City Trees

The flowering period is only up to three weeks every year but proves a stunning spectacle. Spin the globe, and at the right time of year, you'll find blue jacaranda (Jacaranda mimosifolia) lighting up streets and parks with its blue-purple flower panicles in every subtropical or warm climate, from regions within Australia to Myanmar to India to South Africa to Spain to Southern California. Even regions with an occasional light frost may support established blue jacaranda trees. Blue jacaranda can grow in part shade but it flowers best in full sun. Though its distribution as a cultivated tree is vast, blue jacaranda's native range is limited to southern Bolivia and northwestern Argentina. As is often the case for trees occurring in such a narrow range, the native blue jacaranda population in these South American pockets is considered vulnerable. It should be noted that in some of the same places it is celebrated (parts of Queensland, Australia and in Pretoria, South Africa, for instance), there have been concerns about jacaranda's invasiveness and displacement of native plants in those regions. In such places, municipalities have had to strike a balance between these concerns and the pow- erful public affinity for the showy jacaranda. Sitara Gare is the Planning Project Arboriculture Coordinator for Brisbane City Council, Australia, and a jacaranda fan. "Here in subtropical Brisbane, jacaranda is tolerant of periodic drought," she says. "It is often planted as a park feature tree in avenues or groups due to its iconic showy carpet of lilac-blue, trumpet-shaped flowers that drop in November before it grows its new leaves. The flowering period is only up to three weeks every year but proves a stunning spectacle." Gare says that the mature height of jacaranda in Brisbane can vary depending on the site conditions, from as small as 9m (30 feet) up to 25m (82 feet). She says that its success as a street tree is largely dependent on the amount of growing space and the site conditions it's given; like so many tree species, jacaranda is most suited to larger sites where the tree can benefit from well- drained soil. "I have found that many jacarandas planted too close to footpaths fail to thrive, become stunted, or sometimes even enter early senescence due to the stress of the constrained site conditions," she says. According to Gare, Jacaranda mimosifolia does not like exposed or windy sites; as a young tree it needs to be staked to keep it growing straight and strong. Jacaranda does benefit from forma- tive pruning at years three and seven after planting. It can be grown from both seed and cuttings. "Jacaranda trees have an inner canopy that is defined by a different type of bark," Gare says. "The trunk and major scaffolding limbs have a rough bark, but the inner canopy has a smooth grey bark. Up to ten years ago, within the local arboriculture industry these smaller limbs were pruned because they were thought to be a type of epicormic growth. However, experience has shown the inner canopy need not be pruned unless for health or other structural reasons." Jacaranda shares its taxonomic family, Bignoniaceae, with catalpa trees (Catalpa spp.) and trumpet vines (Campsis spp. and Bignonia spp.). urban-forestry.com 37

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