Our flowering season at Boningale was preceded as always with our dwarf tulip and crocus bulbs, bring a short flash of colour before the main action started. A few dwarf alpine bulbs are a great and economical way to liven up a standard green roof.
Then we had the primulas – this year the primrose (P. vulgaris) has been more dominant than the cowslip (P. veris) probably due to the fairly mild spring. The daisies (Bellis perennis) have also been out in force, undisputed champion for longest flowering season, and the leaves stay pretty green through the winter as well.
Coming second place after the daisies for most underrated green roof plant (-or maybe third, after late flowering delosperma) is Alyssum saxatile, a beautiful early flowering companion to sedum on my mountain roof.
The rainbow array of colour is now starting to develop, with some campanula, Viola tricolor, silene (red campion) and lychnis (ragwort) leading the race. Of all the species mentioned only the latter two get a little bit tall, so if roof-top maintenance is not your cup of tea then there is no reason why some of these shorter plants shouldn’t be livening up your plant palette, even if they are nestled in among a backdrop of sturdy low-growing succulents.
All the received wisdom is that green roofs are best planted in spring or autumn – really what they need is regular watering during establishment. If you are planting during an unusually hot and dry spring or autumn , just make sure that your new green roof gets a good watering at least once a week. And look forward to a colourful season!