A word of caution .... and why ERC (other conifers) and plums may be a better long-run option for a road-screen. Lots of excitement over the past couple of years about MG as a screen material. I planted MG and other miscan thus cultivars ... all thought to be sterile. Surprise, surprise, I have offspring popping up 4-10 feet from mother plants. The attached site provides some caution about its use.
https://homeguides.sfgate.com/giant-miscanthus-74644.html
At this site, they say .... Precautions
"It is important to contain and plant miscanthus grasses with care in due to their aggressive and accelerated growth rate. Like bamboo, miscanthus grass reproduces rapidly through an underground rhizome or wind-spread seeds. If not controlled, miscanthus grass, especially wild miscanthus, easily becomes weedy and invasive, popping up in unintended places and displacing other plants. Various cultivars of miscanthus are sterile, and unable to self-seed; therefore there is less of a concern for the plant becoming invasive. Such cultivars include miscanthus “cabaret”, “central park” and “cosmopolitan.” As a perennial it is not essential to replant miscanthus grass each season. Once this plant is established, miscanthus grass continues to vigorously produce for 15 to 20 years. Aggressive pruning each year is necessary to control the size of this plant."
After 5-6 years, any plums you plant will achieve a height sufficient for a good screen and sufficient width to eliminate anyone shooting through it or viewing very much at all. While plums will drop their leaves, they are bushy enough to be very dense and require little or no maintenance after planting. MG, on the other hand loses most of its leaves by February (earlier if lots of snow/wind) and requires substantial maintenance. on an annual basis and every 4-5 years for replanting. MG grows outward in concentric rings (over time the center of the plant dies out) and should be cut off or burned in early spring every spring for best growth. Ideally, MG thrives best if older (10+ yr dead-center plants) are dug up and small sections (1/3 of original plant) are replanted to begin the cycle all over again. Not saying you shouldn't plant MG; just be aware, like many things, it ain't a one and doner!
Here's what the USDA says ....
"Prevent Unintentional Spread
Limited information exists on the invasive potential of giant miscanthus in the United States, for this reason best management practices (BMP) should be used. Establish and maintain a minimum 25-foot border around a giant miscanthus stand to monitor and manage any spread. Cover or otherwise contain vegetative planting material (rhizomes) during transportation, planting, and harvest operations when outside the boundary of the production field. When planting or harvesting operations are complete, inspect and remove all residual vegetative material from equipment. Any excess live planting material or material that has the potential to produce a plant should not be disposed of at field edges, field borders, in farm “trash” piles, or in landfills. This material should be hand planted or disposed of in a manner that follows the guidelines in Planting and Managing Giant Miscanthus as a Biomass Energy Crop, Technical Note No. 4 – July 2011."
