The University of California says it right when they say “if plants flower when we want them to, we cal it blooming. But if plants flower when we don’t want them to, we call it bolting. Flowering is an undesirable train when growing rhubarb, therefore bolting describes the event.” Rhubarb flowering is just a part of the plant’s life cycle, where it can produce seeds for reproduction. But, this process also takes away from the plant’s ability to produce edible stalks (and the seedlings grown from those seeds are usually less desirable than the parent plant and more likely bolt).
So, why does a Rhubarb plant bolt?
Some selections are more prone to bolting than others. Victoria and MacDonald are heavy seed stalk producers. Canada Red and Valentine are less likely to bolt. Buy only named, vegetative propagated varieties, or get divisions from another gardener who has a high quality planting.
Plant maturity. Mature plants are more likely to bolt than younger ones. Dividing the crown every 4-5 years helps to rejuvenate the planting.
Excessive crowding. Rhubarb plants bolt when crowded by nearby plants or the rhubarb plant has gotten too thick itself. When this happens, dig and divide the plant to reduce crowding and allow plenty of room for the rhubarb to grow.
Low Nutrients. Feed regularly every spring with a balanced fertilizer like formula 49 and composted manure.
Weather. Rhubarb prefers cooler temperatures. So when plants are stressed due to drought and hot temps, poor nutrition, they produce thin leaf stalks and lack color.
What to do? Rhubarb may bolt for one or a variety of reasons (as listed above). If it happens, simply remove the flower stalks as soon as you see them appear. If another comes up, clip it off as well. Keep it up, and eventually the plant with stop flowering and start growing as it should. By the way, flowering does not make the stalks poisonous. They are edible with or without flower stalks. But, the leafy portion of the plant is always poisonous. (If you grow the Rhubarb for ornamental reasons and like the flower, let it flower, just remove the flower before it sets seed.)
Plant Rhubarb in the spring (in ground or in containers) Plant in a well drained location with ¾ day to full sun. Always use a starter fertilizer like Master Nursery Master Start or Dr. Earth Starter Fertilizer. Space plants about 30 to 48 inches apart, with the crown about 1-2 inches below soil surface. Dig a wide hole and amend the soil with Master Nursery Gold Rush or Bumper Crop. Feed well with a well balanced nitrogen fertilizer like Formula 49. Water in well/water as needed. Rhubarb grows best in fertile, well drained, loamy soils (pH best at 6-6.8). Water as needed during drier times. This is very important. Feed Rhubarb in the spring with a balanced fertilizer or rotted. Mulch heavily (placed around the plant) in the spring and late fall. Allow plenty of room to grow, with no competition from other plants (or weeds). Plantings have been known to remain productive for 8-15 years. If you have any questions or concerns regarding rhubarb, please contact one of our excellent employees and they will be more than willing to help you.