Harvest rhubarb through mid-summer, then allow the plants to grow foliage for energy absorption. Cut off any late-summer flower stalks because these waste plant resources.
Mulch the rhubarb plot after the first frost of the season, when temperatures drop to 40 to 50 degrees F. Once the foliage dies, cover the crowns with 2 to 3 inches of straw, wood chips, bark or dried leaves for protection. Lay landscape blankets on top of the mulch in zones 3 and 4 for additional cold protection.
Remove 1 to 2 inches of mulch in spring. Mix the remaining mulch into the soil around the plants for additional nutrition and soil drainage. Put the plants back on their spring and summer water and nutrition schedules for continued growth.