September 2013 issue of the Cornell Flower Bulb Research Program Research Newsletter:
The 2013 field growing season in Holland was significantly colder than usual. When I was in Holland in May (week 21), tulips were flowering together that are normally never in flower at the same time. Mid season and late season cultivars were all doing well and, for the flower admirer, it was great. But, the late spring and continuing cool summer temperatures have led to a late maturation and late harvest season. Consequently, G stage will be up to 3 weeks later than usual, which in turn, leads to a later date when a tulip bulb can flower properly.