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Exciting horticultural challenges at the Oman Botanic Garden

Volume 9 Number 1 - January 2012

Ian Oliver, Khalid Al-Farsi, Abdullah Al-Hosni, Salim Al-Makmari, Sarah Kneebone

The Oman Botanic Garden focusing on Oman’s native flora, is the first of its kind in the Middle East region. The Garden which is 420ha in extent is not far from Muscat the capital of Oman. It aims for excellence in botanical research, education and interpretation, cultivation and display of the unique flora of Oman.  A project of this magnitude obviously has its challenges, but the Living Collections Department faces more tests than usual. There are a total of 26 dedicated persons working in the living collections department – of this, 9 are University graduates.

The garden aims to house all 1,200 native, as well as the traditionally cultivated Omani plant species within its collections, with the vast majority housed in the living collections. Prior to the formation of Oman Botanic Garden in 2006, only very few of these native species had ever been propagated, and grown ex situ. Eventually all the native flora will be grown in specially constructed habitats that resemble the wild area the plants came from. While the habitats are constructed, the plants are cultivated in the nursery, ready to be planted out once the hard landscaped construction has been completed.

All relevant information about cultivating the plants is collected in the field so when the plant material is back in the garden the plants can be successfully propagated. This includes local climatic conditions, watering requirements, soil types, sun or shade conditions with success and failures recorded from the beginning of this project.

Field data helps to determine growing conditions for plants. Research and field work is a core function of the botanic garden, with over 200 field trips having been undertaken in the last 6 years to explore the landscapes of Oman and collect seeds and data on plant distribution, vegetation ecology, environmental conditions, and conservation status. Oman Botanic Garden uses BGBASE to enter data on a field computer during trips, to ensure that data is accurately recorded. Each new species collected in the field is awarded its own unique accession number which remains with that plant throughout its lifetime.  Seeds are dried, cleaned and counted in preparation for propagation, while cuttings and plants are processed as soon as possible by the horticultural team. All propagation data is also entered into BGBASE so that cultivation methods can be analysed for success and repeated.

Cultivation protocols are developed based on the detailed field observations

The nursery has state-of-the-art facilities including shade houses (9000 m2), outside hardening-off areas (3000 m2), 4 polytunnels (4000 m2), 2 glasshouses (2600 m2), a propagation house (700 m2 ), nursery offices, staff canteen and a meeting room.

The nursery uses a number of technical aids to lessen its impact on the environment. For example, a sophisticated computerized control system manages the whole nursery operation, by continuously monitoring outside conditions and adapting the water efficient cooling systems within the polytunnels and glasshouses to ensure a growing environment that is beneficial to the plants. 

Oman is primarily an arid country so efficient water use is vital.  A combination of automated irrigation drippers, ebb and flow matting and manual watering systems ensures irrigation is targeted exactly where it is needed. To reduce water usage even more, the team has tested a range of water-holding soil additive products. Sprinkling the water-holding soil additive products on the surface of some medium sized potted trees (Prosopis cineraria) has reduced their dependence on water by as much as 40% during the hot summer months.

Oman’s plants have attracted healers, crafts people, explorers and botanists for over 2,000 years.  The country is home to over 1,200 species of plants, with 80 species found nowhere else in the world.” 

The botanic gardens focus is on sustainable development, and therefore basic principles of sustainability are implemented to minimise damage to the environment and depletion of natural resources.

In order to reduce the carbon footprint, the use of peat, a non-renewable horticultural product, is to be radically reduced.  Since the start of the project, as more data about plant requirements has been established, the dependence on imported peats has been reduced by 50%; the peat has been replaced with local soils, sharp sand and gravel.  At present there are very few peat alternatives available in Oman. In the future, however, compost will be locally sourced using biodegradable green waste.

New cutting media have been developed that suit the soil conditions in the areas from where these plants originate.

Plant health is important in the fight against pests and diseases. Chemical use is minimised and is based on low-toxicity. The use of strong organo-phosphates is not permitted on the site. Instead more environmentally friendly pesticides, like Indian neem cakes (Azadirachta indica) and lemon and chilli grass extracts, are used. In the future it is hoped that biological control agents will be used to effectively combat all pests and diseases.
Integrated pest management helps reduce pesticide use. Good hygiene is of paramount importance to good plant health. Infestation levels are continuously monitored. Different coloured insect sticky traps help to monitor and remove pests.  

Air pots have had a positive impact on growth rates and longer term survival of large trees and shrubs.  This innovative product comes in perforated pre-moulded sheets of recycled polyvinyl, ready for assembly on-site. The perforations allow for air-pruning so protruding roots are effectively dried out when they come into contact with the outside environment.  The air flow also allows the roots to stay cooler, which is vital when temperatures in the nursery can exceed 49°C during the summer.  Sizes used are 45 litres, 150 litres, 600 litres and 1000 litres. The young baobabs (Adansonia digitata), are cultivated in air pots containing several hundred litres of specially prepared growing mixtures. Baobabs in Oman can eventually reach a height of 15 meters. In the Middle East baobabs are unique to southern Oman and a few areas just across the border in Yemen. Many translocated trees are potted up in air pots holding 1000 – 1500 litres of growing medium.

Over 20% of Oman’s plants are threatened through environmental issues such as over-grazing, development and habitat destruction

Translocation and rescue of mature trees from degraded or disturbed sites is ongoing. The team works in conjunction with the Ministry of Transport and visits road construction projects, water pipeline sites etc. to identify large trees for rescuing. Large trucks and construction machinery are used to excavate mature specimens that would otherwise be destroyed. The survival rate is about 60%. As much care as possible is taken when transporting these large tree specimens, for example by wrapping the roots in geotextile cloth during transportation back to the nursery in Muscat where they are immediately planted into large air pots. Some of the largest trees are 5m tall, for example one Juniperus excelsa which is several hundred years old, and two Olea europaea. A large desert rose, Adenium obesum measuring over 3m in height, has also been rescued.

It is essential that climate controlled shade houses are provided for the plants as without them they would be stunted or die. Plants respond best to 50% shade. Some of the plants will eventually have to be hardened off so that they can be planted outside in the harsh desert conditions.

Through the use of new products and experimental horticultural techniques, the nursery now houses 100,000 plants and approximately 360 species and is the largest documented collection of Arabian plants in the world.

Ian Oliver
Khalid Al-Farsi
Abdullah Al-Hosni
Salim Al-Makmari
Sarah Kneebone

Oman Botanic Garden
Diwan of Royal Court,
P.O. Box 808, Muscat 122,
Sultanate of Oman