Douglas County Extension Office

A sure sign of spring are the calls from people concerned about the safety of their rhubarb plants. This year’s early spring and nice temperatures have allowed rhubarb to grow vigorously, and then the “polar vortex” arrived.  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.

Rhubarb leaves contain oxalic acid, which can be a toxic substance if consumed in large enough quantities. That’s why we do not eat the leaves of rhubarb, as they are high in oxalic compounds. When rhubarb plants are exposed to frost, some of the oxalic acid can travel from the leaves down into the stalks, but there are obvious clues when this happens.

Many universities have studied this, issued recommendations and agree on the following:

• If stalks become limp after frost, don’t harvest them. Instead pull and discard.
• If leaves show damage from frost, such as blackened edges, water-soaked frost injury, etc., pull and discard the stalks, even if the stalk itself is firm.
• If stalks and leaves appear normal after a frost, the rhubarb is safe to eat.
• If stalks and/or leaves are damaged, resulting in needing to pull the damaged stalks, all future regrowth is safe to eat.
• If in doubt or you’re hesitant, just don’t use it.
• Any time rhubarb is harvested, the stalks are better gently pulled, rather than cut.

Rhubarb usually begins to grow in late April in the Upper Midwest. And because our region’s final frost is often mid-May, rhubarb plants have been getting frosted since pioneer days. And unless it’s obviously damaged, rhubarb stalks have been making pies and sauce each spring, even after the common spring frosts.

So, harvest away and enjoy your rhubarb.

If you have other garden questions, please call 320-762-3891 and leave a message, or email me at trot0053@umn.edu.  I check my phone messages multiple times a day and am always near my computer to receive emails.  Also, visit the Douglas County Master Gardeners Facebook page at: https://www.facebook.com/dcmastergardener/ for garden updates, and virtual events.