Planting for winter-active invertebrates

Planting for winter-active invertebrates

Many planting schemes with an ecological input specify that only native species should be used, and for very good reasons too. There is a problem with native planting, however, in that indigenous trees and shrubs in the UK are limited in number and very few of them provide a food resource for invertebrates during the winter months. Climate amelioration means that more invertebrates are going to be active during the winter, especially in towns and cities. But will there be enough food to sustain them?

One of the best known winter-active pollinators is the buff-tailed bumblebee (Bombus terrestris); winter colonies are present mainly in the south of Britain. A number of other bumblebee species are also winter-active. But bumblebees are not the only pollinators to be encountered in winter. Hoverflies and other fly species can also remain active throughout the winter months if conditions are mild enough.  Among the hoverflies, the fairly large honeybee-mimicking hoverflies (Eristalis tenax and E. pertinax) can be seen sunbathing or nectar-collecting on flowers, as well as flesh flies (Sarcophagidae) and green bottle flies (Calliphoridae).

Research undertaken by the Royal Horticultural Society (Plants for Bugs) has shown that non-native shrubs (including exotics from the Southern Hemisphere) support only 10-20% fewer invertebrates than British native species.

By flowering later (and earlier) in the year than most British species, non-natives extend the season, providing nectar and pollen for any insect species that happen to be active.  So while it makes perfect sense to weight urban planting towards species native to Britain, there is much to be said for also including flowering plants from other regions of the world.

So which are the best non-native species to plant that will sustain winter pollinators? Opinions vary, but the following four species are good examples:

• Winter Cherry (Prunus x subhirtella). This hybrid originates from Japan and many varieties of it exist. Flowering starts from November onwards and continues right into spring. It’s white to pink flowers are loved by bees. This species can be grown in any moist but well-drained soil in full sun. It makes an excellent specimen tree.
• Winter Jasmine (Jasminum nudiflorum), a deciduous (usually climbing) shrub originating from western China. It grows best in well-drained soil in a sheltered position, either in sun or partial shade.
• Oregon Grape (Mahonia aquifolium) originates from western North Africa and starts flowering from November onwards. The scented, yellow nectar and pollen-rich flowers are a magnet for bumblebees, honeybees, hoverflies and other flying insects. This species tolerates a wide range of soil conditions but does best in humus-rich, moist but well-drained soil in semi-shade.
• Laurustinus (Viburnum tinus). This garden favourite is a large, evergreen shrub which grows to to 3 metres. It has dark green, oval leaves and clusters of small, creamy-white flowers (pink-tinged when in bud). It originates from the Mediterranean region and its flowers are usually present from November to March. Laurustinus grows best in well-drained/light, moist soils and is shade tolerant. It is an excellent choice for hedging or screening, but can also be planted as a small specimen tree in sheltered positions.

Some other good bets are:  Abelia (Abelia x grandiflora), Coast Silk Tassel  (Garrya elliptica), Cornelian Cherry (Cornus mas), Hebe (Veronica spp.), Japanese Aralia (Fatsia japonica), Sweet Box (Sarcococcus confusa), Wallflower (Erysimum spp.), Winter Heather (Erica carnea), Winter Sweet (Cimonanthus praecox) and Winter-flowering Honeysuckle (Lonicera fragrantissmima).

 

Sources / links:

• ‘Urban Pollinators’ | http://urbanpollinators.blogspot.com/2013/12/winter-flowers-for-bees-and-other.html
• Stelzer RJ, Chittka L, Carlton M, Ings TC (2010) Winter Active Bumblebees (Bombus terrestris) Achieve High Foraging Rates in Urban Britain. PLoS ONE 5(3): e9559. https://doi.org/10.1371/journal.pone.0009559 https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0009559
• ‘Plants for Bugs’ | https://www.rhs.org.uk/science/conservation-biodiversity/plants-for-bugs

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