Rhubarb is a hardy perennial known for its tart stalks, which can remain productive for decades. Successful, long-term harvesting requires careful site selection. Understanding the plant’s sun exposure needs is primary, as ideal conditions shift depending on the climate. The proper balance of light and temperature determines whether the plant thrives or struggles.
Optimal Sunlight Requirements
Rhubarb generally prefers full sun (six or more hours of direct sunlight daily), especially in cooler, northern climates where heat is not a concern. This high light exposure supports the robust photosynthesis required to produce large, thick, edible stalks. Sufficient energy is needed to fuel vigorous spring growth and establish a strong crown.
The full sun recommendation must be adjusted based on geographic location and summer heat intensity. In warmer regions, such as USDA zones 7 and 8, or where temperatures exceed 75°F, full, all-day sun is detrimental. Here, the plant performs best in partial sun or dappled shade, receiving four to six hours of direct morning sun followed by afternoon protection.
The goal is to provide bright light for energy production while avoiding heat stress. Planting rhubarb on the east side of a structure or tree allows it to capture gentler morning rays. This shields it from the harshest late afternoon sun, ensuring a productive patch rather than one that quickly goes dormant.
Managing Heat and Sun Stress
Exposure to intense, direct afternoon sun can severely damage the rhubarb plant. The large, tender leaves are susceptible to sunscald, which appears as faded or bleached patches. This damage reduces the leaf’s ability to photosynthesize, weakening the entire plant structure.
Excessive heat causes premature dormancy. Rhubarb is a cool-season perennial requiring cold dormancy to regenerate successfully. When temperatures consistently exceed 75°F, the plant enters survival mode, slowing or stopping stalk production to conserve energy. This greatly reduces the harvestable yield.
High heat can also trigger bolting, where the plant sends up a tall flower stalk. Bolting is an energy-intensive process that diverts resources away from the edible leaf stalks, resulting in thinner petioles. Gardeners should promptly remove any developing flower stalks to redirect the plant’s energy back toward productive vegetative growth.
Preparing the Planting Site
The perennial nature of rhubarb demands meticulous site preparation for long-term health. Rhubarb is a “heavy feeder,” requiring soil exceptionally rich in nutrients and organic matter to support its large leaves and stalks. Incorporating a generous amount of well-aged compost or manure into the planting area before setting the crown is beneficial.
Excellent drainage is necessary for preventing crown rot. The root system of rhubarb cannot tolerate wet conditions, so avoid planting in dense clay or low-lying areas. If the native soil is heavy, amending it with organic material or planting on a slight mound improves water percolation.
Rhubarb plants grow quite large, often reaching up to four feet in width and height. Ample room is necessary for them to spread out.
Spacing and Air Circulation
A spacing of at least three to four feet between plants is required. This ensures good air circulation and prevents competition for nutrients.
Soil pH
The soil should ideally have a slightly acidic pH, ranging from 6.0 to 6.8. The plant is adaptable, however, as long as fertility and drainage are optimal.