Re: re. speaking of lavenders

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David,

It is not surprising that you are a bit confused about the name of Lavandula multifida.  This species has been in the nursery trade in California for over 30 years, but more often than not, under different names.  For several years San Marcos Growers offered it as L. pinnata var. buchii--a conflation of two distinct species!  This situation was improved when I rewrote the entry Lavandula for the 2000 edition of the Sunset Western Garden Book.  Publication in 2004 of Tim Upson and Susyn Andrews' monumental monograph, The Genus Lavandula, (Timber Press, ISBN 1 84246 0106), with its superb colored botanical illustrations of 39 species of lavenders, left no doubt whatever to the identities of the various species offered in the trade.

L. multifida, native to southern Spain and Portugal, Morocco, and coastal Algeria, is the hardiest of the fern-leafed lavenders.  In my experience, it manages to survive down to about 25 degrees F.  I use it in many of the gardens I care for because for us, it is seldom really out of bloom.  I hate to cut off the fresh blooms, so whenever it is feasible, I teach my helpers to cut back individual spent flower stalks to new side growths and remove any dying branches right back to green wood.  If the plants get too rangy, I usually cut back individual branches rather than shearing the whole plant--again too tender-hearted to sacrifice all the bloom when it is making an otherwise good show.  But where labor is at a premium or cleanup has been delayed, I shear the entire plant into a compact, rounded mound, then cut out individual dying branches if necessary--a couple of times a year. .  I try not to remove more than 1/3 of green growth if done in hot weather, but in early fall (usually October for us) or in spring before May they will come back from removal of 2/3 of green wood.  For me, they usually die if I cut them back to just sticks without new foliage. 

The other species in this group--L. canariensis, its hybrid L. x cristiana, L. pinnata, L. buchii, L. pubescens, and L. minutolii and their various subspecies and varieties all turn up their toes if the temperature goes below 35 degrees.  But they are very handsome plants with very long blooming seasons.  And most will come back from seed when the weather warms up if the soil is not mulched or covered by competing plants.  Many of these species in the subgenus Fabricia, section pterostoechas, are interfertile, and some interesting and horticulturally valuable hybrids may show up.  For mediterranean climate areas, I think they are well worth growing as very drought-tolerant, reseeding annuals for full sun.

I am surprised that David did not mention that he grows the toothed or "French" lavender--especially L. dentata var. candicans.  That also blooms year-round for us, and the blue-violet blossoms and bracts show up very well against the silvery-gray foliage.  It is much hardier than L. multifida (winter before last it went through five straight nights below 21 degrees--two down to 16 F. without any problem).   Again, I try to keep it in bloom by removing spent flower stalks and any dead branches.  When it does open up in the center, I find it usually sprouts new shoots that eventually fill in the gaps and restore its fullness.  On the other hand, it will endure almost any degree of shearing in cooler weather without flinching.   If done in winter or early spring, it can be cut back to two inches from the ground and will resprout as a compact, very dense mound of new shoots the way a pruned santolina will.  Just don't cut it back hard when the weather is very hot and the sun intense or you may lose it (a good rule of thumb for almost any mediterranean plant).

I find that the hybrids of L. dentata--L. x heterophylla, L. x allardii, L ginginsii, and 'Goodwin Creek Grey'--are more rangy and less colorful than the species.  They are more suitable to an informal, more-or-less wild setting, with other mediterranean shrubs and drought-tolerant perennials and sub-shrubs.  I find they quickly outgrow a small garden with regular irrigation, their flowers are not particularly colorful, and their fragrance is rather medicinal.  If I had room for them, I would rather grow any one of several cultivars of L. x intermedia instead.  (I know some partizan of one or another of them will quickly jump to their defense.  To each his own)  ;-)