rot results in a mushy, discolored (brown or black) crown, wilting, yellowing leaves, and stunted growth, sometimes with a foul odor. Leaf spot diseases manifest as small, brown or black spots on leaves, sometimes with a yellow halo, which can merge into larger lesions and lead to yellowing and premature leaf drop.
Anthracnose stalk rot often appears after wet conditions or environmental stress, characterized by wilted leaves and large water-soaked lesions on stalks that eventually turn black, causing stalks to twist and collapse. Botrytis blight can lead to leaf, stalk, and crown rot, particularly in humid conditions with poor air circulation. Viruses, though less common, can cause symptoms like mottling or ring spots on leaves.
Improper Cultivation Practices
Improper cultivation practices can also lead to rhubarb decline. Over-harvesting, especially taking more than one-third of the stalks in a season or harvesting during the plant’s first year, can weaken the plant, reducing its vigor and future productivity. Harvesting too late in the season, particularly after hot weather sets in, or too early from young plants can also stress the rhubarb.
Incorrect planting depth for crowns can predispose rhubarb to problems. Planting the crown too deep can delay production and increase the risk of crown rot, as buds should be at or just below the soil surface. Overcrowding from a lack of division can lead to reduced productivity and smaller, thinner stalks. Weeds compete with rhubarb for essential nutrients, water, and light, hindering its growth and overall health.
Reviving and Maintaining Rhubarb Health
Addressing environmental stressors often begins with adjusting watering practices, ensuring the soil remains consistently moist but not waterlogged to prevent root rot. Improving soil drainage through the addition of organic matter like compost or by planting in raised beds can mitigate issues in heavy soils. Providing appropriate light conditions, such as partial shade in warmer climates, can prevent sun scorch, while ensuring adequate sunlight promotes robust growth.
Managing pests involves hand-picking larger insects such as rhubarb curculio, and maintaining a clean garden area to deter slugs and snails. For diseases, removing and destroying infected plant parts prevents spread, and ensuring good air circulation around plants can reduce fungal issues. Selecting disease-resistant varieties and using healthy planting stock also helps prevent future problems.
Correcting cultivation practices involves adhering to proper harvesting guidelines, such as taking only mature stalks and limiting the harvest to about one-third of the plant’s stalks. Ensure the correct planting depth for crowns, with buds just below the soil surface, promotes healthy development. Regular division of mature, overcrowded plants every few years invigorates them and maintains productivity. Consistent weeding and mulching help reduce competition for resources and maintain soil moisture.