Rhubarb is a hardy perennial vegetable, often utilized in cooking as a fruit, that thrives in cooler climates. Its popularity stems from its distinctive tart flavor and early spring availability. This plant is known for its robust and expansive growth habit. Understanding the potential size and growth pattern of rhubarb is necessary for successful cultivation and proper garden planning.
Typical Mature Dimensions
A fully grown, established rhubarb plant is a considerable presence in the landscape, characterized by its wide spread of foliage. The overall height of a mature clump, measured from the ground to the top of the large leaves, typically falls within the range of 2 to 4 feet. However, the horizontal spread is often the more notable dimension, with healthy plants frequently forming a large leafy clump that can span 3 to 5 feet across.
The harvestable part of the plant is the petiole, or leaf stalk, which contributes directly to the overall size. These thick, succulent stalks can reach lengths up to 18 inches and may be 1 to 2 inches in diameter at their base. Stalk length and thickness are direct measures of the plant’s vigor and the quantity of the harvest. A mature rhubarb crown requires this wide-reaching space to produce a high volume of large, thick petioles.
Influence of Cultivar and Age
The maximum size a rhubarb plant achieves is primarily determined by its genetic makeup, or cultivar, and the time it has been allowed to establish. There are dozens of varieties, and their inherent vigor dictates the final dimensions of the mature crown. Smaller, more compact varieties, such as ‘Canada Red,’ may only spread about 2 feet in diameter. Conversely, more vigorous, traditional, or heritage varieties like ‘Victoria’ or ‘MacDonald’ can easily exceed a 4-foot spread and produce longer stalks.
Rhubarb does not reach its full potential size in the initial growing season. It requires a significant establishment period to build energy reserves in its crown and root system. Growers should not harvest any stalks in the first year after planting and only a few in the second year. The plant will not reach its mature, highly productive size until the third year, after which it can remain productive for a decade or more.
The division of older clumps is also a factor in maintaining size and vigor. After five to ten years, the crown can become overcrowded, leading to smaller, less vigorous stalk production. Dividing the crown into smaller sections and replanting them helps to rejuvenate the plant. This process ensures the continued production of large, thick stalks by preventing resource competition.
Environmental Factors Shaping Growth
While genetics set the potential, rhubarb is a heavy feeder that grows best in fertile, loamy, well-drained soil rich in organic matter. Deep soil preparation, incorporating generous amounts of compost or manure, provides the extensive root system with the nutrients needed to support a large, leafy canopy.
Sunlight exposure significantly influences the growth rate and overall size. Rhubarb performs best in full sun, which maximizes the plant’s ability to photosynthesize and produce large stalks. Although it can tolerate partial shade, the size and yield will likely be reduced compared to a plant grown in an optimal location.
Consistent soil moisture is necessary for the development of large, thick petioles. Rhubarb is a thirsty plant, and growth can slow down or even stop during hot, dry periods. Regular watering, especially during dry spells, is required to help the plant achieve its potential size and prevent the stalks from becoming thin. To accommodate the typical mature spread of 3 to 5 feet, individual crowns should be spaced at least 3 feet apart at planting.