The success of management practices on growing small grains often depends on the timeliness of the operation. To obtain an optimal response to management inputs, cultural practices should focus on crop development rather than calendar date. The figure below illustrates growth stages (GS) of wheat according to the Feekes's scale (growth stages ranging from 1 through 11).
During a typical year in which winter wheat is planted in mid- to late September, the crop initiates tillering or completes GS 1 and GS 2 during the fall. After winter dormancy, during and following greenup, tillers are formed (GS 3), and the crop completes the tillering phase (GS 3 to 5) by late April or early May. Jointing (GS 6), or the appearance of the first node at the base of the plant, indicates the end of the tillering phase and the beginning of stem extension. Stem extension (GS 6 to 10) occurs in May, and a rapid increase in crop height is apparent at this time. In most years, wheat heads (GS 10.1) in late May or early June and flowers (GS 10.5) a few days later. Spring temperatures, however, can alter crop development and heading by two to three weeks. Flowering thus occurs from late May to mid-June depending on spring .temperature. The grain filling or ripening period usually lasts about one month, and the crop is physiologically mature by early to mid-July. Once the grain has dried down to the appropriate moisture, the crop is ready for harvest.
In a typical year, oats and spring barley are planted in April, and tiller initiation (GS 2) occurs in early to mid-May. Spring grains form tillers (GS 3) and complete the tillering phase (GS 4 to 5) during the latter two to three weeks in May. The first node (GS 6) appears at the base of the stem in late May. Stem extension takes place during the next three-week period, and spring grains are heading (GS 10.1) about June 15 to 25. Warm springs, however, accelerate the development of spring grains, and in warm years the first node (GS 6) can be detected in mid-May and heads can be seen in early June. Flowering and grain filling occur earlier in barley than in oats, and barley is usually ready for harvest a few days earlier than oats. Both crops are harvested in August.
Growth stages in small grains. (http://extension.psu.edu/agronomy-guide/cm/images/figure-1-7-2.jpg)