All garden designers have plants that they prefer to use because of their visual impact on a landscape or a garden setting. But, as Natural History Museum scientific associate Dr Mark Spencer reminded delegates at the start of the Palmstead Nurseries annual soft landscape workshop last week, plants chosen for their aesthetics often conflict with the wider biodiversity agenda.
Spencer explained that some of Britain's most popular greenery choices are in fact major non-native invasive species that are causing significant environmental problems. One such example he gave was shrubs with berries, such as cotoneasters. "We want to plant something with berries because there's a strong driver that it's good for birds. However, there are impacts we might not know about."
Another example of when garden designers' good intentions might go awry is when they specify certain plants for the benefit of bees and other pollinators, said Spencer. "We are very good at planting plants for them but we don't really understand these organisms. Lots of them (bees) are polylectic - they eat pretty much anything. But solitary bees are oligolectic - they only like a few species. Lots of bees have selectively evolved with the plants that they feed on."
Spencer noted that understanding the evolution of plants handily gives some indication of how well bees are going to work with them. "Look at European flora. Oligolectics are more attracted to plants with a European heritage," he said. He therefore advised his audience that while it is "incredibly difficult to predict the consequences of our actions" we can nevertheless help "future-proof" our environment by taking note of the origins of plants and incorporating science into our decision-making process.
He concluded his talk by reminding his audience that despite the fact that British plants are perceived by some as being "boring," native (and near-native) species such as heather are "superb for insects".
Plants and health
Collaborative garden designers Jackie Herald and Shenagh Hume, who work with Allergy UK and specialise in low-pollen gardens, told delegates 18 million people in the UK suffer from hay fever and 50 per cent of children under the age of 18 have one or more allergies. Given this, the horticulture industry should be doing its utmost to incorporate low-pollen plants into its designs, they suggested. However, it is currently unintentionally compounding the issue through its frequent use of wind-pollinated trees such as silver birches and London planes.
Hume, a former allergy and asthma nurse at Guy's Hospital in London, used the UK's capital city as a case in point. "Years ago when I lived in London Bridge the area was derelict and undeveloped. With the advent of City Hall the whole area has been regenerated with landscaping dominated by silver birches. Add to the mix traffic pollution and ozone and there is huge potential for an increase in respiratory allergies."
Helpfully, the pair gave delegates some useful tips on how to keep pollen to a minimum (see box) and also drew the audience's attention to the OPALS (Ogren Plant Allergy Scale) system developed by Thomas Ogren in the USA that uses a scale of 0-10 to measure plants' allergenicity.
University of Reading RHS research fellow Dr Tijana Blanusa revealed how her research focus is on pollution, another known cause of health problems. Examining how plants sequester particles of air pollution, she has found that larger plants with a more complex structure usually provide more environmental benefits. "If we look at a surface of a leaf and see how it takes up the gases in the environment we can see that if you chose a more active plant, with more openings in the leaves, it has potential to take up more pollutant gases such as carbon monoxide, ozone and nitrous oxides."
Green infrastructure and planning consultant Anne Jaluzot emphasised how trees' cooling effect must play a more important role in urban environments. She cited Garibaldi Street in Lyon, France, as an inspirational case study. With the need to mitigate pollution, absorb excess rainfall and cool down temperatures in mind, the street is being rebuilt to incorporate new soft and hard landscaping as well as water-harnessing facilities and is "an ideal model for the future", she said.
Plants and well-being
Garden designer Jinny Blom discussed some of her best-loved projects with workshop delegates. These included her 2013 B&Q Forget-Me-Not RHS Chelsea Flower Show garden created for Sentebale, a children's charity founded by Prince Harry and Prince Seeiso of Lesotho.
Highlighting the way in which the show garden successfully raised awareness of Lesotho's HIV and Aids epidemic, Blom said: "If you want to raise awareness of something good it really is worth it because even though it's only for four days I did the equivalent of £9m worth of press about Lesotho, HIV and Aids. In some ways I think Chelsea can be a vehicle for things that concern us."
HTA head of horticulture Raoul Curtis-Machin also emphasised the key role that the horticulture industry can play in addressing some of society's most pressing issues. Referring to the new cityscape in Leon, he said: "I can't picture anyone in Defra who knows anything about this so they need us to help them."
He also suggested introducing a new ratings system for plants to rank their allergenicity as well as what they can do for the environment, health and well-being. "If we can get that into the planning system in a practical and simple way it's going to help everybody and we don't necessarily have to hit a brick wall with Government."
Pollen Reducing impacts and its harmful effect on urban allergies
- Increase plant biodiversity (avoid monocultures).
- Avoid mass use of male individuals of dioecious species (select females for low pollen levels).
- Choose low-pollen emitting plants that are 0-5 on the OPALS scale.
- Avoid large focal pollen sources by respecting planting distances.
- Obtain expert advice when selecting suitable species (when possible, select funnel- and tubular-shaped and double-petalled flowers).
- Establish local authority by-laws to ensure sufficient time for planning.
- Carry out regular maintenance - mown lawns, clipped hedges.
- Celebrate with more flowers and colour - "the more soft landscaping you can include the better".
Source: Hume and Herald
Xylella fastidiosa Pathogen poses genuine threat to industry
Landscapers and garden designers should keep a paper trail of where their plants are coming from because of the new threat posed the bacterial pathogen Xylella fastidiosa, Raoul Curtis-Machin has warned. "Up until this point it was really just wholesale nurseries that had to play by the plant passport rules," he said. "This new disease has everyone so worried that the recommendations have been extended to professional plant operators, including landscapers. This one is the first of its kind that has got us all worried. It can put us out of business overnight."