Miscanthus species are tall, woody, perennial, rhizomatous grasses. Rhizomatous grasses retain a large proportion of the nutrients in the rhizomes, retaining little in the biomass, so nitrogen and nutrient requirements are very low.
Although they are not native to the UK, originating from Asia, under UK conditions miscanthus has been shown to give very high yields (14 oven dry tonnes per hectare per year (odt). The calorific value of miscanthus is slightly lower than that of most wood, and the ash content quite high, similar to straw.
Miscanthus can be planted by rhizome division, and this is the preferred way, though it makes establishment expensive. Conventional agricultural equipment, such as a potato planter, can be used, although specialized equipment has been developed.
Miscanthus is planted in spring and grows strongly to 1-2m by late August. From late July the crop starts to dry out so that when it is harvested in late winter, most of the leaves have died back, leaving canes of 10mm diameter and relatively low moisture content. This first year’s growth gives poor yield, but in subsequent years gives greater height (typically 2.5-3.5m can be achieved) and yield increases over the first 4-5 years. Once established, a miscanthus plantation can be harvested annually for 15-20 years before needing to be replanted.
Yield depends on sunshine, temperature and rainfall, but miscanthus grows well on a range of soils.
Harvesting is undertaken with a modified forage harvester, and moistures below 20% are easily achieved at harvest and can be left to dry further, in the swath, prior to baling. The crop is then baled using a conventional baler to produce rectangular or round bales, depending upon the requirements of the application.