Perennial grasses are physiologically capable of being grazed after they reach the three and a half new leaf stage. Correct determination of grazing readiness by counting grass leaf stage requires a rudimentary understanding of how grasses grow.
Grass tillers are produced vegetatively from axillary buds. Each tiller lives for two growing seasons. During the first growing season, grass tillers remain vegetative and produce 6 to 8 leaves. During the second growing season, grass lead tillers produce a second set of 6 to 8 leaves plus the development of flowers and seeds.
At the end of the growing season, all tillers deactivate the chlorophyll and turn a tan color. Lead tillers that had produced flowers are terminal. Vegetative tillers that had produced only leaves remain alive through the winter by burning stored carbohydrates.
Early the following spring, chlorophyll is reactivated in parts of the previous years leaves where the cells did not rupture. Usually, each carryover tiller has 2 or 3 previous years leaves that are half tan with ruptured cells and half green with complete intact cells. These green chlorophyll portions photosynthesize the material that will produce the new current years leaves.
New leaves of these lead tillers grow straight up from the apical meristem at the tillers base through the old leaf sheaths until it reaches full size, then it tips to one side of the tiller. The next new leaf will tip to the other side of the tiller when it reaches full size. The second year lead tillers will reach the 3.5 new leaf stage when they produce three new full size leaves with a fourth new leaf about half size and still growing straight up. The old carryover leaves that are drying but still attached towards the bottom of the lead tiller are never included in the count of new leaves.
Perennial grass leaf growth stage of second year lead tillers is a dependable method to determine grazing readiness because development of the number of leaves is determined by the length of daylight. The leaf length and weight can be slightly modified by temperature and precipitation and will be variable from year to year.
Each perennial grass species has a different but consistent date, within 3 days, each year that they reach the 3.5 new leaf stage. However, poor management practices that remove an extensive portion of the viable carryover leaf material can greatly delay the time that lead tillers develop 3.5 new leaves.
Cool season native grasses reach the 3.5 new leaf stage during late May or early June. The recommended grazing start date for native rangeland is 1 June. Warm season native grasses reach the 3.5 new leaf stage by mid June.
Crested wheatgrass reaches the 3.5 new leaf stage on 22 April, earth day, but does not have sufficient leaf material to graze until early May. Smooth bromegrass reaches the 3.5 new leaf stage by early May. The recommended grazing start date for domesticated cool season grass complementary spring pastures is 1 May. There are no perennial grasses that reach grazing readiness growth stage earlier than 1 May.
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