How safe are garden centre plants?

Sarah Brown unpicks the recent worrying research about pesticide residues in garden centre plants...
Flowers in Ryton gardens

In the last edition of The Organic Way, Judith Conroy discussed the issue of pesticides in Garden Centre plants. Since then, recent research from the University of Sussex has confirmed her fears.

Nearly three quarters of the plants bought by the research team were tested positive for insecticides. Worryingly, many of these plants – such as lavender, bergamot and honeysuckle –are sold as ideal for pollinators.
We caught up with Professor Dave Goulson, who led the research. He explained: “We bought flowering plants from a range of major outlets; Wyevale (the biggest garden centre chain in the UK), Aldi, B&Q and Homebase. We deliberately bought plants that are known to be attractive to bees and butterflies; most of them had a bee-friendly logo. We screened the leaves, pollen and nectar to see if they contained pesticides.
We found that most of these plants contained a cocktail of pesticides, usually a mixture of fungicides and insecticides. Seventy six percent of them (22 out of 29) contained at least one insecticide, and 38 per cent contained two or more insecticides. One flowering heather plant contained five different insecticides and five different fungicides – a veritable toxic bouquet.
Seventy per cent of the plants contained neonicotinoids (insecticides that are notorious for their harmful effects on bees.) These included the three neonics banned for use on flowering crops in the EU (for the technically minded, 38 per cent contained imidacloprid, 14 per cent contained thiamethoxam and one contained clothianidin).”
Finding the source
So where do these chemicals come from? And how are they appearing in flowers, despite being banned throughout the EU?
It appears to be an issue somewhere down the supply chain. Many garden centre plants are bought in from abroad. The chemicals are embedded in their potting compost and can last for up to a year, especially in cooler climates such as the UK.
The three neonics listed by Dr Goulson – imidacloprid, thiamethoxam and clothianidin – have been banned since 2013. This moratorium, however, does not apply to non-flowering crops or to ornamental flowers - in the year in which they are to flower. Even with this deliberate time constraint, Goulson’s team still found evidence of these three pesticides.
Dr Julian Little, bee care spokesperson at Bayer, which makes the legal neonicotinoid, thiacloprid, points out that clothianidin, for instance, has never been registered in the UK for ornamentals "so in principle it shouldn't be there". Dr Little then goes on to say “No doubt Dr Goulson thinks they mean something significant but I suspect levels are so low that exposure to bees is going to be negligible. I can't account for why some of these (pesticides) are showing.”
To which, Goulson responded: “The concentration of the pesticide is of course important. Modern analytical techniques are very sensitive and tiny amounts can be detected.
The concentrations of neonicotinoids typically found in the nectar and pollen of treated crops such as oilseed rape are in the range 1-10 parts per billion (ppb).
“Compare this with the concentrations found in the ‘bee friendly’ flowers, where we found imidacloprid at up to a maximum concentration of 29ppb, clothianidin at 13ppb and thiamethoxam at 119ppb. In other words, concentrations far higher than those known to harm bees.
“Exposure to these concentrations has been found to impair bee navigation and learning, reduce egg laying, lower sperm viability, and suppress the immune system. In a study with bumblebee nests we found that giving them pollen with just 6ppb of neonicotinoid reduced nest growth and resulted in an 85 per cent drop in the number of new queens produced.”
The organic challenge
Organic growers recognise the need to attract beneficial insects. Not only do they help pollinate plants, but they add to the important biodiversity within the growing area. Mixing your planting - adding flowers and vegetables together - feeds and sustains this insect life.
But how can you source your organic plants? The first choice is growing from seed, or taking cuttings from friends and neighbours. You can also search for organic nurseries and suppliers online.

Many independent nurseries are pesticide-free. Finally, if you have to go to a garden centre, then make it B&Q or Aldi and tell them you support their pledge to phase out neonicotinoids. Lobby your own local garden centre. Show them the Sussex Research paper and ask if they can source plants without pesticides. The bees would thank you for it.
As Goulson says:
If I’m buying plants to encourage wildlife, I don’t want the lingering worry that I might be accidentally poisoning my bees, hoverflies and butterflies. I don’t use any pesticides in my garden – I simply don’t need them. And I don’t want to bring them in accidentally.
Further reading

Top 10 flowering plants for pollinators and other beneficial insects
Buddleja, Comfrey Symphytum officinalis Cowslip Primula veris. Common poppy Papaver spp Cornflower, Centaurea cyanus Fennel Foeniculum vulgare. Foxglove, Digitalis purpurea. Forget-Me-Not Myosotis arvensis. Greater knapweed, Centaurea scabiosa Lavender and Thistle Cirsium vulgare.
A more complete list has been compiled by the British Bee Keepers Association. It covers plants by season, so your planting can support insects who emerge early in the year and throughout the summer into autumn. Go to The British Beekeepers Association Learning section, Gardening for Bees.