Crown hydration damage on annual bluegrass putting green. Green patches are creeping bentgrass.
Crown hydration is the most common and destructive type of abiotic winter injury, and usually occurs in late winter following periods of thawing and freezing. During late February and March, temperatures often rise above freezing for a few days at a time. When this happens, some turfgrasses (most notably annual bluegrass and perennial ryegrass) begin to deharden and crowns become hydrated. If a rapid freezing event follows the thaw, ice forms inside the crowns of hydrated turfgrasses and either ruptures cell membranes (when ice forms inside of cells), or draws moisture out of cells (when ice crystals form between cells).