The warm weather over the past week should lead to rapid green-up of lavender plants. Plants without any winter kill should be obviously green with new shoots beginning to expand at the tips. For other plants, recovery from winter kill has been slow, mainly due to colder than normal weather in April and the first week of May. There have been many concerns raised by growers about uncovered angustifolia cultivars that appear to be severely damaged or even killed. ‘Super Blue’ appears to be particularly damaged. A couple of weeks ago I suggested these will likely come back from the base and along the stems if the stems are still green inside. While I expected a more rapid recovery and shoots emerging all along the green stems, it still appears that plants will come back at the base, even if recovery along the stems is not as expected.
In my previous post I showed photos of three different types of damage. One plant had no obvious green growth and upper stems appeared to be dead, but lower stems still had some green below the bark. After suggesting that this would grow back from the base, I was worried that maybe it wouldn’t, since no new growth was visible. It is just over the past couple of days that a flush of new shoots is beginning to emerge from the base of the plant (Figure 1). If this is the type of recovery you are seeing, it is best to cut the plant way back to within about 5 cm of the base, or just above where green shoots are emerging. In areas further north, you may need to wait a couple more days before deciding how far back to prune. Pruning must occur before flower buds start to be visible in a couple of weeks or you risk cutting off the blooms for the year.
Figure 1. New shoots emerging from the base of a severely damaged L. angustifolia lavender plant.
The second plant had some green tips but most of last year’s growth was dead. As expected, this plant is sending up new shoots from the base, along the stems and near the healthy tips (Figure 2). This plant will likely fill in within the next few weeks, but bloom will be lower than expected. Doing a hard pruning may help focus the plant’s recovery on the new shoots at the base and could result in a more compact plant by the end of the year. However, pruning is not essential for this type of damage.
Figure 2. New shoots emerging from the base and branches of a moderately damaged L. angustifolia plant.
The third plant was a ‘Super Blue’ plant that appeared to be completely dead, except for some green below the bark. Other than one small branch showing some green at the tips within the past week, the rest of the plant looked almost completely dead as of yesterday (Figure 3). Just this morning, however, a tiny green shoot is emerging at the base (Figure 4), along with a bit of new growth along another branch that appeared to be dead earlier this week. This suggests that more shoots will soon emerge from the base. This plant will definitely need to be pruned back hard to get it back into a rounded shape and encourage the new growth at the base of the plant. Plants that are pruned back hard will likely still bloom this year, but the reduced size of the plant will likely result in less than 50% of the expected bloom. Blooms may also be staggered over a longer period rather than all at once, which can make harvesting plants more difficult.
Figure 3. Other than one small branch finally showing some green growth in the last few days (bottom left), this ‘Super Blue’ plant looked completely dead as of May 12.
Figure 4. A tiny new shoot emerging at the base of the ‘Super Blue’ plant in Figure 3 that just became visible on May 13.
If a hard pruning is necessary, the least damaging method to prune the plants is to use pruning shears to cut all the main branches just above the green (Figures 5 and 6). In Figure 6, some shoots were visible about 10 cm up the stem, so they were retained after pruning. If shoots are only at the very base, stems can be cut back further. A hedge trimmer may also be effective if it can get through the woody stems. Other methods like using a rotary mower will cause too much shredding of stems and will miss any stems growing laterally along the ground.
Figure 5. A L. angustifolia plant with winter damage as shown in Figure 1 before pruning.
Figure 6. The plant in Figure 5 pruned back leaving any green shoots emerging from the stem. In this case, more shoots will likely develop over the next few days.
If by early next week no green shoots are emerging, plants are likely dead and will need to be replaced. This should be relatively rare for angustifolia cultivars but is more likely for lavandins that were not covered over the winter. Experience has shown that lavandins (L. x intermedia) are not hardy in Ontario and require row covers to get through normal winters. In severe winters they may be severely damaged even through a winter cover.