Why Is My Rhubarb Thin and Flowering?

Thin stalks mean a tired crown

Rhubarb is a long-lived perennial, and stalk thickness tracks the vigor of the underground crown. The Royal Horticultural Society links lots of thin stalks to a crown that is losing vigour and needs dividing, and notes crowding, old plants, and low fertility all push in that direction; more feeding and more space help. University of Wisconsin horticulture recommends dividing plants about every fourth or fifth year to keep them vigorous, which relieves the crowding that builds up as a clump ages.

Because the crown is the issue, the fix is renovation rather than anything topical. Digging and dividing an old clump into pieces with healthy buds, replanting into improved soil with room to grow, and feeding restores the vigor that produces thick stalks. This is why an old, undisturbed patch tends to decline into thin stalks and more flowering over the years.

Flowering and when not to harvest

A rhubarb plant that keeps throwing up flower stalks is spending energy on seed instead of leaves and stalks. University of Wisconsin horticulture advises removing the flower stalks when they first appear to keep the leaves growing strongly, and the RHS adds that heavy flowering often follows wet summers or over-use of high-nitrogen feed. Cutting the seed stalks out promptly each time they emerge keeps the plant's energy where you want it.

Just as important, do not keep pulling weak stalks. Wisconsin guidance is to harvest no stalks in the first year so the roots establish, and never to take more than a third of the leaves in any year; thin stalks are a cue that crown reserves are depleted and it is time to stop harvesting and let the plant rebuild. If, after dividing, feeding, removing flower stalks, and backing off harvest, the stalks stay thin, treat the cause as uncertain and ask your Extension office to help you evaluate the planting.

Sources

Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.

• University of Wisconsin Horticulture - Rhubarb, Rheum rhabarbarum — Divide rhubarb about every fourth or fifth year to keep plants vigorous; remove flower stalks when they first appear to keep leaves growing strongly; do not harvest any stalks the first year, and do not harvest more than a third of the leaves in any year.
• Royal Horticultural Society - Rhubarb — Lots of thin stalks indicate the crown is losing vigour and needs dividing, and can result from crowding, old plants, or low fertility; flowering is usually worse after wet summers or where high-nitrogen feed has been overused, and flower stalks should be removed as they appear.

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