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nutrients back to the rhizome (Aurangzaib, 2012). Sage et al. (2015) observed
and quantified a similar effect on a new triploid M. × giganteus hybrid
(Nagara) in Ontario, Canada. In this instance 3/4 of the leaf N failed to translocate. Similar effects may be observed for other nutrients.
During winters, especially the first winter, M. × giganteus is vulnerable
to freezing damage. When soil temperature drops below −3°C to −5°C at a
depth of 4–10 cm, rhizomes are killed (Dong et al., 2019; Heaton et al., 2010).
Insulation of the planting with straw, dropped foliage, or other means may
be critical for good establishment in places where such cold is likely. In a
long-term study described by Maughan et al. (2012) and Lee et al. (2017), 75%
of a 2008 summer planting of potted, actively growing rhizomes was lost in
the first winter. These had been greenhouse grown from 25 g rhizomes in
9 × 9 × 12 cm pots so they were much larger than typical plantlets, but were
planted rather late in mid-July. The missing plants were replaced in 2009
(Maughan et al., 2012).
A fall planting of M. × giganteus ~25 g rhizomes at Mimon, Czech Republic,
was fully destroyed by an 8-day February–March period of air minimum
temperatures at −10°C to −18°C and maxima below 0. Soil temperatures were
not determined. Only 1/10 of a previous spring planting in that same location survived (Nebeska D. personal observation).
Kucharik et al. (2013) developed a predictive model for likelihood of winter loss, based on a 30-year climate record across the Midwest US. The effect
of insulation of the crop by straw and leaf matter at various depths was also
calculated. A layer of 5 cm gave significant protection in many regions but the
northern portions of several states near the Canadian border (~49 N latitude)
had a 50% likelihood of losses even with protection. So far as we are aware no
comparable model has been generated for Europe, although it is feasible to do
so. Somewhat surprisingly, in the studies described by Kalinina et al. (2017),
M. × giganteus survived winter even in the vicinity of Moscow, Russia (~55.75
N latitude), because soil temperatures never dropped below 0°C in the winter
of 2012–2013.
Seasonal droughts of varying magnitude have a strong negative effect on
biomass yield, when irrigation is unavailable. Kering et al. (2012) described
this effect in southern Oklahoma where half of carefully pot-grown
M. × giganteus plants died during the 2 months of 2008 following transplantation to a field site, while other biomass grasses had high survival. Biomass
yield of the M. × giganteus never approached that of the other crops over the
study period even though precipitation returned from 58 cm in 2008 to near
average 97 cm year −1 value in the second and third years (130 and 91 cm,
respectively). In Eastern Ukraine, a planting of M. × giganteus failed in 2017
when summer rainfall dropped from an average of 7 to only 1 cm during
July although the annual total was close to the average 45 cm (Stefanovska T.
personal observation).
Failures of timely rain following a 2017 planting at Ft. Riley, Kansas
(~39 N latitude), resulted in loss of ~1/4 of the M. sacchariflorus Bluemel