Rhubarb (Rheum rhabarbarum) is a perennial vegetable, often utilized as a fruit, that traditionally thrives in cool, temperate northern climates. Gardeners in the Southern United States face a significant challenge because this plant requires a prolonged period of cold to grow successfully. The deep South, with its mild winters and intense summer heat, is outside of the plant’s ideal range. This guide outlines the necessary adaptations and practices Southern gardeners must adopt to integrate this tart favorite into their landscape.
Understanding the Southern Climate Challenge
Rhubarb requires a period of cold, known as vernalization, to break dormancy and stimulate vigorous spring growth. The plant needs sustained temperatures below 40°F each winter. If this cold requirement is not met, the plant remains weak and produces thin stalks.
The primary issue is the combination of insufficient winter chill and excessive summer heat. Temperatures consistently rising above 90°F cause the rhubarb plant to enter premature dormancy or “bolt.” Bolting means the plant sends up a flower stalk, diverting energy to seed production rather than producing edible leaf stalks. Summer stress also makes the plants highly susceptible to crown rot, a fungal disease exacerbated by warm, moist soil conditions.
Selecting Rhubarb Varieties for Heat
Selecting a genetically suitable cultivar is the first step in successful Southern rhubarb cultivation. Traditional varieties often fail because they are bred for colder climates. Southern gardeners must select varieties known for greater heat tolerance and lower chill requirements.
Cultivars like ‘Macdonald’ and ‘Cherry Red’ are frequently recommended for their ability to withstand warmer temperatures better than standard Northern types. Another excellent option is ‘KangaRhu,’ which was developed to thrive in hot climates and extend the harvest window deep into the summer months. Selecting a variety that is slow to bolt, such as ‘Hardy Tarty’ (also called ‘Colorado Red’), helps maximize the limited growing season. Even with a heat-tolerant variety, the stalks may be greener rather than the deep red color seen in Northern-grown rhubarb, which is a common effect of warmer soil temperatures.
Preparing the Planting Site
Site preparation is essential for mitigating heat stress and poor drainage, the two biggest threats to rhubarb in the South. Rhubarb must be planted in a location that receives full sun in the morning but is protected from the intense, direct heat of the afternoon. Planting on the east side of a structure or under the filtered shade of a deciduous tree provides the necessary relief.
The soil must be rich in organic matter and offer excellent drainage to prevent crown rot. Before planting, incorporate generous amounts of well-rotted compost or aged manure to a depth of at least a foot, as rhubarb is a heavy feeder. If the native soil is heavy clay, planting the crowns in a raised bed is recommended to ensure water never pools around the root system. Plant the dormant crown pieces so the buds, or “eyes,” are covered with no more than one to two inches of soil, as deep planting can delay or prevent new growth.
Year-Round Maintenance and Care
Managing soil temperature is a constant effort in warm climates, and a thick layer of mulch is a primary defense against heat. Apply a three to four-inch layer of light-colored, organic mulch, such as clean straw or shredded leaves, around the plant to insulate the root zone. This keeps the soil significantly cooler and helps retain moisture needed to combat summer heat stress.
Rhubarb needs consistent, deep watering to prevent the stress that causes summer dormancy, especially during dry spells. The goal is to keep the soil moist but not waterlogged.
Southern-grown rhubarb benefits from more frequent feeding than its Northern counterparts. Apply a balanced fertilizer in early spring and side-dress with composted manure again after the brief harvest period to replenish the nutrients.
Delaying the harvest is crucial for long-term success. Refrain from harvesting any stalks in the first year after planting, and only take a small, light harvest in the second year. The harvest window typically occurs in the late winter or very early spring before the intense summer heat arrives.