There’s a trial of amaranthus (love-lies-bleeding) at RHS Wisley this summer. The rectangular plot is a patchwork of butterscotch-brown and beetroot-red splashed with lime-green. The stems are two inches thick at the base and many of the 30-odd varieties have topped four to five feet in the richly-fed trial beds found on the south-facing Portsmouth Field.

Nearby, there’s a trial of celosia, vertically challenged plants in garish shades of yellow, red and orange. I loved these tactile plants as a small child. But now they make me wince, although I have been taken with a graceful dark-leaved taller mixture called ‘Thompsonii Magnifica Mixed’ (available on the internet from Seeds-by-Size) that’s between two and three feet high. Thompson & Morgan’s ‘Flamingo Feather’ is a taller green-leaved selection with lots of small upright rose-pink spikes.

These two feathery-flowered ‘little and large’ genera are close relatives and once you examine the flower structure it’s obvious. I grow amaranthus every year and I am enthusiastic about them: some fellow committee members would say obsessed. But amaranthus tends to sulk in cool summers and my garden has been under cloudy skies and a strong south-westerly for months. However, the south-eastern corner of Britain (including RHS Wisley) has been basking in hot, dry sunshine – very annoyingly. So down there, where they have been doing a rain dance for weeks, the amaranthus are hugely impressive.

There are 60 species of amaranthus and in warmer parts of the world this plant is used as an important food crop. In parts of Asia they harvest the leaves like spinach. In Greece Amaranthus viridis (green amaranth) is boiled, and served with olive oil and lemon as an accompaniment to fried fish. It’s called vleeta – and I’ve eaten it obliviously. Apparently the Greeks stop harvesting this wild-grown plant when it starts to bloom at the end of August.

The tassels of A. viridis live up to their name: they are a pale-green and (like all green flowers) they flatter vibrant flowers, especially the deep-red dahlias. Amarantos is Greek for ‘the never-fading flower’ and amaranthus will last for months whatever the weather.

In Asia and the Americas they harvest the nutritious, grainy seeds rather than the leaves. The seeds are plentiful, the plant grows in dry conditions and the grain contains large amounts of protein and essential amino acids.

Amaranthus seeds are reported to have 30 per cent more protein value than rice, wheat flour, oats and rye so it may well become an essential crop of the future.

In recent years, two varieties with dark flowers and leaves have been bred. One is ‘Marvel Bronze’ and the other ‘Velvet Curtains’. They are similar, but I think ‘Velvet Curtains' has thicker textured foliage. Chiltern Seeds do a similarly dark and handsome selection called ‘Oeshchberg’. But if you like the traditional green-leaved love-lies-bleeding, Johnsons sell ‘Crimson’. The long, lavish flowers are pink-red.