By Richard Jauron, Greg Wallace
Rhubarb is a popular part of many Iowa gardens. Iowa State University Extension and Outreach horticulturists discuss rhubarb flowering and stalk condition and offer harvesting tips. To have additional questions answered, contact the ISU Hortline at 515-294-3108 or hortline@iastate.edu.
Why is my rhubarb flowering?
Flower development is natural for rhubarb and most other plants. Drought, extreme heat and infertile soils may encourage flowering. Age is another factor. Older plants tend to flower more than younger ones.
Regardless of the reason, flower stalks should be promptly pulled and discarded. Plants will be less productive if allowed to flower and set seeds.
Flower formation can be discouraged with good cultural practices. Water rhubarb plants every seven to 10 days during dry weather. Sprinkle ½ cup of an all-purpose garden fertilizer, such as 10-10-10, around each plant in early spring. Control weeds by shallow hoeing, hand pulling or mulching.
Why are my rhubarb stalks small and spindly?
Newly planted rhubarb will initially produce small, spindly stalks during its two-year establishment period. The stalks of large, old plants may be small and spindly because of overcrowding. Poor plant vigor due to poor cultural practices is another possibility.
After planting rhubarb, wait two years (growing seasons) before harvesting any stalks. The two-year establishment period allows plants to become strong and productive.
Large, old plants may need to be dug and divided. Early spring is the best time to divide rhubarb plants. Dig up plants as soon as the ground can be worked in spring. Divide each plant into sections with a large knife or spade. Each section should have at least two or three buds or shoots and a large section of the root system. Replant immediately. Set the divided sections in the ground at the same depth as they grew previously.
Follow good cultural practices, such as the removal of flower stalks, fertilizing and watering, to promote plant vigor.
When should I stop harvesting rhubarb?
Gardeners should stop harvesting well established rhubarb plants in mid-June in Iowa. Continued harvest through the summer months weakens the rhubarb plants and reduces the yield and quality of next year’s crop.
Can I harvest rhubarb in summer?
If the rhubarb plants are vigorous, pulling a few stalks and preparing a dish for a special occasion in summer shouldn’t be a problem. Harvesting rhubarb in summer should be a one-time event, not a frequent practice. Continued harvest through the summer months weakens the rhubarb plants and reduces the yield and quality of next year’s crop. In general, it’s best to stop harvesting rhubarb in mid-June in Iowa.
There is an erroneous belief that rhubarb stalks are poisonous in summer. The stalks will likely be a little tougher than those harvested in spring, but they are not poisonous. Plant vigor is the reason that rhubarb should not be harvested in summer.