Bloom is just beginning in the southwest which is several days later than normal (Figure 1 and 2). The winner this year for earliest blooming cultivar in the plot is “Twickel Purple” (Figure 3).
Figure 1. The cultivar demonstration plot at Simcoe (Norfolk County) on June 23. Although full of colour, only a few blooms are actually open on three of the angustifolia cultivars.
Figure 2. “Super Blue” with the very first blooms at Simcoe on June 23. This is slightly early for dried bundle harvest because some buds are not fully developed yet.
Figure 3. “Twickel Purple” with a tuft of flowers in full bloom.
Here are some things to consider during the bloom period:
Table of Contents
Harvest Time
Many growers were on the OLA webinar last week that included a discussion on harvest time. There are basically three main harvest times depending on the end use of the lavender:
- Near the beginning of bloom for dried bundles and buds to avoid too many dried corollas (petals) on the buds.
- At around 1/3 bloom for fresh bundles so many flowers are open but not too many have started to die and turn brown.
- After peak bloom to after bloom for essential oil extraction. Peak yield and quality will be slightly after peak bloom (when >50% of buds have opened or finished blooming), but harvesting at that time would cut agritourism season short. Decent yield and quality can still be achieved after bloom is finished, but the later you wait, the lower the yield and quality will be, especially if buds start falling off the stems.
The uneven bloom shown in Figure 3, which is often the result of winter damage or microclimates within the plant, will make harvest timing decisions more difficult. Consult the following article for a more detailed discussion on harvest timing: Harvest Considerations for Lavender. You can also find a recording of last week’s webinar on the members only page of the OLA website.
Irrigation
Bloom is a critical time for optimal irrigation in lavender because the plants are often double the size compared to the rest of the year and transpire considerably more than normal. This often coincides with some of the hottest weather of the year. As a result, plants could be using at least twice as much water per day as normal. Most areas received decent rains over a week ago, but plants could be getting water stressed again. Showers are in the forecast for the next week, but it is risky to count on forecasted rains to supply the needs of the crop. By the time you find out that the forecast did not pan out, it may be too late to prevent significant yield loss. You may not need to irrigate, but it is very important to monitor your soil moisture regularly and irrigate when needed. If flowers begin to arch over in the heat of the afternoon, you have enough moisture stress that yield potential for either this year or for next year could be affected.
Although it may sound counterintuitive, plants on heavy soils (i.e., clay, loamy clay) may be the most at risk of drought stress. This is because wet conditions over the winter on heavy soils often leads to root dieback. As a result, the plants may come out of the winter with a limited root system. Growers are often afraid to water these plants because they don’t want to cause further root dieback. However, watering these plants is critical because without it the plants may suddenly wilt when severely water-stressed, and they will be unable to develop new roots to replace the root dieback from the winter. Watering a dry soil at this time of year will not cause root dieback. That occurs when soils are saturated for extended periods, which is most common in winter and early spring.
Here are some resources on soil moisture monitoring:
Monitoring Soil Moisture to Improve Irrigation Decisions
Estimating Soil Moisture by Feel and Appearance (Michigan State University)
Fertility
If you have not applied any nitrogen fertilizer so far this year, then now is a good time to make the first application. My research has shown that lavender requires around 80-100 kg/ha of actual nitrogen per year. This is probably best split into two or three applications between late May and early August. If you opted for organic sources of fertilizer (e.g., manure, compost) or slow-release fertilizers, then that nitrogen is available over a longer period and split applications may not be required. With the rapid plant growth during flowering, it is also a good time to look out for any potential nutrient deficiencies (e.g., yellowing of lower leaves, stunted flower development, interveinal yellowing (chlorosis) of leaves etc.). We do not have any resources on nutrient deficiencies in lavender, but here are some guides from other crops that may help:
Diagnosing Nutrient Deficiencies (field crops)
Nutrient Deficiencies for Tomatoes
Soil and/or plant tissue testing can help diagnose nutrient deficiencies, but because we do not have any guides on nutrient sufficiency levels in lavender, it is best to compare areas with poor growth or nutrient deficiency symptoms to a healthy area nearby.
Pests
Four-lined plant bug is usually the biggest pest concern at this time of year. By now the nymphs have been feeding for about a month and the adults have emerged. You may see extensive damage to the newest leaves (i.e., brown spots, curled leaves) and stems (i.e., blocking yellowish/brown patches between the canopy and the flower heads). It is too late to do anything about this insect for the year. They will stop feeding soon and lay eggs for next year. Where you see the damage this year, you will likely have the problem again next year and it could be even worse. The only time of year that you can even attempt to manage this pest is in late May when the youngest nymphs emerge.
Keep an eye out for garden fleahopper as well. These tiny black (adults) or green (nymphs) insects will inhabit the inner canopy, sucking juices out of the leaves. They can reach levels so high that the plants can become defoliated by August. For more information on garden fleahoppers consult the following blog post from last year:
