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Monday, March 25, 2019

Propagating Rhubarb

Rhubarb can be propagated by several means: Dividing the root mass, growing rhubarb from seeds, or by Tissue Culture. Of course, you can always purchase rhubarb plants or rhizomes ready to plant in your garden. See the list of sources for a few of the mail order companies that sell rhubarb.
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 Plant

This (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.

Dig up the root ball being careful to not destroy too many roots. Shown here is the same plant as immediately above. you will notice that some of the roots extend from the rhizome for 16 inches (40 cm) or more. You can't help but break some of these, but that's ok. Here I show you where I plan to make the first division. This plant has two major clumps of "buds". You can see this by looking at the clumps of petioles (stems). There are 8-10 possible plants here if I divide carefully.

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.

Rhubarb Tissue Culture

Rhubarb is often commercially propagated by tissue culture. The Kentville Research Center has been the site of research on propagation of rhubarb. The current interest in growing rhubarb on a commercial scale has been stimulated by increasing demand for it, but growers are faced with two difficult decisions: What are the best varieties? Where can healthy planting stock be found? The Kentville Research Center is providing assistance through the technique of micropropagation which consists of starting test tube cultures from minute growing tips (meristems). These meristems are dissected out of buds and when provided with proper nutrients and plant hormones will grow and multiply. The benefits of this propagation technique include disease free plants and year round rapid multiplication. Rhubarb micropropagation techniques are now available for commercial tissue culture labs to exploit and rhubarb growers can look forward to a secure supply of healthy plants.

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