Lavender bloom is finished except for some cultivars that continuously bloom or have a second bloom. While many growers are focused on essential oil distillation and other postharvest practices, it is important to continue to monitor and maintain the crop. Here are some late-season reminders:
Table of Contents
Pruning
August is the best time to prune lavender in Ontario. This is the time of year that a hard pruning should be done to keep the plants in a dense, rounded shape. For new growers, this practice can seem disheartening, as significant new growth can be cut off. However, the plants will recover quickly and will be far healthier heading into the winter. Pruning should remove about 1/3 to ½ of the green portion of the average stem (not including the flower or portions of the flower stem remaining on the plant). Most of the growing points of the branches should be cut off (not just the leaf tips). This will activate side buds, causing multiple new stems to replace each single dominant stem. The benefits of this include:
- Denser foliage going into the winter, reducing winter kill by reducing air flow through the canopy on cold, windy days.
- More stems, resulting in more flower beds next spring.
- A sturdier plant, which will prevent flowers from falling to the sides under their own weight during bloom.
It is best if pruning can be done before Labour Day. Anything pruned later may not have enough time to resprout before winter, reducing the benefits of pruning and increasing winterkill.
For first-year plants, prune back enough that most of the growing points of the stems are cut off (Figure 1 and 2). This may need to be done two or three times in the first season. Some pruning may be required into September. Many of these young plants will bloom in the first year, sometimes heavily. This makes the pruning very disheartening (Figure 3), but an essential step in ensuring a healthy plant.
Figure 1. ‘Munstead’ plants planted as a 50-cell plug on June 24 and lightly pruned once in July. Top – before pruning on August 28; Bottom – after pruning.
Figure 2. A ‘La Diva Spirit Pink’ half-pruned to show the extent of a good pruning of a first-year plant.
Figure 3. ‘La Diva Eternal Grace’ plants in full bloom (top) and after pruning (bottom).
Figure 2 also shows how much colour some newer cultivars like ‘La Diva Eternal Grace’ can have just two months after establishment as a 4” plant. This full bloom on August 28 shows its potential to provide colour for late-season agritourism activities as a first-year plant. Of course, using the plants for this purpose would delay pruning, which could have other consequences. These newer cultivars have shorter stems, something desired for home gardens, but a less desirable trait for agriculture. They are often less hardy over winter because they never stop trying to bloom.
Fertilization
Nitrogen fertilization is best completed before the end of August. Similar to late pruning, any later applications of nitrogen fertilizer could promote significant vegetative growth in the fall, which could be more prone to winterkill.
Disease
Some areas have experienced heavy rains in August. This could lead to root disease issues that cause wilting or yellowing and death of all or part of a plant. We are conducting a trial this year to diagnose root and stem diseases of lavender, and we need your samples! If you have any symptoms of plant death and would like them diagnosed, please contact me at sean.westerveld@ontario.ca. Diagnosis will be free of charge, except for the cost of shipping the sample to Simcoe if it cannot be delivered in person.
