Robinia pseudoacacia Umbraculifera - Parasol Acacia

Robinia pseudoacacia 'Umbraculifera' is a small tree with a straight trunk topped by a ball of foliage. Widely planted by urban landscapers in the 1960s-1970s, it is grafted as a half-standard and naturally develops a globular and dense crown. Its foliage appears late in spring, and it is one of the last trees to lose its leaves in autumn. This non-flowering variety is cultivated for its regular and classic architecture, which structures small well-kept gardens and works wonders in parks. This locust tree owes its success to its great ease of cultivation in any soil and under almost all our climates, except in excessively windy regions.

'Umbraculifera' is an Austrian horticultural creation dating back to 1811, derived from Robinia pseudoacacia, native to the Eastern U.S.A. It belongs to the Fabaceae family, which are capable of assimilating atmospheric nitrogen at their roots, so they do not need soil rich in organic matter to develop. 'Umbraculifera', with a smaller spread than the species, naturally displays a spherical, dense, and regular habit, conducive to bird nesting. If not grafted on a stem, it will form a ball at ground level. This variety is most commonly sold grafted on top of Robinia pseudoacacia. It is a medium-longevity tree with relatively slow growth. It typically reaches an average height of 5 m (16.4 ft), with its very dense crown spreading over approximately 4 m (13.1 ft), slightly less if pruned. The bark is initially smooth, before taking on an interesting grey-brown colour and a somewhat fissured texture with age. The well-dense branching is composed of slender, relatively brittle branches, reddish-brown in colour, and non-thorny. Its deciduous leaves, 15 cm (5.9 in) long, are divided into 9 to 21 ovoid leaflets, slightly smaller than those of the species. They are decorative, transitioning from dark green in spring and summer to yellow in autumn. Note that this locust tree does not age well after severe and repeated pruning.

This 'Umbraculifera' locust tree is suitable for both small and large gardens, but it is not recommended for situations exposed to strong winds. It is ideally planted as a standalone tree in a small urban garden, in the centre of a well-kept bed composed, for example, of ground-cover roses, boxwood, creeping Japanese spindles, or Lonicera nitida. It does not hinder the growth of other plants, as its shadow is not significant. However, its relatively shallow root system draws water in summer. Consequently, it is preferable to choose plants that are not water-demanding or to plant outside the perimeter delimited by its crown.

Note: The root system of the rootstock (Robinia pseudoacacia) tends to sucker easily, following severe pruning or injuries to the roots. The suckers are thorny, just like the rootstock tree.