One key difference between winter and spring wheat is that winter wheat needs to vernalize to trigger the transition from vegetative to reproductive growth. This accumulation of cold units occurs when soil and ambient temperatures are roughly between 32 and 50°F. Last fall was very dry, and despite seeding the winter wheat on time, the seed lay in dry dirt for several weeks. Several of you have asked whether this winter wheat would have vernalized to produce grain this season. Ideally, you want to accumulate those cold units in the fall after seeding, and a seedling, even if it has not reached the soil surface yet, accumulates those cold units. That accumulation will continue in the spring if needed.
Source : umn.edu