Lavandins are reaching full bloom in many areas (Figure 1), while angustifolia cultivars are at the end of bloom. Most cultivars are past the best stage for flower bundle harvest, except for fresh bundles of lavandins. Harvest for essential oil distillation can be done at any time now on both types of lavender. Since angustifolias are past bloom, it is best to harvest for distillation as soon as possible. Not only does essential oil quality gradually degrade over time, especially in wet weather, but some cultivars begin to shatter their buds easily and yield potential can be reduced substantially if this occurs.
Figure 1. Closeup of a ‘Grosso’ lavandin flower at peak bloom on July 21, 2017. Note some of the buds are finished blooming with dried petals still attached, some have not bloomed yet, and the rest are in full bloom. Oil yield reaches its peak at this stage, remains at that level to the end of harvest and only is lost with the loss of buds.
Observations from our latest distillation suggest how important it is to pack the distiller properly. When the flowers with stems were evenly spread out and carefully packed to the edges, we had double the oil yield per kilogram of flowers than when the flowers were well packed and spread out but not pressed carefully to the edges of the distiller. If the steam has an easier path around the lavender than through it much of the oil in the middle of the distiller will not be retrieved. Flowers are generally collected in loose bundles when harvested by hand. It is important to break up these bundles so the stems are not all aligned in the same direction. This also could lead to an easier pathway for the steam to go through the stems rather than the flowers.
If you have not fertilized already, now is a good time to add nitrogen to stimulate new vegetative growth. We are just finished the harvest assessment of our nitrogen rate trial on lavender and preliminary analysis of the results shows significant increases in both flower bundle yield per plant and oil yield per plant with increasing nitrogen up to 80-120 kg/ha split into three applications from early June to early August. Plants in higher nitrogen treatments were also greener in the late summer last year and appeared to have less Septoria leaf spot.
The original thought of many growers was that increasing fertility may cause too much vegetative growth at the expense of flowers and that oil yield per flower would also decrease. We have definitely proven that this is false. More vegetative growth in the summer leads to higher flower yield the following spring and oil yield per flower is the same no matter what the nitrogen rate. This lead to higher oil yield per hectare as well. Oil quality was not assessed, but did not seem to be any lower with high nitrogen rates. More trial results will be published once the analysis is complete.
Pruning should also occur shortly after harvest to get plants back into a good shape. One third to one half of this year’s growth should be pruned off. This will promote a sturdier plant that will not split open as easily under the weight of either the snow over the winter or the blooms next spring.