Cobaea scandens Purple

A climbing annual that will put on four to six metres in a single season and cover a wall or a pergola from one packet. The flowers are big bells framed by a green leafy calyx, which is the saucer the common name refers to.

The colour show is what makes it. A bud opens papery lime-green, develops violet stripes over a day or two as the pigment comes through, then deepens to a rich varnished purple, and because the plant carries flowers at every stage at once you get green, striped and purple bells on the same vine. There is a sweet musky scent in the evening, a hangover from being bat- and moth-pollinated in its native Mexican mountain forest.

Two things will lose you the display. It must be sown in January or early February to have time, and it needs real warmth to germinate. Flowering does not start until August and runs to November, so a plant started late gives you a great deal of vine and almost no flower before the frost takes it. It is also no use cut; the bells collapse in a vase within a day. Enjoy it where it grows.