Lavenders - What Do They Want?
Lavenders originate from the Mediterranean region. This includes the Middle East, Southern Europe, Northern Africa and many of the islands in and around the Mediterranean. Consequently they have adapted to fairly harsh and dry conditions. Many of the soils in these areas, and parts of France and England where much of the early cultivation was done, have a high Calcium content. Calcium is a key secondary nutrient for plant development. The three primary nutrients are Nitrogen (N), Phosphorus (P) and Potassium (K). The other two secondary nutrients are Magnesium (Mg) and Sulphur (S).
Various nutrients have different specialist functions. Plants grow best (in general) when there are ample supplies of both the primary and secondary nutrients. Some cannot grow if there is a deficiency of one or more of them. Other plants cannot grow if there is an imbalance between the nutrients, e.g. Grevilleas and Phosphorus. What this creates is ranges of plants that have adapted to specific soil types, and thus require modification of any soils they are planted into. This is the case with Lavenders that have evolved on soils high in Magnesium and Calcium. Thus they have developed a need for greater amounts of both these nutrients than the average plant.
However, Nitrogen levels in the areas where lavender grows naturally are quite low. Lavenders will grow in these low concentrations, but will take off if given plenty of nitrogenous fertilisers, provided there is ample Calcium and Magnesium. Thus it is recommended that lavenders should be given annual feeds of Calcium and Magnesium. Calcium is best applied in the form of lime which usually contains a small amount of magnesium. However dolomite lime has a higher level of magnesium which gives better results).
We also give regular feeds with high nitrogenous fertilisers. There are several on the market that also have some Calcium included. An annual application of potassium three to four months prior to flowering will improve flower quality.
Lavenders also grow well in very dry conditions and are quite drought tolerant. This does not mean that they don't like water, but require it supplied under well drained conditions. These can be obtained by potting into a very open mix or planting out into raised beds. Regular watering, preferably not on the foliage will also increase growth rate.
The other two requirements of lavenders are good air movement and high light levels. Don't get light levels confused with temperature and day length. They will tolerate quite cold conditions (including snow), provided they have good drainage, plenty of air movement and high light levels. We believe it is the ‘volume of light that makes the most difference. Long cloudy days will not give the same results as medium length days with strong sunlight. These levels can be enhanced by the addition of a reflective mulch, like crushed quartz or other white materials, this will reflect the light back up under the foliage.
Regular feeding, watering and good light will greatly improve growth rates and plant quality.