"Most ornamental plants in garden centres unattractive to pollinators"
An important factor in consumer choice is the range of varieties available for purchase. In the UK, garden centres are a key link in the supply chain between growers and private gardens. A new study from the University of Sussex is the first to determine the proportions of flowering ornamentals being sold that are attractive to flower-visiting insects.
Researchers surveyed six garden centres in Sussex, UK, each over two days in 2015, by making 12 counts of insects visiting patches of each ornamental plant on display for sale that was in bloom. To provide a consistent baseline among different locations, they brought with them and surveyed marjoram (Origanum vulgare) plants in pots, which are known to be attractive to a wide range of flower-visiting insects. The attractiveness of plant varieties to insects was then expressed in two ways: the absolute number and relative to that on marjoram (`marjoram score'), both per unit area of plant cover. In addition, they noted whether each variety was recommended as pollinator-friendly either via a symbol on the label, or by being included in the Royal Horticultural Society's `Perfect for Pollinators' list. Furthermore, they compared the attractiveness of plants that are typically grown for more than one year versus only one year.
The researchers surveyed 5974 plant varieties in bloom across the six garden centres. In each garden centre, the distributions of variety attractiveness were highly skewed to the right, with most varieties being relatively unattractive, and few varieties highly attractive to flower-visiting insects. The median attractiveness of varieties with a recommendation was 4.2 higher than that of varieties without. But, due to the large variation there was a substantial number of both poor varieties that had a recommendation and good varieties that did not. Median attractiveness of multi-year plants was 1.6 that of single year plants, with a similar overlap in distributions.
The study demonstrates the practicality of carrying out plant surveys in garden centres. Garden centres display large numbers of varieties for sale, most of which are in bloom. Furthermore, data gathered in garden centres appear to correlate well with data gathered in two previous studies in Sussex for plants established in gardens. Although it is unclear whether the varieties being sold in garden centres are a fair representation of varieties that are actually grown by gardeners, these results suggest that there might be considerable scope for making parks and gardens considerably more insect-friendly through judicious variety choices.
Download the full study from PeerJ.