Rhubarb is a perennial vegetable that produces flowers, a process known as “bolting.” Bolting is the plant’s natural reproductive stage where it shifts energy from growing edible stalks to producing seeds. While flowering is a normal part of the life cycle, gardeners try to prevent it because it affects the quality of the harvest. Bolting signals that the plant is under stress or has reached full maturity.
What a Rhubarb Flower Stalk Looks Like
The flower stalk, or bolt, is visually distinct from the regular, edible leaf stalks (petioles) that grow from the crown. It emerges as a thick, rounded stalk that grows rapidly and vertically from the center of the plant. Unlike the leaf stalks, which are slightly flattened or grooved, the flower stalk is solid, uniform, and often towers above the large leaves.
The stalk eventually develops a large, tight cluster of small flower buds at its tip. These buds open to form a plume-like structure known as a panicle, which may be creamy-white, greenish, or pink-tinged depending on the variety. This structure’s purpose is to produce seeds. If you see this tall, central growth, your rhubarb is bolting and requires immediate attention.
Why Rhubarb Starts Bolting
Bolting is triggered by several environmental and cultural factors that signal the plant needs to reproduce quickly. Plant maturity is a common reason, as older, well-established crowns (typically three to four years or more) are more likely to flower naturally. Certain heirloom varieties, like ‘Victoria’ or ‘MacDonald,’ also have a greater genetic predisposition to bolting compared to modern hybrids.
Environmental stress is another primary cause, especially factors related to temperature and moisture. Rhubarb is a cool-season plant, and prolonged periods of high heat (exceeding 75°F) or drought conditions can stress the plant into bolting. A sudden shift from extreme cold to a warm spell can also be a trigger. Poor cultural conditions, such as nutrient deficiencies, soil crowding, or not dividing older clumps, can also prompt the plant to divert energy into reproduction.
How Flowering Affects the Harvest
When a rhubarb plant bolts, it fundamentally changes its energy allocation away from vegetative growth. The plant diverts carbohydrates from the root crown and developing leaf stalks toward the production of the flower stalk and seeds. This redirection of resources is why bolting is undesirable for the gardener. Developing stalks tend to be thinner, tougher, and less flavorful because they are receiving fewer resources.
Bolting is a stress response that negatively impacts the overall eating quality. Although the stalks remain safe to eat, the reduced energy means they may develop a woody texture. The quality of the harvest is limited if the plant is allowed to continue its reproductive cycle.
Removing the Flower Stalks
If a flower stalk emerges, remove it immediately to force the plant to redirect energy back into producing edible leaf stalks and storing reserves in the root crown. The goal is to interrupt the reproductive process quickly. The flower stalk should be cut or pulled off as close to the base of the plant as possible.
Use a sharp knife or pruners to make a clean cut near the crown. Cutting the stalk at an angle can prevent water from collecting in the hollow center, which may lead to rot. Prompt removal does not ruin the plant for the season. It signals that the plant may need better care, such as more consistent watering or division, to prevent future bolting.