Rhubarb (Rheum rhabarbarum) is a perennial vegetable cultivated for its thick, edible leaf stalks, which possess a distinctly tart flavor. It is a long-lived plant that requires a chilling period to break dormancy and stimulate spring growth. Successful, long-term cultivation relies heavily on selecting the correct location to ensure high yields of tender stems. Understanding the plant’s needs before installation is paramount because, once established, rhubarb can remain productive in the same spot for over a decade.
The Optimal Light Environment
Rhubarb requires a location that receives full sun exposure to maximize the energy available for stalk production. Full sun is defined as a minimum of six hours of direct, unfiltered sunlight each day throughout the growing season. This high light intensity promotes vigorous growth and the development of large leaves necessary to support the root system. In cooler climates, such as USDA hardiness zones 3 through 6, an open, all-day sun spot is the most beneficial choice.
However, the light requirement changes significantly in warmer regions, particularly those classified as zone 7 or higher. Rhubarb is a cool-season crop that thrives when summer temperatures remain below an average of 75°F. When temperatures consistently exceed this threshold, the plant experiences heat stress, which can trigger dormancy or cause it to prematurely send up a flower stalk, a process known as bolting.
To mitigate heat stress in warmer areas, providing partial shade is necessary for continued plant health. Partial shade means the plant receives gentler morning sun followed by protection from intense afternoon rays. Locating the plant on the east side of a structure or tree canopy allows for this specific light pattern and helps keep the environment cooler. This strategic placement prevents the plant from shutting down during the hottest part of the summer, ensuring the production of tender petioles.
Essential Soil and Water Requirements
Beyond light, the quality of the soil and the availability of water are paramount. Rhubarb requires a deep, rich, and well-drained soil structure to support its root system. Loamy soil is ideal because it retains moisture while allowing excess water to drain away. Amending the planting site with significant amounts of organic matter, such as well-aged compost or manure, is recommended before planting.
This high organic content improves drainage in heavier clay soils and increases water-holding capacity in lighter, sandy soils. Rhubarb is susceptible to crown rot if its roots sit in standing water, making excellent drainage essential for site selection. While the plant can tolerate a wide pH range, a slightly acidic to neutral soil, between 6.0 and 6.8, supports optimal nutrient uptake.
Rhubarb needs consistent moisture to produce large, succulent stalks. The soil should be kept uniformly moist, especially during dry spells and the active growth phase in spring and early summer. Watering must be deep enough to penetrate the entire root zone, ideally to a depth of about 12 inches. Inadequate water will cause the large leaves to wilt and reduce productivity.
Planting Techniques and Initial Maintenance
Rhubarb crowns should be planted in early spring, as soon as the soil becomes workable, or during the fall after the plants have entered dormancy. Mature rhubarb plants can spread up to four feet wide, requiring sufficient space. Crowns should be spaced at least three to four feet apart to ensure good air circulation and prevent competition for resources.
The planting depth directly affects the plant’s establishment and future production. The crown, where the buds are located, should be planted so the buds are covered with no more than one to two inches of soil. Planting too deeply can delay the plant’s emergence and hinder its vigor. After positioning the crown and firming the soil gently, the area should be thoroughly watered to settle the roots.
Applying a 3- to 4-inch layer of organic mulch, such as clean straw or compost, around the plant is recommended. Mulching helps suppress weeds, retain consistent soil moisture, and regulate soil temperature. The entire first year after planting must be dedicated to allowing the root system to establish itself, meaning all harvesting should be avoided. A light harvest can be taken in the second year, but the plant should only be harvested freely from the third year onward.