Lavender Crop Update – Spring Pruning and Crop Management – May 27, 2022

Lavender flower buds are just becoming visible on undamaged lavender plants. On damaged plants, flowering can be delayed by a week or two and the flowering may be more staggered. This can make harvest timing more difficult.

Growers have been asking what to do about plants that were severely damaged by winter kill. The most damaged plants appear to be those that were not covered with row covers over the winter. Among uncovered plants, lavandins and cultivars like ‘Super Blue’ that were in full bloom in the fall are the most damaged. It is possible that the extremely wet conditions in the fall did not allow plants to harden off sufficiently before going into the winter. Winter conditions were not severe enough to cause this much damage on their own.

By now the extent of the damage and the potential for recovery should be obvious. For angustifolia cultivars with extensive damage, new growth should be coming from the base of the plant if the plant has a hope of recovery (Figure 1). There are some plants that have only very small new shoots (<1 cm) coming from the base. If that new growth does not rapidly expand over the next week, there may not be enough leaves to keep the roots alive and the plant may not recover. Growers can cut back angustifolia cultivars with obvious new growth growing from the base to near the crown so there is plenty of light getting at this new growth. These plants will bloom this year, but at a much smaller size and more uneven than would be expected from a healthy plant. Since the root system is still extensive, the new growth will likely be vigorous, and the plants could get back to a good size by the fall.

Figure 1. New growth emerging from the base of a severely damaged angustifolia plant.

Lavandins behave very differently in response to winter damage. They tend not to send new shoots from the base of the plant in the spring. Cutting these back to the base would most likely kill the plant. Most growers are reporting a ring of live branches around the outside with varying levels of damage in the centre of the plant. The only option with the lavandins is to prune out the dead tissue and leave the live branches intact. If there are enough live branches, new shoots may eventually grow from lower down on those branches. Once the new growth is established, usually by August, the plants can be more aggressively pruned to encourage the new growth and get the plants back to a more rounded shape. If less than 10% of the plant remains alive, the plants may not recover into a rounded shape and may need to be replaced. However, it is best to wait a couple of weeks before making that decision to see how much they recover.

Over the next few weeks, here are some additional considerations for lavender:

Four-Lined Plant Bug

Four-lined plant bug nymphs will begin feeding soon if they haven’t started already. Look for distorted leaves and stems at the very top of the shoots with brown spots on the leaves, as shown in the life cycle diagram in Figure 2 below. You should be able to see a small, bright red nymph in the area, but you must be quick because they duck behind the leaves and hide when you approach the plant. Growers often do not encounter these pests in the first year or two on a site, but they build over time and can cause major damage if not controlled. They are mainly a concern for the appearance of plants in the field and for fresh or dried bundles because the damage is mostly cosmetic and confined to the leaves and stems (not the flowers).

Figure 2. Life cycle of four-lined plant bug on lavender. Young nymphs and the associated damage to lavender are illustrated on the right. © Queen’s Printer for Ontario, Toronto.

There are no controls registered specifically for four-lined plant bug. However, if you are seeing damage to the tips of many of your plants, then it is likely damage will be extensive. An insecticidal soap applied for aphid control may provide some suppression of nymph populations, but only if applied when nymphs are still very young (i.e., within the next week).

Fertilizing Lavender

Now is a good time to apply fertilizer to lavender. It is best to split nitrogen application over the season with some applied now and some applied after harvest in July or early August. Nitrogen can be applied even more frequently at reduced amounts but that is only marginally beneficial (e.g., when heavy rains wash the nitrogen out of the root zone and it has to be replaced). Research has shown that lavender yield is optimized with 80-100 kg/ha of nitrogen total over the season. Potassium and phosphorus rates are best determined by a soil test submitted to an OMAFRA accredited laboratory ( Potassium and phosphorus are best applied before planting so they can be incorporated into the root zone. If applied to an established crop, they only need to be applied once in the spring.

Spittle Bugs

Spittle bugs are showing up in lavender. Look for balls of spittle surrounding a stem (Figure 3). Inside of the spittle is a small, yellowish/green bug that sucks the juices from the stem. Spittlebugs are the nymphs of froghoppers. While they are unsightly and can cause minor damage to the crop, they do not usually cause enough damage to warrant a control.

Figure 3. Balls of spittle showing up on lavender and many other plants in the landscape are due to spittle bugs. The spittle acts as a protective coating that keeps the soft-bodied nymphs moist.

About Sean Westerveld

Ginseng and Medicinal Herbs Specialist, OMAFRA
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