 In the northwestern US states of Oregon and Washington, there are typically two harvests, from late April to May and from late June into July; half of all US production is in Pierce County, Washington.Rhubarb is ready to consume as soon as harvested, and freshly cut stalks are firm and glossy.Rhubarb damaged by severe cold should not be eaten, as it may be high in oxalic acid, which migrates from the leaves and can cause illness.