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Growing Rhubarb

Deer Resistant: Deer rarely eat rhubarb!

By: Sandy Feather 2009
Penn State Extension


Q. I have wanted to grow rhubarb for years, remembering the huge plants in my mother's garden and the great dishes she made from it. I researched it on the Internet, and after learning that it is pretty easy to grow, I planted two large, healthy plants. As soon the leaves on one plant reached a good size, they were eaten by what I think were caterpillar of some kind. It eventually died from the infestation. The other one seemed to sustain some damage as well, so I dug it up and grew it in a container on my porch. I did not harvest from it, after reading that you should not for a season or two to allow it to mature. It was gorgeous by the end of the season, but I was unsure how to overwinter it. I asked a local garden expert how to overwinter it, and was told to bury the pot, which I did. When I uncovered it this season, it appeared to be dead. Just in case, I have moved it back to my porch, but still see no signs of life in it.

I would still like to grow rhubarb, but am afraid to plant it in my yard for fear that whatever ate the other plant will kill a new one too. I have an old crabapple tree and an old pear tree, as well as other plants in my yard that were planted by the previous owner. Could they be harboring something that attacked my rhubarb? I would be happy to grow it in a container, if you can give me better advice as to how to overwinter it.

A. Rhubarb (Rheum rhabarbarum L.) is a cool season, perennial vegetable grown for its piquant leaf stalks used in pies and other dishes. You are correct that they should not be harvested in the first year after planting. You can enjoy a few stalks during the second year, and begin regular harvesting from the third year on. Never harvest more than one-third to one-half of the plant stalks so that the remaining leaves and stalks and can sustain the crown of the plant. You can harvest from late May through June. The stalks get too tough to enjoy beyond then.


Rhubarb Leaves are Toxic

Rhubarb's leafstalks are edible, but the leaves themselves contain oxalic acid crystals and are toxic. An adult weighing 145 pounds would have to eat about eleven pounds of rhubarb leaves for them to be fatal. However, a much smaller amount would cause a painful burning in the mouth and throat, gastrointestinal distress, and even convulsions. The oxalic crystals make the leaves unpalatable to most pests, and even deer rarely eat it.

 


Best Soil Conditions for Rhubarb

Rhubarb grows well on most soils as long as they drain well. It is at its best on fertile soils with a high organic matter content, exposed to full sun. Since it is perennial, rhubarb should be given its own space in the vegetable garden where it will not be disturbed by tilling activity in preparation for annual vegetables such as tomatoes, pepper and beans.

rhubarb leaves

Although you can grow rhubarb in a large container, it will grow bigger and better if you plant it in the ground. Your containerized plant may have died over the winter because too much moisture accumulated in the pot and caused the roots to rot. Ice may have formed and blocked the drainage hole(s), which can happen when you sink potted plants in the ground for the winter. If it had been planted in the ground, excess water could have drained away more easily.


Common Rhubarb Pests

The most common pest of rhubarb in our area is the rhubarb curculio, This pest damages rhubarb by feeding on leaf stalks and the edges of the leaves (weevil damage is known as "notching"). Disease-causing organisms can invade these feeding wounds, and cause rhubarb plants to collapse.

The adult rhubarb curculio is a large, grayish-brown beetle with a prominent snout. It appears to be dusted with a yellow powder that rubs off easily. They overwinter as adults in garden debris or piles of leaves, and become active mid- to late June. They can be seen on the stalks and leaves of rhubarb, dock, thistle or sunflowers. They hollow out shallow cavities in the leaf stalks of rhubarb and other host plants, where they lay a single egg in each cavity. Eggs hatch in seven to ten days in most host plants, although eggs laid in rhubarb plants are usually crushed by the actively growing stems and do not survive to maturity. The yellowish-white larvae appear as legless grubs with brown heads, and they burrow down through the leaf stalks of host plants, exiting through the base of the plant just below the soil surface. It takes about two months for them to mature. Then they pupate in a cavity at the base of the host plant, and emerge as adults to feed briefly before searching out a sheltered site to spend the winter. It is helpful to eradicate host weeds such as dock (especially curly dock) and thistles in and around the garden to avoid problems with rhubarb curculio. The easiest way to get rid of the adults is to handpick them and crush them as you find them on your rhubarb. We only have one generation of this pest annually, and adult activity ceases by mid-summer. If you eradicate other host plants by July, you should not be bothered with the newly hatched adults. Be sure to burn them or send them out with the trash if there is a chance they contain rhubarb curculio larvae.


Slugs on Rhubarb Leaves

Slugs (during wet weather), Japanese beetles and potato leafhoppers can also damage rhubarb. You mention that you thought it was a caterpillar. There is a stalk borer whose immature stage is a caterpillar. Their eggs are laid the previous fall on weeds and grasses near rhubarb plants where they hatch the following spring. The caterpillars migrate to rhubarb where they tunnel into the stalks and can cause serious injury. Controlling weeds and mowing lawn areas near the garden can remove their breeding sites and reduce or eliminate injury from this pest.  Yellow woolly bear caterpillars (they look just like sound) can also feed on rhubarb plants. These pests can also be handpicked and destroyed to protect your rhubarb. It wouldn't hurt to wear gloves because caterpillars often have stinging hairs on their bodies that cause dermatitis in susceptible individuals.

rhubarb

It is fairly uncommon to lose rhubarb plants to major insect infestations. Go ahead and try another plant or two, and plant them out in the garden. Scout them at least weekly, and handpick any insect pests you find on them. It is not impossible that you have some plants in your yard that are host to whatever damaged the first rhubarb plant, but insect outbreaks are often cyclical. You should have better luck this time around.

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