Despite the weather forecast of sunny and 98F, it was time to prune the lavender 'Grosso'. The flowers were just about done, and the secondary growth was already a couple of inches long, so I made my apologies to the bees and got to work. 'Grosso' is an x
intermedia hybrid, which means that it is a cross between the "English" lavender
L. angustifolia, and the spike lavender
L. latifolia. This cross results in plants that have much longer stems than
L. angustifolia which is useful for crafts and bouquets, but it also results in plants that are said to be more productive of oil for perfumery. I don't know if it is true, but it is said that the intermedia hybrids, especially 'Provence' and 'Grosso' are used in the perfume fields of France. I wouldn't be surprised. When pruning the plants, I get sheaves of stems from the intermedias, and just a few bunches from the angustifolias. The stems above are from four plants, minus as many stems I could grasp in one hand to stuff into the hubby's Harley sidebag. My three plants of 'Hidcote' gave me just a handful of short stems.
Another effect of the cross is that the fragrance is more camphorous than the sweetness of straight
L. angustifolia, a very noticeable difference to my nose. Another effect I noticed while pruning the plants today is that the growth is rather different. My 'Grosso' and 'Provence' lavenders grow mostly from the ends of the stems, and the year's new leafy stems can grow quite long before the flower spikes appear at the ends. As the flowers are blooming, secondary growths appear on those stems, and can give a secondary bloom (more so on 'Provence'). Since growth rarely appears at the base, the effect over the years is that the plant keeps getting bigger even though the new growth is shorter as the plants get larger. In young plants, the new growth can add a foot more more into the height and width of the plant within a year. I've read that to keep the plants vigorous, that you should prune the stems hard after flowering, to just above the lowest set of leaves. Even so, my plants get a lot bigger each year. Pruning into leafless wood just kills that branch since new growth doesn't form in old wood.
With
L. angustifolia, plants frequently throw new shoots from the base (I notice this especially on 'Hidcote' but on others as well). Growth in the spring is shorter and the secondary growths are shorter. The plants seem to grow to a certain size, then branches may die back with growth from the base. The overall effect is that mature plants stay about the same size. Cutting back plants hard may kill the plants like with
L. x intermedia, but more often, they produce new shoots and come back.
Something to keep in mind when pruning lavender is that lavender oil is soporific (sleep inducing). So if you prune without wearing gloves like I do, you may find yourself taking a long nap afterwards.
