Why Are My Rhubarb Leaves Turning Yellow?

Rhubarb leaves yellowing in midsummer — when the plant should be at its most lush and green — are showing a stress response. The underlying cause can range from something benign (end-of-season natural die-back) to something more serious (crown rot or waterlogging). The timing, pattern and accompanying symptoms are the clues that point to the right explanation.

Natural end-of-season die-back

From late July or August onwards, rhubarb leaves naturally begin to yellow and die back as the plant moves energy into the crown in preparation for dormancy. This is entirely normal. The stalks become less palatable and stringier at this point — this is the signal to stop harvesting for the year and let the remaining leaves die back naturally. Do not remove leaves until they are clearly dead.

Nutrient deficiency

Pale, yellowish-green leaves on young or mid-season plants that should be growing vigorously may indicate nitrogen deficiency, particularly in light or sandy soils. Apply a nitrogen-rich fertiliser or top-dress with garden compost. Interveinal yellowing (yellow between green veins) on younger leaves suggests iron or manganese deficiency from high soil pH — test and correct as needed.

Waterlogging and crown rot

Yellowing combined with wilting stems and a general collapse of the plant — particularly after wet periods — indicates the crown may be rotting. Check by exposing the top of the crown: healthy crowns are firm and white internally; rotting crowns show soft, brown, foul-smelling tissue. Crown rot caused by waterlogging requires improving drainage; crown rot from Phytophthora or bacterial causes in a permanently wet site means the plant may need to be removed and the site improved before replanting.