Trials of perennial Lavatera indicate that most of these flamboyant shrubs are hybrids between two European species, explains Diana Miller

Above: Lavatera 'Candy Floss' - a compact plant better suited to the smaller garden

One of the most spectacular flowering plants of summer is Lavatera, the tree mallow. The common name is a little deceptive as this genus contains about 25 species, including annuals and herbaceous perennials as well as woody species. The majority come from Mediterranean areas and have large, showy flowers in shades of pink, mauve and white from early summer until autumn.

Following the formation of the Woody Plant Trials Committee, shrubby Lavatera was one of the first plant groups to be selected for trial, partly because it would establish quickly. Planted in spring 1994, the trial could be judged for the first time within a year or so. This enabled the Committee to avoid waiting many years for plants to be assembled, propagated, planted and reach maturity as is the case with slower-growing plants such as Rhododendron yakushimanum hybrids, a trial scheduled to last for at least 10 years.

During recent years tree mallows have gained in popularity and many new cultivars have become available. It was considered a good time to compare these and assess which could be recommended for the Award of Garden Merit (AGM).

A further aim of the trial was to try to ascertain relationships between these plants and the two species suspected of being the parents of most of the plants found in gardens, L. olbia and L. thuringiaca. The trial therefore provided an ideal source of material for molecular studies carried out in association with the University of Reading (see Molecular Studies), as well as a morphological investigation - the comparison of differences between plant leaves, flowers and other structures - and an opportunity to check the correct nomenclature of all the plants.

An initial search was made for every available known cultivar and during the course of the trial several newly raised cultivars were added. A number of Lavatera species were also planted, with several tender species being included for completeness and interest but which, as expected, did not survive winter in the cold, exposed conditions of the trials field. In all, more than 30 different species, hybrids and cultivars were evaluated. The Wisley woody trials ground had a brilliant display of colour and the Committee made the first of many visits in 1995. Revisits in successive years were made to observe the hardiness of the plants, their reaction to pruning and any reversion (returning to normal type) or signs of susceptibility to disease.

Showy shrubs
Of the woody tree mallows, the first recorded cultivar was pink-flowered Lavatera 'Rosea' introduced by Ladhams Nursery of Southampton about 80 years ago. It is a shrubby plant, to about 1.7m (51/2ft) in height, bearing pale purplish-pink flowers throughout summer. For many years this was the most widely grown shrubby Lavatera, hardier than the species L. olbia, of which it was originally believed to be a cultivar. Lavatera 'Kew Rose' was named about 10 years ago and is a much larger plant with bigger, brighter, pink flowers, as well as dark stems.

Lavatera 'Barnsley', possibly one of the most widely seen plants in gardens, is instantly recognisable in summer. Roughly 2m (61/2ft) tall, it is covered with white flowers about 8cm (3in) across with red centres, which turn pink as they mature and fade. The AGM awarded in 1993 was confirmed after trial.

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