There are 47 species of Lavandula, but the four that many gardeners would be familiar with are L.angustifolia, L.dentata, L.pedunculata and L.stoechas. All four are native to various countries within the Mediterranean region, which includes Croatia, France, Greece, Italy, Lebanon, Morocco, Spain and Turkey.
Also worth a mention is Lavandula x intermedia (Lavandin), which is a naturally occurring sterile hybrid of L. latifolia and L. angustifolia. This plant yields much greater volumes of oil than L. angustifolia, but is higher in the camphoraceus components. Lavender oil is produced mainly from the aromatic and edible lavender, L. angustifolia.
When it comes to common names, the terms are imprecisely applied and what one person knows as ‘French’ lavender, another swears black and blue is ‘Spanish’ lavender! L.dentata is referred to as ‘French’ and ‘Spanish’ lavender, L.stoechas is referred to as ‘French’, ‘Spanish’, ‘Italian’ and‘topped’ lavender while L.pedunculata is referred to as French Lavender. L.angustifolia, however, is always referred to as English Lavender and is considered the ‘true’ lavender. Confused, much?!
If you’re looking at it from the perspective of where the plant originates, then the common names for L.dentata and L.stoechas are all correct as both come from all over the Mediterranean; while the common names for L.angustifolia and L.pedunculata are incorrect as L.angustifolia comes from Spain, France, Italy and Croatia (not England!), while L.pedunculata comes from Morocco and Turkey! The discrepancies make sense when you realise that for centuries lavenders have been cultivated in, and become associated with, different countries to where they originated.
Being able to identify the different varieties and getting to know their qualities makes the process of choosing plants for the garden easier. From a hardiness perspective there are four types: (including L. angustifolia and L. x intermedia), which are hardy in most climates, but require a cold period to flower well, so aren’t as reliable in the tropics and subtropics. cope with all but extremely cold winters, so do well in most Australian gardens. Species include L. stoechas, L. pedunculata and L. latifolia. tolerate some frost and include L. lanata, L. viridis, L. dentate and L. x heterophylla. , such as L.canariensis and L. rotundifolia suffer when the temperature drops to freezing, and will succumb if bitten by Jack Frost!
An ‘easy’ way to identify different lavenders is to remember that L.dentata varieties have serrated leaves and L.stoechas and L.pedunculata varieties have brightly coloured bracts or wings at the top of each flower.
Above all else, the three essential prerequisites for growing lavender successfully are full sun (seven hours +), free-draining soil and good pruning.
To increase the amount of light, apply a mulch such as crushed quartz that will reflect light back into the foliage.
Lavenders can be grown all over Australia, including coastal locations, except the tropics. They need hot, dry summers and dry winters. Often it is wet soil in winter that kills lavenders rather than frost. They’re best planted in a north-facing area.
When established, many lavender varieties tolerate frost and snow. In cold climates, positioning lavender close to brick, stone or concrete buildings or fences affords some protection.
Other than L. x intermedia that can grow quite large, lavenders grow well in containers. Use unsealed terracotta pots because they dry quickly. Raise pots off the ground to ensure excellent drainage and, most importantly, only water when they’re dry. It’s better to increase container size as the plant grows, rather than planting a small plant into a large pot. Plant only one plant per pot.
Lavenders make excellent hedges and look gorgeous in rockeries and in pots in courtyards and on verandahs. They work well with other Mediterranean plants such as rosemary and sage, or as part of a mixed herbaceous bed.
Lavender requires a neutral to alkaline pH, but L. x intermedia will grow in slightly acidic soil. For soils with a pH of under 5 add lime, for those above 5 add gypsum.
Plant lavender in well-drained soil or mounds.
For clay soils dig through gravel and/or organic matter such as compost or well-rotted animal manure. For sandy soils, dig through organic matter to a depth of 20-30cm.
Lavenders are pruned for two reasons: To promote healthy growth and produce plants that can cope with pests, diseases and adverse weather; and to create a well-shaped, compact plant.
Tip pruning when young creates a dense, nicely shaped shrub. To ensure the plant’s energy goes into growth alone, remove its flowers until the plant is 10cm high.
For Hardy and Frost-hardy lavenders prune two-thirds of the plant when the flowers lose their colour. Spring pruning is acceptable if you missed the autumn prune; in this case, prune back to small shoots on the stem. L x. Intermedia cultivars bloom later and only the flower stalks should be removed after flowering and the hard pruning carried out in spring.
Half-hardy lavenders should be pruned hard after the flowers first appear in spring, taking them back to small shoots on the stem. Deadhead for the remainder of the flowering period.
Tender lavenders mostly require dead-heading only through the year, with an occasional hard prune to keep their shape;
Lavender responds well to pruning and is very popular with topiary enthusiasts.
Lavenders don’t require much fertiliser, but as they evolved on soils with high levels of calcium and magnesium developed the need for greater amounts of these nutrients than most plants. Sprinkle dolomite around the plant after pruning to encourage flowering, and use a high nitrogen fertiliser after flowering.
Apply Seasol and Powerfeed regularly to keep plants healthy and performing at their best.