Summer annual forage crops — like sudangrass, millets, cane, and sorghum-sudan hybrids — are hot weather crops. And when I say hot weather, that means not only that they grow best in hot weather, it also means they can be injured or even permanently stunted by cool weather.
So, even though you might finish other planting early and it seems summer is already here, don't plant summer annuals too early.
Always wait to plant summer annual forage grasses — any summer annual forage grass — until soil temperature remains permanently above 60° F. For millets soil should be at least 65-70°. That would be late May at the earliest, early June in many cases.
Not only that, air temperature also must remain warm, even at night. If either soil or air temperature gets too cold, the summer annual grass can be stunted permanently, no matter how nice the growing conditions are later on.
True sudangrass might tolerate cool temperatures best of all summer grasses. Generally, if soil stays above 55 ° F and air temperature gets no lower than 40°, sudangrass eventually will recover from the cold stress. On the other hand, millets and some forage sorghums will never snap out of the stress caused by a 45° drop, maybe even a 50° night.
So don't rush to plant summer annual grasses. Even if they don't get stunted, the few days you gain for earlier grazing is pretty small compared to the risk of losing most of their growth potential.
Bruce Anderson
Extension Forage Specialist
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