With the several cultivars of lavender beginning to bloom in southern Ontario, I thought it was a good time to provide a refresher on harvest timing and harvesting practices. Harvest timing depends on the end use of the product.
Bundles and Buds
For many products involving buds or whole flowers (e.g. flower bundles and buds), the best time to harvest is when the first buds begin to open on the majority of flowers. This is when the buds and stem have fully formed, but the flower petals have not started to die and turn brown (Figure 1). Flowers harvested for fresh bundles may need to be more advanced for optimal colour. The longer harvest is delayed, the more dead petals there will be and this will result in a less marketable product. Buds will still have a good scent later in the flowering period, but would be more useful in products in which they are not visible such as pillows and sachets.
For both flower bundles and products that require buds, the first step is to harvest with the stems as long as possible. The harvested stems will usually include one pair of leaves at the bottom that can be stripped off after drying with bud cleaning equipment or by hand. Bundles are usually approximately 2.5 cm (1 in.) in diameter when held tight. Wider than this and they may not dry fast enough to prevent fungal development within the bundle. They should be tied with an elastic band. If they are tied with anything inflexible, the flowers may fall out of the bundle as the stems dry and shrink. These bundles should be moved to a dry, warm and well-ventilated area as soon as possible and hung upside down to dry.
Unless customers are explicitly told that products are not to be used for culinary use, consider all bundles as potential food and handle accordingly. A customer may purchase a dried flower bundle and then decide to harvest the buds for culinary use later on. Bundles need to be hung in a clean area that is free of animals or anything that may contaminate the buds. Consider that the buds will not be washed before use, may not be cooked, and that drying does nothing to remove food safety threats. Throughout the postharvest process, identify and correct all potential contamination sources such as dirty equipment, unwashed hands and unsanitary work areas. For advice on specific practices to ensure a safe product email OMAFRA Food Safety experts at email@example.com or call the Agricultural Information Contact Centre at 1-877-424-1300.
For oil distillation, oil quality and quantity peaks at or just after full bloom (i.e. when half of the flowers have either open or senesced). Quality will then gradually degrade, but good quality oil can still be distilled even after the bloom period is completed. This is an advantage for agritourism operations that require the lavender to be in bloom in the field as long as possible before being harvested. Some varieties will begin to shed buds easily after bloom is completed, so oil yield may also decrease after peak bloom. Oil quality will degrade faster under humid and wet conditions that can lead to rot of buds in the field once bloom is complete.
Our research has shown that it is best to harvest lavender buds with some stem material. The stems help to ensure a path for steam to penetrate through all the tissues during distillation and pick up more oil. Usually about 20 cm (8 in.) of stem is sufficient. Growers need to balance speed of harvest with oil quality considerations, so this is not something that requires perfect measurement. It is usually roughly equivalent to the one width of a hand under the flowers if harvesting by hand. If there is a need to distill the product long after harvest, it will be necessary to bundle the flowers and dry them as described for bundles and buds above. This will require longer stems so they can be properly bundled. It is best to avoid picking up too many leaves on the stems, because these will degrade oil quality somewhat.
Drying the flowers for a few hours in the field prior to distillation will allow for more flowers to be distilled per batch because of the reduced moisture content in the stems, but this is not necessary. It is best to distill the flowers the same day as harvest to reduce the degradation of the plant material. If flowers need to be stored for a day or two, they should be stored in a cooler. If they need to be stored for longer periods, they should be dried in bundles where they can keep for months with less degradation of the oil. If it is only a week or two before distillation will occur, there is the potential to leave the flowers in the field until you are ready to harvest, which will cut down on labour requirements but may lower quality slightly.
Regardless of when the flowers are harvested, it is best to prune plants soon after harvest, when labour permits (i.e. within a couple of weeks of harvest). This will give the plant the maximum amount of time to recover and grow before winter. If you let the plants produce new shoots before pruning, you may stress the plants that are already stressed by harvest by forcing them to produce new growth twice within a few weeks. Plants should also be fertilized and watered right after harvest to encourage new growth. If plants are really leggy and you need to do a hard pruning to get them back into a good shape, this may need to be delayed a few weeks to ensure the plant is healthy enough to recover from hard pruning. About 1/3 of this year’s green growth not including the flower stems should be removed for a normal pruning. If there is vigorous new growth by mid- to late-August, another light pruning may be necessary to get the plants back into a rounded shape.