

In theory green roofs that are planted with sedums require no maintenance. The growing medium, described as substrate rather than soil, looks like lumpy brick dust that seems too impoverished to sustain anything. Sedums are succulents, however, and thrive in such conditions, especially without competition from other plants.

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So far, so good; but dandelions, thistles and – worst of all – buddleia bushes, with seeds that float on the wind, have other ideas. These weeds can appear in large numbers in spring. Seven years’ experience shows it is the weather that plays a crucial role in subsequent maintenance. Although the invaders are often in miniature because of poor nutrition, the thistles and dandelions do flower and produce seed if there is regular rain, but with a long enough dry spell, they shrivel and die.

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The exception is the buddleia, which withstands the harshest conditions. These seedlings have to be pulled out each spring to protect the lining of the roof – thankfully, not a difficult task in loose brick dust. This weekend a trip up the ladder revealed a glorious forest of sedum flowers and not a single weed in sight. The heatwave has at least done wonders for this part of the garden.