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The genus Lavandula is divided into six sections; Lavandula, Stoechas,
Dentata, Pterostoechas, Subnuda and Chaetostachys. Of these the gardener
is only likely to come into contact with the first four.
Section Lavandula
This section comprises three species and an important group of hybrids. The
species are L. latifolia, L. angustifolia (with two subspecies) and L. lanata.
The subspecies are L. angustifolia ssp angustifolia and L. angustifolia
ssp pyrenaica. (For all practical purposes L. angustifolia ssp pyrenaica
can be disregarded, and all further reference to L. angustifolia ssp
angustifolia has, for the sake of brevity, been shortened to L. angustifolia.)
The hybrid group is L. x intermedia (see below).
L. latifolia (sometimes referred to as a ‘spike lavender’) is a rangy,
untidy lavender with axial shoots, long stalks and a conical flower head
which produces large quantities of very camphoraceous oil. There are no
known cultivars of L. latifolia.
In England it does not over-winter readily and is more of curiosity value
than anything else, principally because it is a progenitor of L. x intermedia.
It is mainly grown in Spain, and from it is obtained spike lavender oil.
This is sometimes available in pharmacies but its main use is as a cheap
oil for use in room sprays and the like. It can also add a special
lustre to the varnish used on oil paintings and has been used as a moth
repellent.
L. latifolia is present in our national collection.
L. angustifolia tends to be much smaller than L. latifolia, with short
stalks (9-12 inches/21-30 cm) and a regular flower head which looks rather
like a bottle brush. There are no axial flower shoots. The flower colour
varies from white through to very deep purple. The dwarf lavenders are all
cultivars of L. angustifolia. Unless weakened by damp or damage,
L. angustifolia is not susceptible to shab.
L. angustifolia is the variety used to distil pure, essential lavender oil,
as opposed to Lavandin (see below under L. x intermedia). The oil is used in
aromatherapy and perfumery, both in lavender fragrances and as a part of
fragrance compounds, where it is particularly useful as a ‘lifter’, its high
volatility helping to emphasise the top notes of other less volatile oils.
It is cultivated commercially by us in England as well as in France, Tasmania,
China, Rumania, Bulgaria and Russia, among others.
Depending principally on the cultivar chosen, but also on the place of
cultivation and weather conditions at harvest time, the hundred-plus chemical
constituents of the oil and the habit of the plant will vary.
For the gardener, the following points are important to note:
- L. angustifolia is hardy in the UK providing soil conditions are right.
- It needs a sunny aspect on light, well-drained soil.
- It makes excellent fragrant hedging, attractive to butterflies and bees.
- Be very careful to buy your lavenders from a reputable source. Often,
lavenders are grown from seed and because lavender hybridises so easily,
the seed does not come true and you may not get what you are hoping for.
L. lanata, common name ‘woolly lavender’, is an attractive plant if you
can keep it alive. It has silvery, woolly (or felt-like) leaves which mark it
out as a particularly tomentose (drought loving) plant. Its flower spikes are
pale blue drying down to grey. For the gardener it is the foliage which is
most valuable.
L. lanata has hybridised with L. angustifolia to give L. ‘Sawyers’ and
L. ‘Richard Grey’ of UK origin and L. ‘Silver Frost’ and L. ‘Lisa Marie’
of US origin. It has also hybridised with L. dentata to give L.
‘Goodwin Creek’.
L. x intermedia, also known as ‘lavandin’, a French elision of Lavande
intermedia, is now recognised a group within section Lavandula. The plants
were named ‘intermedia’ because they are ‘between’ L. latifolia and
L. angustifolia but with certain L. latifolia characteristics being dominant:
- They are large plants
- They are prolific oil producers
- Their oil is much more camphoraceous than that of L. angustifolia (but less so than L. latifolia)
- They have axial shoots
- Their flower heads tend to the conical
- They have broader leaves
In addition they are normally infertile and can only be propagated vegetively.
With the exception of ‘Grosso’ they are susceptible to shab.
By far the largest proportion of the lavender grown in France and for
the perfumery industry is lavandin and, because of its disease resistance,
almost exclusively ‘Grosso’. For the gardener, those lavender plants often
seen in cottage gardens are L. x intermedia plants – large, woody and,
like many a spaniel, enthusiastic and somewhat out of control.
There is a theory that when pruning plants from this subsection you should
not cut into the old wood. That theory has not always been borne out by our
experience here at Caley Mill.
Section Stoechas
The distinguishing characteristic of this section is the flower head topped by
infertile bracts of varying length. The plants hybridise readily, however,
and consequently there has recently been a huge explosion of varieties within
this group, many from Australasia.
This group includes L. stoechas ssp stoechas, L. stoechas ssp pedunculata,
L. ‘Helmsdale’, L. ‘Marshwood’, and L. ‘Willow Vale’. ‘Papillon’ and
‘Butterfly’ are two common names which have been given to L. stoechas ssp
pedunculata by nurserymen to help their sales of that cultivar. Plants
in this group are not used in the production of essential oils because of
their high ketone content.
For the gardener, the plants within this group are largely hardy,
although I am least confident about L. viridis. Cultivational
information is much the same as for section Lavandula. Because of
the risk of hybridisation, make sure that your plants have been raised
vegetively. Dead-headed, Stoechas plants will repeat flower freely.
Section Dentata
Originating from the Mediterranean, this comprises L. dentata and the
silver-leafed L. dentata var ‘Candicans’. It is only used in gardens
and is distinguished by the toothed leaf (hence the name). The flower
head has bracts like L. Stoechas, although not nearly so pronounced.
The dentatas are of doubtful hardiness and are therefore best kept
in pots but given plenty of ‘fresh air and exercise’ in the summer.
L. dentata has hybridised with L. latifolia (from section Lavandula)
to produce the vigorous and beautiful L. x allardii which we have
over-wintered outside here in Norfolk, but keep a spare plant in the
conservatory just in case.
L. ‘Goodwin Creek’, a hybrid with L. lanata, is referred to above.
Section Subnuda
This section, comprising eight species, includes lavenders from
Arabia, Socotra and Somalia, of which the most important are
L. Subnuda, L. macra and L. aristibracteata.
Section Chaetostachys
This group comprises two species from central and southern India –
L. bipinnata and L. gibsonii.
The cultivars of L. angustifolia, L. lanata, L. x intermedia, L. stoechas,
L. dentata and L. pterostoechas which we offer are described and illustrated
in our plant catalogue each spring and autumn and are on sale at the
Conservatory. The varieties in the National Collection are listed on
our website.
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