Dividing and Thinning Rhubarb
Rhubarb can propagated by planting pieces obtained by dividing the crown. Pieces are taken from 4-5 year old crowns. You can divide earlier if you desire more plants. Dividing can be done either in the spring or the fall with equal success, but I have found early spring is best. I wait until early growth is just starting so I can see where to best divide the root mass. Dig up the crowns and roots being careful not to damage the crown. Cut the roots into 4 to 8 pieces. It is recommended to split dormant crowns between large buds or "eyes" so that at least a 2-inch cross section of storage root is left with each bud. Be careful of is not to break off the delicate buds which are easily broken, but otherwise the roots are quite tough and will tolerate quite a bit of rough handling. Very small buds will give small plants for the first few years after planting, while four to ten new roots can usually be obtained from crowns that have been grown a few years. Root pieces should be protected from drying or freezing if they are not to be planted immediately. When dividing crowns for re-planting, it is important to mark the vigorous plants in June and use them as planting stock the following spring. Crowns should not be divided from diseased plants.
Step by Step: Dividing A Rhubarb PlantThis (below) is the original plant last summer (1996). It is 4 years old. It doesn't really need to be divided but I want to move it to a different location so I will take the opportunity now. As shown here the plant is over 3 feet (90 cm) in width and the leaves are about 1 foot (30.5 cm) across. This plant is the Victoria variety which produces very green stalks and grows rather vigorously and quite large.
You can divide rhubarb with equal success in either early spring or late fall. Shown here is the plant in early spring (mid March) 1997. Spring came early to Maryland this year so the rhubarb is growing already. This makes it easier to divide but I think its more stressful on the plant. Next time I will divide them in the late fall. The early growth shown here is about 6 inches (15 cm) tall.
For the first division I simply use a shovel to cut through the root/rhizome cluster between the "buds" of new growth. Careful study of the cluster will reveal old, rotten, rhizome and roots. This is a good area to cut through. After I separate the 2 clumps I repeat this several times. Each new plant will have a small rhizome, some roots, and a "bud" of new growth (because its spring).
I have now divided this into eight new rhubarb plants. Some are large chunks of rhizome, others are just little root/rhizome/bud slivers about 3 inches (8 cm) in length. All of these will grow into mature, healthy plants if properly re-planted.
Before I re-plant the divisions I examine the rhizome/root area for excessive rot and decay. If there is a significant amount I would discard this division. Here there is very little rot and I cut that off. There will usually be some rot as this is part of the normal growth of the plant. You can also see how large the rhizome/root mass is. Some old (10 years old more more) plants can have root masses that are 3 feet (90 cm) in diameter and 1 foot (30 cm) deep. This is a young plant by comparison.
Here is one of the divisions in its new home. Notice that I have planted it in a mixture of garden soil and compost (50%). Rhubarbs like compost! Be sure to water well and check frequently. I will cut off the largest leaves on this division as they will only drain the strength from the plant and they will probably wilt and rot anyway. The new plant needs its strength for developing new roots.