The park is best known for its midsummer displays of subalpine flowers, but there are other flora such as at Rhododendron Flats, near the park's western entrance, which has a substantial colony of pinkish-red rhododendrons, a protected indigenous species that blooms in early- to mid-June.
The network of mainly informal gardens displays a multitude of exotic and delicate plants from as far afield as Chile, Madeira and Tasmania, all sheltered by windbreaks of pine trees and ornamental rhododendrons.
The rhododendrons along the "Rhododendron Mile" were a gift to the city from Mrs Russell Sage, in 1909.
The soil and climate in the area is ideal for rhododendrons and there are two rhododendron gardens in the area, including the former garden of the New Zealand Rhododendron Association, which was largely built by John Stuart Yeates, now called Heritage Park.
He then hired English landscape architect Edward Milner who, on the basis of plans completed in 1870, laid out a park for his world collection of rare botanical plants as well as the many rhododendrons which are also a great attraction to tourists.
It was actually in Paris that Mirbeau wrote the first seven letters, centering on Ceylon and Pondicherry, and then in the Orne, near L'Aigle, where, while contemplating the rhododendrons of Normandy, he pictured in the last four letters the twelve-meter high rhododendrons of the Himalayas, glimpsed in an apocryphal trek across Sikkim.
Forests and smaller wooded areas within the park are comprised mainly by cork oaks (Quercus suber), Portuguese oaks (Quercus faginea), Pyrenean oaks (Quercus pyrenaica), olive trees (Olea europaea), alders (Alnus glutinosa and Alnus incana incana), holly trees (Ilex aquifolium), bay laurels (Laurus nobilis), rhododendrons (Rhododendron ponticum), ferns, mosses, and lichens.
Providing shade for the rhododendrons are many mature trees, including more unusual specimens such as Davidia involucrata ('handkerchief tree').
Heathdale - ericaceous and Appalachian Plants, including Catawba and Rosebay rhododendrons (Rhododendron catawbiense and R. maximum), azaleas (Rhododendron spp.), dog-hobble (Leucothoe fontanesiana), mountain laurel (Kalmia latifolia), as well as hemlock (Tsuga canadensis, T. caroliniana, and T. sieboldii), dogwoods (Cornus spp.
Heath plants common to this ecology include mountain-laurel, Kalmia latifolia, various blueberries, genus Vaccinium, huckleberries, genus Gaylussacia, sourwood (or sorrel-tree), Oxydendron arboreum, and azaleas and rhododendrons, genus Rhododendron.
The collection of specimen trees and shrubs include towering American White and English Oaks, lindens, tulip trees, bald cypress, and Chinese Golden Larch, as well as different species and cultivars of azaleas, lilacs, viburnums, hollies, weeping cherries and rhododendrons.