New growth gives bright highlights of colour in the balcony planters. Bronze Nandina leaves flare bright terracotta when the light is behind them. The sage green Bergenia (veined with dusky purple on the mature foliage) has new leaves with blood red hearts. Young leaves on the Iceberg rose are a delicate but brilliant lime green. Japanese Autumn Fern (Dryopteris erythrosora) gives a glowing spring preview of the autumn colours to come. Even the usually unassuming houseleek (Sempervivum) has fanned out its rosettes to reveal a deep red line at the base of each succulent leaf.
Why are so many spring leaves brightly coloured when the mature leaves settle down to sombre shades of mid green? The new, lime green rose leaves are more soft and delicate than the mature, dark green ones and its easy to see that their colour simply darkens as the leaves thicken and harden. Unfortunately that’s obvious to every leaf eating bug or mammal too so young rose leaves are quickly smothered by aphids, chomped by weevils or browsed by deer (though obviously the last is not a problem we have to contend with here).
Red and gold colours appear in autumn leaves as the plant recuperates nutrients to store for the next season, breaking down green chlorophyll and accumulating red anthocyanin. Leaf eating beasts (big or small) recognise red tinged autumn leaves as less tasty and nutritious than fresh green ones so tender young leaves disguised as tough old ones stand a better chance of reaching maturity. Red leaves aren’t as efficient at photosynthesis as green ones so the protective colouring comes at a price but for many plants the temporary protection is a worthwhile investment. (This article in Plant Physiology assesses the costs and benefits). From the gardener’s point of view, spring foliage colours add interest and emphasise the changing season. Leaves free from damage by leaf-eating bugs are a bonus.
(Click on any photo to view the gallery)