Should garden retailers do more to ensure plants for sale are bee-friendly? This is the question being posed by Professor Francis Ratnieks from the University of Sussex's Laboratory of Apiculture & Social Insects, which has published a new study showing "most flowering varieties being sold to the public in England are relatively unattractive to flower-visiting insects".
Ratnieks' researchers surveyed 59-74 plant varieties in bloom across six garden centres - Notcutts Garden Pride, Wyevale, Staverton, Marchants, Hillier and Wych Cross, all in Sussex. "Our study aimed to determine how bee-friendly the plants on sale in garden centres are," he explains. "Most are not very much visited by bees and other insects. Therefore, there is great scope for improvement.
"In addition, garden centres are places where plants can be checked for how bee-friendly they are (the people who work in a garden centre could do this). More generally, there is scope for improving the supply chain in terms of bee-friendliness, and garden centres are part of this."
He adds: "If most private gardeners obtain most of their garden plants from garden centres, then on the whole urban gardens are probably not as friendly to flower-visiting insects as they could potentially be. There is considerable scope for making gardens more insect-friendly through judicious choices of varieties that are grown.
"We have also shown that the plants recommended as friendly to pollinators are only a few times better than the plants that are not recommended, presumably because these recommendations generally rely on casual observations or opinions."
In total, 325-2,339 insects were counted per garden centre. In all six garden centres "most varieties on sale were relatively unattractive to insects". Ratnieks says there is a 100-fold range in attractiveness among garden plants so there is ample room for improvement.
He suggests customers make "casual observations" before a purchase to give a rough indication of plant attractiveness, thus exerting consumer pressure by creating more demand for varieties attractive to flower-visiting insects, to which garden centres could potentially respond. Garden centres could also use this information to increase the proportion of insect-friendly varieties that are offered for sale and thus help pollinators in gardens and the wider environment.
The results show that the median attractiveness of perennial plants is 1.6 times greater than that of bedding plants. They also show that pollinator-friendly recommendations are "generally based on anecdotal experiences and opinions, rather than on empirical evidence (Garbuzov & Ratnieks, 2014a), which reduces their value".
But the median attractiveness of varieties with a beeor pollinator-friendly symbol on the label, or those present on the RHS "Perfect for Pollinators" list, is 4.2 times greater than that of varieties without such recommendations. Ratnieks maintains that the use of the word "perfect" by the RHS list is "inaccurate and presumably was chosen for marketing reasons".
Wildlife Gardening Forum trustee and RSPB wildlife gardening expert Adrian Thomas, who has written an inaugural Best Garden Plants for Wildlife report, says: "One of the most common questions in wildlife gardening is: 'What should I plant in my garden to benefit wildlife?' There is a plethora of lists available to gardeners in the UK offering suggestions, published in a wide range of wildlife gardening books and on websites.
"However, Garbuzov and Ratnieks (2014) concluded that of 15 lists they analysed, specifically of plants recommended for pollinators, they often included poor recommendations, omitted many good plants, lacked detail and were almost invariably based on their authors' general expertise rather than on empirical data."
By combining and averaging more than 6,500 scores from 29 experienced participants, the forum was able to create lists of top plants - a kind of "best plant charts" - showing which plants are consistently excellent (see box below).
Thomas adds: "Interestingly, there are some plants that are often recommended as being good for pollinators, such as primrose and pot marigold, that did not score highly in the survey. Conversely, some more unusual plants not normally recommended for wildlife were identified as being excellent and might enter the charts in future if more observations are made to confirm this."
He points out that the "ideal solution" to find out which plants are best for wildlife is a scientific study using trial plots with control conditions in several different locations around the UK, in which thousands of different plants and their cultivars are compared with each other.
Ratnieks' colleague Professor Dave Goulson is surveying neonicotinoid presence on garden centre plants. Ratnieks says: "If someone buys one or two plants that have been treated with an insecticide and brings them to their garden, it is hard to see how this will be harmful. First, the insecticide will soon dissipate. Second, the plant brought to the garden will only supply a small amount of the nectar and pollen being collected by a bee or a colony. I think it is a very different topic and that the two would not work together."
Meanwhile, a National Botanic Garden of Wales DNA study of the pollen collected by its honeybees has revealed that although 437 genera of plants were in flower in the garden during April and May, only 11% of these were used. All three hives used the same core set of native or near-native plants that are typically found in hedgerows and woodlands.
Commenting on the University of Sussex research, Notcutts chief executive Nick Burrows says: "Notcutts are passionate about biodiversity and helping our customers to understand and choose plants which are insect-friendly. We are always interested in any new research which might help us in developing and extending our ranges and we will be looking at the findings closely from the University of Sussex. Since July 2015 we have introduced additional insect-friendly varieties and have created specific wildlife and pollinator-friendly areas in our centres."
CHARTS BEST PLANTS FOR POLLINATORS
The Wildlife Gardening Forum's top-five "best plant charts" and average scores:
|1||Butterfly bush||Buddleja davidii||2.71|
|2||Yellow butterfly bush||Buddleja x weyeriana||2.63|
|4||Michaelmas daisy||Aster nova-angliae||2.57|
|1||Greater knapweed||Centaurea scabiosa||3.00|
|2||Round-headed leek||Allium sphaerocephalon||2.89|
|=4||Viper's bugloss||Echium vulgare||2.83|
|=4||Field scabious||Knautia arvensis||2.83|
|3||Round-headed leek||Allium sphaerocephalon||2.71|
|4||Lavandin||Lavandula x intermedia||2.70|
|2||Lamb's ear||Stachys byzantina||2.67|
|3||Comfrey sp.||Symphytum spp||2.67|
|5||Hedge veronica||Hebe spp.||2.57|
|3||Goldenrod||Solidago spp. and cvs||2.71|
|4||Common hogweed||Heracleum sphondylium||2.67|