Is the green rooftop trend really so different to ground level gardening?
Rooftop gardens are becoming increasingly popular. Now, this University of Melbourne guide gives you the low-down on the best plants for high places.
Gardening on rooftops and balconies is on the rise, and it’s quite different to gardening at ground level. Conditions can be punishing for plants as they cope with limited soil depth and extremes of sunlight, temperature and wind.
The University of Melbourne’s Green Infrastructure Research Group has developed a free guide to the most suitable plants for so-called “green roofs”. Based on 15 years of research at its Burnley campus (pictured), the 68-page guide provides proven plant palettes for five different types of roof gardens, ranging from low maintenance and shallow systems through to more complex high-rise gardens for wellbeing, pleasure and food production. It includes great photos of 180 plants, and also information on choosing the right soil mixes, calculating weight loadings and irrigation, as well as seven case studies. The plant lists are most suited to southern Australia. You can download the guide at girg.science.unimelb.edu.au/reports/
Species for Green Roofs
The Burnley Green Roof Plant Guide’s recommended plants for green roofs include succulents, native grassland species for biodiversity, perennials and shrubs for colourful flowers and interesting foliage, and plants for food production. Here are four of them:
Q&A
My five-year-old pomegranate bush flowers well each year but never sets fruit, unlike others in my neighbourhood. It’s protected from frost and is not an ornamental tree.
Margot Firth, Canberra
Pomegranates are sexually complicated, as different plants can bear flowers that are all functionally male or have both male and female parts or an intermediate form. Only flowers with full female parts produce good fruit. Many ornamental types, including dwarf ones, rarely produce fruit or it’s bitter or dry. Double-flowered forms are sterile. You need a named, proven cultivar such as ‘Wonderful’ or ‘Red Velvet’. Although self-fertile, fruit set is better with cross-pollination. Pollination is done by bees and other insects; transferring pollen with a soft brush can help.
Why do both my beautiful eucalyptus ‘Silver Princess’ drop leaves and die off at the ends of the weeping branches?
Catharine Simpson, Gold Coast
Because it is native to dry areas of Western Australia, this lovely tree dislikes humidity and wet summers. In the humid subtropics it is considered unreliable – prone to fungal dieback and early death. Spraying foliage with systemic Yates Anti-Rot might help. Neutrog’s POPUL8 supplies beneficial microorganisms that can improve soil and plant health.
Our mandarin, planted five years ago but not fertilised, looks healthy but never flowers. Why not?
Malcom Rough, Mt Nebo, Qld
All citrus can flower and fruit in their first few years but they need at least six hours daily of direct sun; in shade they won’t flower. They also need regular water and fertiliser. Use a quality citrus fertiliser, applying a little every month. Keep grass and weeds well away from the trunk; mulch with sugar cane mulch.
Send your questions to helenyoungtwig@gmail.com The best question for July wins a bundle of three stylish Le Sac gardening belts, valued at $228, to keep your tools, phone, and accessories at hand while gardening.
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