Purple leaves, which are coming into their full glory now, will make red and yellow flowers seem more intense, and add more depth to a border than any green can, so they are particularly suitable for the Jewel Garden. I was first struck by how effective purple foliage can be in the garden of Kiftsgate Court near Chipping Campden in Gloucestershire. The way that purple hazels were coppiced there influenced me dramatically. Coppicing the shrubs - in other words regularly cutting them right to the ground - produces vigorous new shoots that carry extra-large leaves. After that visit to Kiftsgate I bought some purple hazels, Corylus maxima ‘Purpurea’, and sat back to watch them become healthy plants.
Our coppice is made up of 73 green hazels, Corylus avellana, which all grow lustily, so I assumed their purple cousins would perform just as well in the Jewel Garden. No such luck. For years they hardly grew at all, so I eventually replanted them in a nursery bed, where, to my surprise, they flourished - not only producing purple leaves but also pink- and magenta-tinged nuts. Finally I worked out what the problem was.
Although planted in an open border, they were nevertheless being shaded out by the vigour of the annuals that I grow in those beds, particularly Atriplex hortensis var. rubra, the purple orach, which is a prodigious self-seeder. It took me a while to realise that an annual with a life of just a few months could crush the will to live in a small tree. In the end I bought four more much larger purple hazels and planted them in exactly the same spot and they thrived - because their foliage was never competing for precious light.
However, I don’t coppice right to the ground because the young shoots would face the same problem as the first batch of plants, so I selectively prune a third down to the ground every winter, leaving enough up in the light to nourish the roots. It works well.
If they had green leaves they would probably have coped with the lack of light but the red layer of pigment over the green of the chlorophyll means less photosynthesis and therefore less nourishment. In short, purple-leaved plants need more pampering than green-leaved ones and, if they are to grow at all strongly, more light.
As well as the hazels in the Jewel Garden borders we also have a few other purple-leaved shrubs to act as a backdrop to increase the intensity of colour, especially in late summer. There is the smoke bush, Cotinus coggygria ‘Royal Purple’, which has excellent burgundy leaves with a touch of brown. C. c. ‘Velvet Cloak’ is good too. I also have a purple elder, Sambucus nigra f. porphyrophylla ‘Guincho Purple’. This is so vigorous it will take a really hard prune every year, outgrowing the competition for light around it, but the cotinus need plenty of light.
You do not have to use shrubs for your foliage plants. I also grow Lysimachia ciliata ‘Firecracker’, a perennial with chocolate leaves and little yellow flowers. It is superb if you have dampish soil, although it flops badly in dry conditions. If happy, it spreads like wildfire and needs reducing by as much as three-quarters every few years to keep it under control.