Hello Keith,

Based on what I read below - Switchgrass should be seeded between May and mid-June.

PLEASE READ>>>>>>>>>>

Establishment, Management, and Harvest: Switchgrass should be seeded at a rate of 8 pounds of pure live seed per acre. Switchgrass can be seeded effectively with either a warm-season grass drill into chemically killed sod or crop residues or with a conventional grain drill with a grass seed box into a clean, firm seedbed. Though conservation techniques work well, more important factors in establishment success are planting date, cultivar used, seeding depth, and weed control. For conventional field preparation, there are six important characteristics of an ideal seedbed: soil firm-ness below the seedbed, well-pulverized soil on the surface, the absence of clods and puddles, the absence of live resident weed competition, the absence of seeds from competitive species, and a moderate amount of mulch/residue on the surface.

Planting switchgrass into cool soils can be problematic. Cool-season weeds germinate first and can choke out switchgrass seedlings when the soil warms. If cool-season weeds are a concern, consider no-till planting the switchgrass into warmed soil with non-dormant seed. Switchgrass seedlings can compete better in warmer soils with warm-season weeds. A producer should expect slow switchgrass establishment even with non-dormant seed and good planting management similar to that of other native perennial grasses. Switchgrass should be seeded between May and mid-June. If the seedbed is prepared too early, the cool-season grasses and weeds will be strong and competitive by the time the warm-season grasses emerge. If warm-season grasses are planted too late and the weather is hot and dry, the seedlings may not establish quickly. Seeding near these dates allows seedlings to take advantage of the usually moist spring/early summer growing conditions, establish early, and thus take advantage of the longer growing season and better growing conditions. Switchgrass seed is smooth and will flow through a conventional drill. The broadly accepted optimal seeding depth for switch-grass is between 1⁄4 and 1⁄2 inch. Planting seeds excessively deep will likely result in stand failures. From the article:  Switchgrass as a Biofuel for Michigan (E2987) - September 1, 2017 - Author: Suleiman Bughrara at this link: https://www.canr.msu.edu/resources/switchgrass_as_a_biofuel_for_michigan_e29871

Switchgrass Ecotypes and Cultivars (something else you should know): As switchgrass evolved across North America, various ecotypes emerged with genetic and morphological characteristics that provide a good fit to a particular place. Thus ecotypes in the South typify Southern characteristics, such as long-season growth and subsequent high dry matter yield, given favorable growing conditions. Two major types have emerged through natural selection. The upland types favor drier soils and fare better in semi-arid climates. The lowland varieties grow better in heavier soils and are found where water availability is more reliable. The lowland cultivars have the genetic capability to produce more dry matter than the upland cultivars.

Plant breeders at various agricultural research stations in Texas, Oklahoma, and Nebraska have collected seeds from local switchgrass colonies and released them to form relatively uniform strains adapted to particular locales. These strains, often with some bit of uniformity achieved through artificial selection, are then registered as cultivars. This simple selection program has created the many switchgrass cultivars available today.

Switchgrass cultivars should therefore be chosen on the basis of ecotype (whether an upland or lowland variety) and the latitude of origin. Check with your local Michigan State University Extension office for varieties adapted to your area. Our limited research in Michigan has found Carthage and Cave-in-Rock to be the highest yielding cultivars in a two-year test in East Lansing with total two-year dry matter yields of 18 and 17 tons/acre, respectively. Because switchgrass seed varies greatly in purity and germination, it is often sold on the basis of its "pure live seed" (PLS) percentage. Seed lots with equal amounts of PLS may differ in their volume of bulk seed. Consider this when calibrating seeding equipment. Seed from newly harvested switchgrass can have a high percent dormancy. Acceptable germination levels are often achieved after one year of storage.

Switchgrass Cultivars

Trailblazer . . . . . . . . Upland

Blackwell . . . . . . . . . Upland

Cave-in-Rock . . . . . . Upland

Pathfinder . . . . . . . . Upland

Carthage. . . . . . . . . . Upland

Alamo. . . . . . . . . . . . Lowland

Kanlow . . . . . . . . . . . Lowland

Summer . . . . . . . . . . Lowland

Also from the article: Switchgrass as a Biofuel for Michigan (E2987) - September 1, 2017 - Author: Suleiman Bughrara at this link: https://www.canr.msu.edu/resources/switchgrass_as_a_biofuel_for_michigan_e29871

Hope this helps!!