Certain garden plants are grown more for the aromatic quality of their foliage than for the beauty of their flowers. Their flowers may be insignificant, their leaves may not be particularly handsome, yet the plants are beloved of gardeners because of the scents given off by their leaves, sometimes in hot sunshine, sometimes when the leaves are brushed with the hand, or crushed between the fingers. The latter kind were described long ago as being 'fast of their scent', meaning that the scent was released only by touching the leaves. Such a plant is the well-known lemon-scented verbena (Lippia citriodora, once known as Aloysia citriodora). This is usually grown as a greenhouse plant although it is nearly hardy and will succeed outdoors in most winters in the milder parts of the country, given some protection. It should be planted by a warm, sunny wall, preferably by the doorway or near a path so that the leaves can be pressed in passing to yield their piercingly sharp scent of lemons. Spikes of lilac flowers are produced in late summer.
The white, many stamened flowers of the myrtle (Myrtus communis) are by contrast much more showy and it would be worth growing this shrub for its flowers alone. But to beauty of flower it adds fragrance of leaf. Again, it needs a warm sheltered wall or a pot in the cold greenhouse or conservatory. The old-fashioned lad's love (Artemisia abrotanum), also familiarly known as southernwood, rarely flowers ; it is a hardy shrub grown for the interest and aroma of its finely divided grey-green leaves, so fine as to be almost like hairs. This is another plant which needs to be touched or squeezed to catch the scent which is of lemon, but oilier and not so sharp as that of the lemon-scented verbena. The evergreen leaves of the sweet bay or poet's laurel, Laurus nobilis also release their scent when handled.
Rub the shiny evergreen leaves of the Mexican orange (Choisya ternata) between your fingers and you can smell varnish; those of Hebe cupressoides smell of pencil shavings. The smell of wintergreen is released when the leaves of the Gaultheria procumbens are handled and the smell of eucalyptus oil is given off by the leaves of the blue gum (Eucalyptus globulus) often grown in the conservatory.
The smell of garlic is not liked by everyone; anyone who dislikes it should be careful when planting the bulbs of the spring starflower (Ipheion uniflorum), for if these are by a pathway their lax leaves may be trodden on, when the air will be filled with this unmistakable aroma.
The scented-leaf pelargoniums (`geranuims') constitute a class by themselves. The ordinary bedding pelargoniums have a powerful aroma when handled, which most people find pleasant enough, strong though it is. But there are twenty or more kinds which are grown mainly for their leaf-scents rather than for their far from showy flowers. The catalogs
of specialist nurserymen will list perlagoniums with leaves smelling of roses, lemons, oranges, citronella, eucalyptus, peppermint, pine, and other scarcely definable scents or aromas, released when the leaves are pressed.
It is difficult, too, to define the seen given off by the slightly sticky leaves of Dimorphotheca barberiae, not only when pressed but also on a hot, still summer's day, when the sun's heat releases it.
A few aromatic plants are worth planting between the cracks in paving for they will bear being trodden upon. One of the mints, Mentha requienii, scarcely 1.5cm (1/2 in) high, is one such plant. Trodden upon, it smells distinctly of peppermint. Another useful plant for similar positions is the wild thyme and its varieties. Its relative, Thymus herba-barona, smells of carraway seed, a scent disliked by many because of its associations with seed cake, but not too unpleasant in the open air. This is a shrubby little plant about 16cm (bin) tall which would be damaged by being trodden upon; it is a good dry wall plant. Other thymes, quite apart from the culinary thyme, have leaves with varied scents including orange, lemon and camphor. The leaves of the Carolina allspice (Calycanthus floridus) also smell strongly of camphor when handled.
The mints have a surprisingly wide range of scents, too, for there are varieties which when handled give off such scents as Eau de Cologne, apple, pineapple and ginger. By contrast the leaves of Caryopteris mastacanthus, a low-growing shrub with lavender blue flowers, smell of mint when bruised.
Another good garden plant, especially for edging a pathway where it is easily touched in passing, is the catmint (Nepeta faassenii), grown mainly for its long display of spikes of lavender-blue flowers, but its season of charm is even longer than its flowering period for its grey-green leaves are always aromatic. Lavenders, too, are aromatic in all their parts, flowers, stems and leaves and these make fine internal hedges. So, too, does the old-fashioned rosemary (Rosmarinus officinalis), taller than the lavenders, free-flowering in spring but a delightful plant to have at any time, for the sake of its sharply fragrant leaves. Another of these old plants is the rue or herb of grace (Ruta graveolens) usually grown in the form 'Jackman's Blue', for its blue-green foliage, although not everyone likes that somewhat odd aroma its leaves give off when handled. This is a dwarf shrub which does well on chalky soils. Yet another shrub which comes into the aromatic group is the skimmia, a beautiful evergreen for shade, bearing in most of its garden forms ample crops of persistent bright red berries. A curiously aromatic shrub is the sweet brier or eglantine (Rosa eglanteria) sometimes used to make a low informal hedge. The aroma of its leaves is most apparent on a warm day, after a shower of rain.
Many conifers have a distinctive aroma, often resinous or like that of turpentine. It is usually more noticeable on hot, calm days, though even dead pine needles or the leaves of other conifers smell pleasantly as one walks over them on a winter's day.