Botanical Dahlia (botanical style)

Dahlias come from the uplands of Mexico and Central America, where the Aztecs grew them. They reached the botanic garden in Madrid in 1789 and were named after the Swedish botanist Anders Dahl. Like daisies, they belong to the family Asteraceae, so each bloom is really a head of many small florets packed together. Breeders turned them into singles, pompons, waterlilies and cactus types, whose narrow petals roll back along much of their length. It's also Mexico's national flower.

Dahlia tubers are tender, so start them in pots under cover in March or April, or plant them straight outside in May once frost has passed. Give them sun, rich soil and a stout stake, and protect young shoots from slugs. Pinch out the growing tips for bushier plants, then deadhead weekly and they'll flower from July until the first frost. When frost blackens the leaves, either lift the tubers to dry and store somewhere frost-free, or, in milder gardens, leave them under a thick mulch.

An orange cactus dahlia fills this study, with a bud and leaves alongside, all on a cream ground. The spiky, quilled petals of the cactus type make a strong outline when drawn, and the bud beside the open bloom shows what's still to come. It's the dahlia at its showiest.