What to harvest when? Autumn, winter, annual and biennial harvesting of giant reed, miscanthus and switchgrass in northern and southern Mediterranean area

•Giant reed produced more biomass than miscanthus in southern Mediterranean.•6-year cumulative biomasses of switchgrass and miscanthus were similar in northern Mediterranean.•Delaying harvest over winter increased biomass productivity and quality in southern Mediterranean.•Biennial harvesting of miscanthus and switchgrass resulted in lower biomass yields compared to cumulative annual biomass.

Side by side biomass productivities, harvesting time (autumn vs. winter) and frequency (annual vs. biennial) of three perennial grasses were compared under northern and southern Mediterranean climates. Miscanthus (Miscanthus × giganteus Greef et Deu.) was compared to giant reed (Arundo donax L.) in Catania (37°24′N, 15°03′E), and to switchgrass (Panicum virgatum L.) in Bologna (44°55'N, 11°45′E). Generally, giant reed produced about 50% higher biomass than miscanthus in Catania. Miscanthus almost halved biomass productivity in the driest year, while giant reed reduced biomass yield by only 30% under the same conditions. In Bologna, miscanthus and switchgrass produced similar amounts of cumulative biomass over 6 years. Switchgrass kept more stable annual yields than miscanthus, which, however, evidenced a higher potential under favorable climate conditions. Autumn harvest significantly reduced biomass productivity and quality (moisture content, ashes, cellulose and hemicellulose), particularly under South Mediterranean climate. In Catania, autumn biomass was 50% (giant reed) to 85% (miscanthus) lower than winter biomass, while in Bologna, autumn cut reduced switchgrass yield by 20%. Biennial harvesting resulted in almost 40% lower cumulative biomass yield than annual cut, after 6 years.