Rhododendron serpyllifolium - Thyme-leaved Azalea

Rhododendron or Azalea serpyllifolium is a rare botanical Azalea native to Japan, very interesting from an ornamental perspective. It is probably the species that bears the smallest leaves, resembling those of Wild Thyme (Thymus serpyllum), hence its species name, literally "with thyme-like leaves". In spring, it produces an abundance of charming small flowers in a lilac pink. This dwarf bush thrives in partial shade, in moist, humus-bearing soil with a tendency towards acidity, and appreciates mildness and atmospheric humidity. It will be perfect in a small Japanese garden or a natural-looking garden.

The Azalea, which in botanical terms is actually a Rhododendron, belongs to the family Ericaceae, which houses many favourite genera for garden lovers, such as Leucothoe, Kalmia, Heathers, and even some plants with edible fruits (blueberry, strawberry tree, bilberry...). The Rhododendron genus comprises over 1000 species, ranging from dwarf shrubs 10 or 20 cm high to small trees 10 to 15 m tall, from cold and temperate regions to the tropics. This group of plants is so vast that it is subject to a rather complex botanical classification. Rhododendron serpyllifolium belongs to the section Tsutsusi, whose members are characterised by producing larger spring leaves that are deciduous, and smaller summer leaves that persist until the end of winter, and sometimes even visually uniform and evergreen leaves.
Azalea serphyllifolium is endemic to Japan, where it grows naturally in the southern half of Honshu Island (the large central island of the archipelago that houses Tokyo), as well as on the two southern islands, Shikoku and Kyushu. The species was introduced to England by Charles Marie in 1880, where it first bloomed in 1882. Semi-evergreen depending on the climate, this rather slow-growing Azalea forms a compact shrub 50 cm in all directions within 10 years of planting. At maturity, it will reach a maximum height of 0.80 m, or up to 1 m, if it enjoys its location. It is quite hardy (-15°C to -20°C), but it prefers mild and even warm climates, and especially humid conditions. The species is remarkable for the small size of its leaves: slightly obovate and narrow, only 5 to 20 mm long and 3 to 6 mm wide. Growing alternately on the branches, they are medium green to dark green with small hairs along the edges. The dark brown stems themselves are covered with small hairs, laid against the stem and directed towards the tip of the shoot.
In April-May, the shrub produces a beautiful, particularly abundant and graceful flowering. Small flowers, most often solitary or grouped in pairs, bloom at the ends of short branches. They consist of a funnel-shaped corolla, spreading at the top and tubular at the base. The five well-opened petals reveal five long stamens that contribute to the grace of the flower. The flowering is generally lilac pink, but there are forms with white flowers, which have been described and classified as a subspecies.

Rhododendron serpyllifolium, with its romantic charm, is a very original botanical species that will fit perfectly into a Japanese-style garden. It will pair beautifully with a Japanese Maple such as Acer palmatum 'Orange Dream', whose palmate leaf patterns will not overshadow its tiny thyme-like leaves, while their changing colours in shades of yellow, orange, and light green will create a pleasant contrast. Magnolia stellata with its immaculate star-shaped flowers will also be a good companion. Also consider perennials, such as Hostas whose large decorative leaves will make your small Azalea's leaves appear even finer by comparison.