Here’s what we found from a couple of sources:
Switchgrass should be harvested with conventional haying equipment after the top growth has completely died back. This will occur from mid- to late October in most regions, according to a USDA grant-funded entity called the National Sustainable Agriculture Information Service.
A single harvest of switchgrass in late fall or early winter results in the highest sustainable biomass yields and good stand persistence from year to year, several studies have found. Moisture should be 15% or less to facilitate quick baling and transport, and to ensure a higher-quality feedstock. Switchgrass co-fired in coal plants is burned at 12-13% moisture. Contact the processing plant to determine the size of bale it will accept. Many research programs have utilized 3 x 4 x 8’ rectangular bales with some success, as these are easier to transport than small squares. Be sure to leave about a 6” stubble after harvest. Forage research has shown that leaving stubble helps to trap snow, thereby protecting the root crowns from winterkill.
For more on using switchgrass as a bioenergy crop, visit: http://www.attra.org/attra-pub/switchgrass.html#establish