By McKenna Campbell, Student – Horticulture Research Assistant, and Sean Westerveld, Ginseng and Herbs Specialist, OMAFA
We conducted a small lavender drying experiment at the Ontario Crops Research Centre – Simcoe to determine the best ways to retain bud and stem colour in lavender bundles. Lavender bunches are dried to remove excess moisture, therefore preserving them. Dried buds are often used in the cosmetology and food industries. When added to products such as soap and tea, the characteristic colour and scent need to persist. When consumers purchase bundles as home décor, colour is one of the main characteristics looked for.
Bundles were taken from two Lavandula angustifolia cultivars (‘Hidcote’ and’Melissa Lilac’) as well as two Lavandula x intermedia cultivars (‘Phenomenal’ and ‘Gros Bleu’) at optimal bloom time. The ideal time to harvest lavender for drying is when all the buds are fully developed and about 10% of them are in bloom. Four bundles from each cultivar were stored in various locations around the research station until they were fully dried. When pressure was applied to a dry stem, it snapped, indicating that the preservation process was complete. We used five different drying locations: barn rafters, indoor storage room, forced-air kiln, greenhouse, and hoop house.
A dry, warm spot in our barn rafters was chosen as one of our drying locations because it is typical industry practice. Barn rafters receive regular airflow from outside and warm temperatures, aiding in the preservation process. A dark storage room in the OMAFA building was also used that experiences average temperatures of 26°C, and low humidity. This location provided insight about what a grower could expect while drying bundles indoors. A forced-air kiln on station was selected for its consistent temperature, low humidity, and consistent airflow. Our unit was set to 38°C ± 2°C, one of the lowest settings on our machine. The hoop house onsite was selected because it mimics drying in a ground-level building with good airflow. This location received no direct sunlight but some light, good airflow, and temperatures slightly warmer than the ambient outdoor temperature. There was no humidity control in this location. The greenhouse location provided a very hot (upward of 40°C during the day) and sunny spot that did not receive airflow to dry our bundles. A location such as this could be accessible to growers, sparking our interest in the quality of bundles dried in this spot. All bundles were hung upside down in their respective locations and checked daily.
Once all small bundles in a location were completely dry, they were photographed and made into a large bundle containing 100 stems. These large bundles were then compared. After random labeling, random OMAFA staff of different ages and genders were asked to rank the appearance of the bunches. The opinions of these staff mimics those of consumers that would be purchasing bundles from a lavender farm.
The forced-air kiln preserved the lavender bundles the fastest, taking two to three days total. This timing would be consistent, regardless of exterior conditions at the time of drying. In the barn rafters and storage room, bundles were dry after six days. Bundles were fully dried by day four in the greenhouse. The bundles in the hoop house took the longest to dry, taking an average of ten days. The barn, storage room, hoop house, and greenhouse options are highly variable, depending significantly on outdoor/indoor temperature, humidity, and weather conditions. At the time of this experiment, environmental conditions were quite warm, with little rain and humidity. Drying times in the greenhouse, barn rafters, and hoop house can therefore be much longer than what we experienced in this experiment.
Colour quality was best in bundles dried in the air-forced kiln, barn rafters, and storage room. When multiple OMAFA employees were asked to identify the bundles they thought looked the best, these three treatments won almost every single time. In these locations, stems are not bleached by sunlight and dry fast, preserving colour the best. The colour of both the buds and stems was slightly faded in bundles dried in the greenhouse, due to the intense sun exposure present in that location. Bundles preserved in the hoop house were the most discolored, with buds displaying browned/burnt tips, and browned stems. The increased drying time allowed these bundles to start decomposing before the preservation was complete.
Figure 1: the Lavandula angustifolia ‘Melissa Lilac’ lavender bundle dried in the kiln (shown on the left) versus the lavender bundle dried in the hoop house (shown on the right).
Figure 2: Lavandula angustifolia ‘Melissa Lilac’ bundles from each drying location.
Figure 3: Lavandula angustifolia ‘Hidcote’ bundles from each drying location
Figure 4: Lavandula x intermedia ‘Gros Bleu’ bundles from each drying location.
Figure 5: Lavandula x intermedia ‘Phenomenal’ bundles from each drying location.
In this experiment, a maximum of sixteen bundles were dried in a single location, except for the air-forced kiln. The number of bundles drying in one location can significantly influence the preservation process. The air-forced kiln would not be impacted by the number of bundles dried in the location because of the electronic air circulation and temperature and humidity control. The barn rafter and greenhouse locations could be impacted by presence of many bundles. Indoor storage rooms and the hoop house locations would be much more affected. The presence of more bundles creates higher humidity as the bundles dry. The number of bundles drying should be a consideration while deciding which preservation method to use.
Overall, we would recommend growers dry bundles either in a forced-air kiln, barn rafters, or indoor location such as a storage room to maximize colour quality in dried bundles. We do caution you that drying in a barn when temperatures are low or during rainy periods can cause browning of buds and stems, similar to what was observed in bundles dried in our hoop house. We also want to draw attention to the cost of forced-air kilns. Although consistent while drying bundles, these machines are expensive. There are other drying methods that are much more economically friendly, such as barn rafters. Understanding stem density, temperature, and humidity balances will allow you to successfully dry bunches, yielding bright, well-preserved bundles.
