Questions around plant imports and provenance are rising up the agenda thanks to the disastrous impact of diseases such as ash dieback, which was brought in from the continent.
The RHS will campaign from April 2014 to urge travellers not to bring biosecurity-risk fresh produce and plants back in their luggage. Gerard Clover, the new RHS principal scientist responsible for plant health, formerly managed the Plant Health & Environmental Laboratory in New Zealand's Ministry for Primary Industries.
Biosecurity laws in Australia and New Zealand are strict, and Defra secretary of state Owen Paterson said how impressed he was with the quarantine system down under when launching the Government's "Stop the Spread" garden at the RHS Chelsea Flower Show in May. This could lead to less choice of plants in the UK.
RHS president Sir Nicholas Bacon says "many British nurseries are struggling with increasingly aggressive European competition and the UK being increasingly threatened by issues such as the growing number of pests and diseases from abroad".
British growers perhaps have a different view of international trade to continental nurseries because the UK does not export much. But more and more growers are now exporting.
Seiont Nurseries manager Neil Alcock says his nursery now exports 20 per cent of production and the trade has helped move product during poor-weather UK seasons.
Licensed plants that are not readily available overseas are in demand, particularly in France, Germany, Poland, Holland and Belgium. But he says it is "far easier" to import from the USA, South Africa and Australia than it is to export there.
On biosecurity, he adds: "It's down to volumes and the integrity of the people involved. Sudden oak death and ash dieback must have helped UK tree growers because home grown is less likely to have infection."
Graham Spencer, owner of international plant breeders' agent Plants for Europe, says the idea of the RHS campaign is good "but it's dangerous to say that imported plant material is bad. If that goes too far people might think any plant from the Netherlands or Italy is dangerous".
British Protected Ornamentals Association chairman Ian Riggs promotes the "Home Grown" scheme for growers using a Union Jack leaf emblem on plant labels. "British-grown matters," he says. "Slower-grown UK product has travelled less distance and has been handled less, and that means a better product for the consumer."
He points out that poinsettias are grown at 10 per square metre in UK glasshouses and 14-16 per square metre in Holland. This means Dutch product is "less branched and more upright - and it's grown a lot faster so it won't last as long".
Peter Eastwood Nurseries owner Peter Eastwood says Home Grown stickers on his poinsettia in a trial at Manor Nursery saw double the number sold compared to an adjacent bench filled with non-stickered poinsettia.
All his pots now have the Home Grown logo. "People like to buy British," he says. "Our pots even say 'grown in Sussex' in even bigger print. The public are more aware of food and plant miles and the effect on quality of shipping things like poinsettia."
However, UK poinsettia growers cut production this year as fuel costs rose and because investment in new glass is costly (HW, 8 November), meaning more imports. In Christmas trees too, UK growers cannot meet supply because not enough were planted a few years ago when prices were lower.
British Christmas Tree Growers Association chairman Harry Brightwell says: "There's still not enough home grown from the UK market and exports are needed to meet demand. But if there becomes an oversupply, it will hit prices."
Buckingham Garden Centre general manager Mike Easom says keen gardeners are bothered about where their plants are from but impulse buyers do not care. More people ask him about provenance "in light of ash - that's blown it up. People want to have the confidence that it's British-grown."
Most big retailers say they will buy British if plants are available at the right specification. Sainsbury's plant technologist Nicola Phillips says: "Our poinsettias are always 100 per cent British and grown in six sites across the UK from the south coast to Scotland."
Waitrose, Marks & Spencer and Homebase use mostly UK suppliers, while Asda, Tesco, Morrisons and Lidl are believed to use varying degrees of imports.
Spencer says: "In a single European market, plants move around. We need it to encourage movement of goods so that gives us better access to a wider variety of plants, coupled with an effective plant-health system."
But he warns that new pests and diseases thriving in Britain because of more international plant trade and global warming "may change the perception" of UK gardeners towards imports.
The system "is not being implemented uniformly in some EU countries, especially in southern Europe", he adds. "They're able to get away with more than we do here." A planned referendum on EU membership for 2017 might change all this.
Plant production - Home-grown stock catches up level of imports
The value of UK plant production has caught up with the value of imported stock over the past few years, probably because of currency fluctuations.
UK production of plants and flowers is worth £1,048m, with imports at £1,055m. But two-thirds of imports are bouquets, while two-thirds of British production is hardy nursery stock and almost one-third is protected bedding. The remainder is bulbs.
Indoor plant imports have been steady at £100m-£112m since the Groundforce boom in 2002. Outdoor plant imports are the same as 2003 at £55m. Trees are at £63m. Bulbs imports have doubled in a decade to £89m.