Time to Plant Summer Annuals

Summer annual grasses, such as sudangrass and millet, can provide supplemental forage during the hot summer months as the growth of cool season perennial grasses slows. These grasses can yield 3 to 5 tons of highly digestible dry matter per acre even under droughty conditions! Now is the time to be planting these heat loving crops, but before you do, make sure you’re seeding at an appropriate rate…

What seeding rate do I use?

In the northeast, most farmers use a multi-cut or multi-graze system for harvesting summer annuals. If seeding in early-mid June, two to three harvests can typically be taken. Seeding rates aligned with a multi-harvest system should be implemented to achieve the best yield and quality.

In addition, seed size and therefore seeds per pound can be highly variable between species and varieties. Hence, summer annual seeding rates should actually be based on plants per acre rather than just pounds of seed per acre. For a multi-cut system, King’s Agriseed recommends seeding for a target of 600,000-650,000 plants per acre for sorghum sudangrass and 650,000 to 700,000 plants per acre for sudangrass. Based on the seeds per pound, Table 1 shows the seeding rates in pounds per acre that would be needed to attain the target population.

Table 1. Seeding rate adjusted for seed size, from King’s Agriseed.
Image 1. Seeds of two sudangrass varieties.

You can see that this ranges from 20-60 pounds! Image 1 shows two varieties of sudangrass that demonstrate the large differences in size that can occur between varieties of the same species. In this case, the variety on the left had 17,650 seeds per pound while the variety on the right had 28,892 seeds per pound. This means that more seed would be needed of the variety on the left to attain the same population as the variety on the right. If they were both seeded at 40 pounds per acre instead, the variety on the left would be planted at 706,000 seeds per acre while the variety on the right would be planted at 1,155,680 plants per acre!

Making these adjustments can save you money by making sure you aren’t over planting costly seed, and that you aren’t shorting your stand which could result in decreased yields or increased weed pressure. For more information on summer annuals please visit the UVM Extension Northwest Crops and Soils Program’s website for our Research Results webpage, Livestock Forages webpage, the Guide to Using Annual Forages in the Northeast, and more. Happy planting!

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