Production potential and crop agronomy of sweet gale (Myrica gale L.) in the north of Scotland

Sweet gale (Myrica gale L.) is a common shrub in the wetter parts of north-west Europe, north America and Asia. An oil obtained from shoots of Scottish plants has been included in cosmetic products but, as a result of the high costs of wild harvesting, the potential for growing sweet gale as an agricultural crop is being investigated. Six trials, comparing three weed control treatments (no weeding, herbicide and herbicide plus mulch) were planted and monitored at different sites in northern Scotland from 2008 to 2010. Good weed control was critical for plant survival and growth and was most effectively achieved with herbicide plus mulch and this treatment indicates the potential of the crop. By 2010, averaged across sites, plant survival was highest (63%) in this treatment and fresh weight shoot yields (0.75 t ha−1 and 35.4 g plant−1) and oil yield (1.38 L ha−1) were all significantly (P < 0.05) higher than in the other treatments. These yields are higher than those reported for wild harvesting, but at the best site, yields were about 4 times the average, showing the importance of good site selection. Soil water content was significantly (P < 0.05) higher in the mulch treatment down to about 30 cm depth through most of the growing season. Oil concentration was not significantly affected by weed control treatment but, in 2009, was significantly (P < 0.001) affected by site, with site averages ranging from 1.01 to 2.36 μL g−1 fresh weight. In 2009 and 2010, oil concentration was significantly (P < 0.05) negatively correlated with site temperature over the growing season. Studies of shoot growth showed that the rate of leaf emergence was significantly (P < 0.001) correlated with both soil and air temperatures and the relationships suggested base temperatures of 5.2 °C and 6.9 °C for air and soil, respectively.

► Trials at six Scottish sites investigated growing sweet gale as a cultivated crop.
► Site and weed control treatment affected shoot and oil yields.
► Herbicide and mulch gave the best weed control and highest shoot and oil yields.
► Shoot and oil yields at 2.5 years exceeded those reported for wild harvesting.
► Shoot oil concentration was negatively correlated with average site temperature over the growing season.