Winterkill

By now, row covers should have been removed in all lavender-growing areas of the province. Remember that row covers are not meant to protect against spring cold; they are meant to protect against extreme winter cold and drying winds. In the spring, they can act like a greenhouse and cause the plants to advance too early, making them more prone to frost damage in May. It is a good idea to keep them handy, as they can be useful to protect flower buds from late-spring frosts. In that case, they would be put back on for one or two cold nights.

The winter was much colder than the previous several winters, so winterkill is a possibility for any plants not protected by either deep snow cover or row covers. With thinner row covers, there may also be damage to the top of plants under the cover. It is too early to determine the extent of the damage because a) sometimes brown stems can sprout new growth after a few weeks of warmth, and b) sometimes stems/leaves that appear green coming out of the winter continue to dry down and die after a few weeks due to damage lower on the stem.

Another type of winterkill is the death of roots due to saturated soils. This can often be confused with cold-temperature damage. The difference is that saturated soils or flooding often kill entire plants, whereas winterkill will often leave some branches near the ground alive. A deep snowpack combined with heavy spring rains could lead to some plant death in areas with a long duration of saturated soils, especially on flat ground.

Aim Herbicide

As outlined in this post, Aim EC Herbicide is now registered for use on lavender as a hooded spray application between rows. Aim is a burndown herbicide, meaning that it will kill the tender foliage of most broadleaf weeds but will not kill the roots. It is a conventional product, so it is not permitted in organic production systems. It will also kill any lavender foliage that it contacts, which is why it needs to be applied with a hooded sprayer beside the rows.

In lavender production systems consisting of strips of plastic mulch with grass between rows, a major issue is the inevitable creep of weeds over the plastic mulch and into the plants over time. These weeds are difficult or impossible to remove once they are established because the plastic prevents any means of mechanical control, and hand weeding can be too costly. These weeds can also contaminate the harvested product as their flowers grow up through the plants. The benefit of a burndown herbicide like Aim is to prevent the creep of broadleaf weeds in the first place by repeatedly burning down the edges of the row. Combined with regular applications of Centurion or Select herbicide for grass control, which can be applied right over the row or next to the row to kill many grasses, this can provide good control of a broad spectrum of weeds in the lavender row.

To be effective, herbicides are best used early/preventatively to kill younger weeds. Once weeds are well-established, the herbicides will not be as effective, and more applications and/or higher rates may be required for control.

If you are unfamiliar with the use of these products on lavender, it is best to try them on a small area first to ensure your equipment is getting the required coverage without causing damage to the lavender plants. For those new to agriculture, you will need a Grower Pesticide Safety Course Certificate to purchase and use most commercial pest control products in Ontario (including organic products). It is best to take a course proactively so that you are prepared if you suddenly need to control a pest mid-season. Courses are offered through the Ontario Pesticide Education Program.

Fertilization

Given the amount of misinformation on the internet about fertilizer and lavender, it is good to remind growers that lavender yields will be improved through proper fertilization. Yields were maximized with 80-100 kg/ha of nitrogen (N) per season in a four-year nitrogen fertigation trial on lavender. While trials on phosphorus (P) and potassium (K) have not been conducted, I have observed significant plant stunting in areas with low soil P and K concentrations. This is especially true for lavender grown on former hay or pastureland that did not have a consistent fertilization program.

For any new lavender plantings, now is a good time to collect soil tests and send them to an accredited laboratory for a basic soil analysis, which will include P and K. Adjust P and K levels in the soil ahead of planting, because these nutrients are harder to deliver to the roots once grass and plastic mulch are in place. To learn how to collect a soil test and interpret the results, click here. For lavender, a good starting point is to use the P and K recommendation tables for lettuce, which can be found in Publication 839 Guide to Vegetable Production in Ontario.

Nitrogen applications should be split into two or three applications per year, with the first one applied at green-up in May.

Click here for information on calculating fertilizer rates in lavender.