Plant of the month: May

Euphorbia polychroma

Did you ever see anything so like summer?

I grow many euphorbias, which love my dry, sandy soil. E. martinii for its smoky flowers and burgundy stems, the slightly tender E. mellifera (clobbered by this winter's frosts but I hope recovering), E. cyparissias 'Fens Ruby' which I'm forever having to dig out of places it shouldn't be, but I forgive it anything for its feathery burgundy foliage in spring; E. myrsinites to snake around the skirts of other plants, and a few self-seeded E. robbiae from who knows where.

I love them when they're flowering, but for the rest of the year they can look a little gaunt, I find. That's fine in my jungle garden where wierd and gaunt-looking plants abound, but not so happy in the cottagey riot of summer flowers elsewhere. So I tend to hide the foliage behind other things.

Not so Euphorbia polychroma. This is the Jeeves of the plant world: a plant which in a garden full of the unruly, the mischievous and the downright contrary always, always, knows the right thing to do.

In spring, just when you need a foil to your muscari and crocuses, the clear lime-green foliage starts frothing up from the ground. Gradually it expands like a delicate bubble: never too quickly, as it would never be so rude as to outshine the tulips or the daffodils, but just quickly enough to provide a green backdrop at just the right scale.

Then finally, when it reaches a neat and tidy naturally domed shape of such perfect uniformity that nobody believes I don't clip it, and just when the tulips are going over and you're starting to want something else to look at, the acid yellow flowers appear - in reality, of course, bracts that attract attention to the inconspicuous true flowers in the centre. They are of a brilliant purity that reminds you of the sun even when there isn't any in the sky: and when there is, they glow with a luminescence of sunshiny joy that they make me smile every time I look at them.

They last a satisfyingly long time but not so long as to outstay their welcome. I grow an apricot rose behind it, and the brightest yellows last, obligingly, just long enough to combine rather fetchingly with the orangey shades of the rose. Then, like all good performers, it knows when to stop hogging the limelight and retires gracefully into the wings as the bracts fade back to green. Even then it judges its role perfectly, providing a green of just the right shade to set off the daylilies, rock roses and potentilla that also tumble around it.

There it stays, good-natured and accommodating to the last. It keeps its dignity and poise well into winter and sometimes into spring too if heavy rains haven't bent the branches out of shape, looking terribly sculptural with a good frost.

The only time it's even remotely demanding is when you need to snip away each branch right to the ground in early spring just as the new shoots come through (wearing gloves, as one of this plant's few faux pas is to emit an irritating sap when pruned). Then you wait for the whole thing to happen all over again. There's no better-behaved plant in my garden.