Is rhubarb a vegetable? A fruit? An ornamental plant? It’s a very ornamental vegetable that is usually prepared and eaten much like a fruit. All that and it’s perennial in many areas. Rhubarb is a cool season crop that is grown for its fibrous leaf stalks, which are a wonderful sweet-tart treat.
Rhubarb is a big, leafy plant, growing 2 - 3 feet wide and tall. It is grown for its leaf stalks but makes a beautiful, ornamental plant, especially the red and yellow varieties. Many people prefer the red varieties for their taste and tenderness, although the green varieties tend to be a bit more productive than the red.
Only the stalks are edible. The leaves themselves are toxic and are removed at harvesting. The leaves contain a substance called oxalic acid crystals, which are toxic to people and animals and can result in poisoning. (See full Caution below.)
Rhubarb does best in cooler climates because it requires temperatures below 40 degrees F. to break dormancy and stimulate bud growth. Rhubarb can be grown as an annual in warmer areas that get some winter cold if you start seeds in the late summer/fall and move the plants out early the following spring. However, too much heat causes rhubarb to have thin stalks and leaves
CAUTION: Only the stems and ribs of the leaves are edible. The leafy portion is toxic to humans and other animals. Further, rhubarb damaged by frost may become inedible. If the stems are not firm and upright, do not eat them. Frost damage can cause the oxalic acid crystals to move into the stalks. You can still compost rhubarb leaves, even though they are slightly toxic if ingested. The oxalic acid crystals dissipate in the soil long before they are absorbed by other plants.
Mature Plant Size
Most rhubarb plants grow about 2 - 3 feet wide and tall, depending on the variety
For the healthiest rhubarb plants, give them a spot in full sun. The red and yellow varieties will not attain full color without full sun.
Days/Years to Harvest
As with most perennial crops, don’t harvest any rhubarb at all their first year, to allow the plants time to become established. You can take a small harvest in the second year. During the 3rd year, you can harvest for about 1 month. After the 3rd year, you can harvest whenever there are stalks ready for picking.
If you are gardening in a warm climate and growing rhubarb as an annual, you can harvest all you want the first year, since you don't have to worry about the plants surviving a second year.
The main harvest season is spring. Smaller harvests may continue throughout the summer, weather permitting,
Rhubarb Growing Tips
Soil: Rhubarb prefers a slightly acidic soil pH of 6.0 to 6.8. Since you’re growing it for the foliage and it has a short season, you want a soil high in organic matter, to support quick spring growth. Care should be taken when preparing the rhubarb bed since the plants will be there for quite awhile after.
Planting: Rhubarb is usually grown from purchased crowns (rhizomes and buds). You can divide existing rhubarb plants (root balls) or even start them from seed, although they might not grow true to color. When growing from seed, it can take 2 years longer before the plants are large enough to harvest.
Space rhubarb crowns every 3 - 4 feet in rows about 3 feet apart. If planted too closely, the plants will be smaller and less productive. You can plant in a long trench, much like asparagus, or dig individual holes. Place the crown 2 inches below the surface of the soil. Firm the soil gently and water well.
Rhubarb likes regular water, although mature plants are quite drought resistant.
Remove flower stalks as soon as they appear. Flower stalks are rounder, thicker and taller than leaf stalks. If allowed to mature and flower, the leaf stalks will be thinner.
Rhubarb does not like competition from weeds. A 2 - 3 inch layer of mulch will suppress weeds as well as help conserve water.
As with most perennial vegetables, don’t harvest the first year. Allow the plant to hold onto its leaves and build its strength. A top dressing of manure will keep it going.
You can take a small harvest the second year. Harvest stalks that are at least 1 inch thick and leave the rest. During the 3rd year, you can harvest for about 1 month. After the 3rd year, you can harvest whenever there are stalks ready for picking. Plants can remain productive for 8 to 15 years, unless affected by pests or diseases.
To harvest, cut the stalks at the soil line or pull out individual stalks as needed. You can harvest the whole crop at the same time or harvest in succession over a 4 - 6 week period.
As the temperature warms, growth slows and may even go dormant, but will resume in fall as temperatures fall.
Caring for Rhubarb Plants
Dividing Rhubarb: Plants will need to be divided or trimmed every 4 - 5 years. You will notice the stalks getting thinner as the crown becomes overgrown and crowded. When this happens, either divide or trim the crown to 4 - 5 buds.
To divide rhubarb, dig the root mass and divide the crown between buds or eyes, into pieces about 2 inches long, with roots attached. You can divide in spring or fall, but it’s easier in spring, when the plant is coming out of dormancy and growing new roots.
Rhubarb crowns get very dense and thick. Try to divide about every 3 years, before the crown becomes as dense as a cinder block and impossible to cut through.
Winter Protection: Rhubarb needs a period of cold to remain productive. A layer of mulch over the bed, once the ground freezes, will protect the roots from drying out. Otherwise, the plants should be fine on their own.
Pest and Problems of Rhubarb
Rhubarb plants have very few problems, however there are a handful to watch out for.
- Crowns may rot in wet soil.
- "Foot rot" is a more serious crown rot caused by a fungus. Foot rot will spread to other rhubarb plants. Destroy any affected plants and allow the planting area to dry. You may need to relocate the bed.
- Black spots on the stems are probably rhubarb curculio, a type of beetle.
The Best Varieties of Rhubarb to Grow
- "Victoria" - The green standard variety. A large, vigorous plant
- "Valentine" - One of the most disease resistant
- "Giant Cherry" - Good for areas with mild winters