What if my rhubarb freezes?

A sure sign of spring at AnswerLine are the calls from people concerned about the safety of their rhubarb plants. It seems like every year we have a week or so of really nice temperatures that allow the rhubarb plants to grow vigorously. Then the temperatures take a dive and we have a frost or freezing weather.  There is an old wives tale that says rhubarb that has frozen is poisonous and that you should destroy or dig up your plants to stay safe.

That old wives tale is just that; a tale that is not correct.   If your patch of rhubarb freezes, the fleshy part of the plant will freeze.  After a day or two, the frozen leaves and stems will become soft and blackened.  This is a result of the damage that freezing and thawing cause to the plant.  Most people, when they pick rhubarb, are particular and choose the nicest, freshest looking stalks.  They would not choose softened, black, or mushy stalks.  Those stalks should be pulled and discarded; this is something most people would do without thinking.

Remember, only the stalks or petioles should be eaten because the leaves contain moderately poisonous oxalic acid.  It is generally recommended that home gardeners stop harvesting rhubarb in early to mid-June. Continued harvest through the summer months would weaken the plants and reduce the yield and quality of next year’s crop. The rhubarb stalks may become somewhat woody by mid-summer, but they don’t become poisonous. Sometimes we have callers wanting to harvest enough for a crisp or a pie during mid-summer.  We tell them to look for some smaller, tender stalks that could be pulled.  If the rhubarb patch is an older, established patch pulling a few stalks should not cause permanent damage to the patch.

Enjoy your rhubarb.


Liz Meimann

Liz Meimann

I received both my undergraduate and graduate degrees in Food Science at Iowa State University. I love to quilt, sew, cook, and bake. I spent many years gardening, canning, and preserving food for my family when my children were at home.

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15 thoughts on “What if my rhubarb freezes?

  1. This answer is in conflict with the University of Illinois Extension that says that the oxalic acid travels from the leaves to the stalks and then they become toxic. Now I’m wondering who to believe?

  2. If a stalk of rhubarb has frozen, the University of Illinois says that those particular stalks–that will shrivel and turn black after freezing–would not be safe to eat. If you are out in the rhubarb patch, will you choose stalks that are shriveled and black? Or will you choose stalks that look crisp and nice? The stalks that look good are safe. Stalks that look shriveled or black may or may not be safe, but you would never choose to eat those anyway.

  3. Think a clarification is needed here. If the rhubarb is hit with a frost the leaves will wilt and the oxalic acid present in the leaves will migrate to the stalk. Over a few days the entire stalk is likely to shrivel and turn black, however the morning after the frost the stalk may look fine. In a heavy frost or freeze the entire plant will wilt.

    Just how toxic is oxalic acid? Hampshire College reports “Rhubarb leaves contain 0.5-1.0% oxalic acid, so that you would need to
    eat quite a large serving of the sour leaves, perhaps 10 pounds to get a lethal dose. However, a fraction of that could nevertheless cause severe symptoms of oxalic acid poisoning.” http://helios.hampshire.edu/~nlNS/mompdfs/oxalicacid.pdf
    That is the same oxalic acid that migrates to the stalks.

    Every Spring the Help Line will get at least 1 call regarding frost and rhubarb. The recommendation is: if the leaves appear to be wilted due to frost DO NOT use the rhubarb as the oxalic acid will have already begun its migration into the stalks even though the stalk looks fine . Cut the stalks down to the ground and new growth will emerge. In a heavy frost or freeze the entire plant will appear wilted, the stalks will be limp. Again, cut the plant down to the ground.

    Larry Stratton MG
    University of Illinois Extension
    Peoria County

  4. With temperatures in nw iowa expected to drop we harvested some rhubarb and have attempted to cover as well. I was worried as how to know if my rhubarb has frost damage and is toxic. So if we are expected to have frost over the next few nights we need to cover and uncover then wait several days for the actual results ?

  5. Hi, cover your rhubarb at night and uncover it during the day. Know that if the rhubarb gets for us damage or a couple days time so stems and leaves will start to wilt and turn a little black. Don’t pick those to eat, but then again you wouldn’t have chosen those stocks to eat. The whole rest of the plant will not become toxic. Any fresh rhubarb growing after that time will also not become toxic. If you have further questions please don’t hesitate to call us at AnswerLine. In Iowa the number is 1-800-262-3804

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