Most angustifolia cultivars of lavender have begun to bloom this week in the south. Full bloom will likely occur within the next week to 10 days. Early bloom is the time to harvest for bundles and buds. Ideally, most of the buds should be unopened when harvesting for bundles and buds. If harvested too late, the corollas (petals) will dry up and turn brown. These can stick to the calyx (buds) and make them much harder to clean. However, doing it too early could mean the calyxes are underdeveloped, lowering the yield and the quality. It is best to wait until about one to two blooms are open or ready to open per flower stalk. This would equate to less than 10% bloom. Some cultivars have more staggered bloom than others, making the decision of when to harvest much more challenging. Younger plants and those with winter injury also tend to have a more staggered bloom.
For those with frost damage from the end of May, bloom will likely be staggered with undamaged buds blooming soon and damaged shoots sending up new buds a few weeks later. This will make the timing of harvest much more difficult. Selective harvest should be done when the first flush is just starting to bloom. The remainder can be left for oil harvest or subsequent selective harvests. There is a lot more flexibility in harvesting for essential oil, since the yield of oil peaks at peak bloom and only slowly declines after bloom is finished. If harvesting for oil, you can wait until most stems are at or past bloom to harvest.
Are you wondering what caused those brown and yellow patches along your stems? It was probably the four-lined plant bug. Feeding on the leaves results in brown circular lesions but feeding on the stems turns into extended patches as the stem elongates after feeding (Figure 1). The insects are almost done feeding for the year. They will soon lay eggs in slits along the side of the stem (Figure 2). The eggs will not hatch until next May. If you have extensive damage this year, then the time to attempt to correct the problem is soon after egg hatch in mid-May of next year.
Figure 1. Yellow and brown patches along stems due to earlier feeding by the four-lined plant bug.
Figure 2. A tiny line of white eggs inserted into the side of a lavender stem.
Although we all know that bees love lavender, we rarely stop to appreciate the diversity of pollinators that lavender supports. Since we rarely care about the seeds produced by the lavender, the lavender crop does not need pollination. Some growers have honeybee colonies for honey production, but other than that, the bees just tend to be a potential liability as customers walk through the fields and could get stung.
With threats to pollinator health due to a combination of factors including climate change, varroa mites and pesticides, pollinators need all the help they can get. This includes both honeybees and a diversity of native pollinators. The question is, how much of a resource is lavender for pollinators? Last year a team of OMAFRA specialists and summer students tried to answer that question. Pollinators were tracked in apples, raspberries and lavender at different times of day. For lavender, assessments were done from mid-morning through to midnight. Night assessment were done with red-light flashlights so insects would not be attracted to the lights. Specimens were collected for later identification.
So, what did we find? First, honeybees are especially attracted to lavender. That should come as no surprise. During the day, at least 90% of the pollinator activity was from honeybees. It is likely that this would depend on the site. Sites closer to wild areas may have a greater diversity of native pollinators instead. Lavandins appear to be more attractive to honeybees than angustifolias (Figure 3), and purple cultivars appear to be more attractive than white ones. At peak activity, an estimated 2 to 5 bees were on each lavandin plant at any one time. This would equate to around 20,000 to 50,000 bees in one hectare of field. That is equivalent to an entire colony of honeybees in the field at any one time. Considering that the bees must get back to the colony frequently to deposit their load, one hectare of lavender can probably support several colonies of honeybees for the 6 to 8-week bloom period. Since lavender blooms later than most crops requiring pollination, this support comes at a time they are not needed in fruit or fruiting vegetable crops.
Figure 3. Honeybees seem to prefer lavandins over angustifolias.
Second, lavender supports a great diversity of native pollinators including bumblebees, solitary bees, hoverflies, and butterflies (Figure 4). Greater diversity occurs closer to wild areas. In plants in my garden which is close to a wooded area, for example, few if any honeybees were present, but they were visited regularly by several other bee species and hover flies.
Figure 4. Lavender supports a diversity of pollinators other than honeybees including bumblebees and solitary bees, hoverflies, butterflies and moths.
Third, after the honeybees shut down in the evening, an equally great number of moths begin pollinating at dusk and after dark. Although the moth species have not been identified yet, there were several species in the field. The activity in the field after dark was as great as it was with honeybees during the day. These forgotten pollinators may contribute greatly to pollination of native species and potentially other crops. So, take some time this bloom season to appreciate the number and diversity of pollinators that visit your lavender. I am sure creative lavender growers could find many ways to use this educational opportunity as part of agritourism activities as well. I am hoping to incorporate this information in an educational poster later this year.