They'll bring a riot of colour to your garden that'll last right through to the final days of autumn

The stories of the plants we grow are as fascinating as the plants themselves. Their histories, the tales of how they reached our shores; the great majority of the plants we grow in our beds and borders, not to mention the crops we cultivate, are from other parts of the world.

Most of the time it’s obvious that neither they nor their ancestors ever graced our hedgerows or fields. They’re far too exotic and alien, yet that doesn’t stop us from bringing them into our gardens, probably alongside other plants from entirely different locations and combining them to paint beautiful pictures.

A few weeks ago in our polytunnel the first of our dahlias started to flower. Several plants simultaneously opened, single and bright red with a hint of darkness about their foliage. These were all grown from seed given to me at Cambridge Botanic Gardens, collected from a veteran plant of Dahlia coccinea that grows just outside one of the greenhouses there and presumably is never lifted. First recorded in drawings from Mexico in the 16th century and as being grown in Europe in the first years of the 19th, what a thrill it must have been to discover these strange and exotic flowers.

Spanish and Portuguese hidalgos in Mexico during the early 16th century were charged with studying crops, food and medicines. Dahlia tubers were eaten, used medicinally and the hollow stems of D. imperialis were even used in plumbing!

It wasn’t until much later that gardeners discovered the horticultural value of the dahlia, with hybridists eventually getting to work to produce the forerunners of the vast array available today.

So many of our plants reached us in the search for food and a few the other way around. Runner beans were introduced originally from Central America for their ornamental value. Many gardeners in the USA grow them to attract their pollinators – hummingbirds. They’re in short supply in the UK; we rely on bees.

South and Central America are the source of some of our most exciting food, from chillies to chocolate. In common with many Central and South American plants, dahlias were introduced as possible food. Potatoes were also tubers and perhaps it was thought that dahlias might have been as popular as spuds! Dahlia chips anyone?

Because we grow a lot of single dahlias at Glebe Cottage, many of them set seed without any intervention from us and each year we sow a small quantity of the collected seed. We sow it the next spring, it germinates rapidly and seedlings are potted on.

By the end of summer each plant has formed several tubers. Kept frost-free through winter, they can be brought into growth with the older dahlias in the spring. All the young plants from last year have been potted on and a few have already flowered.

Dahlia seed is fascinating and it’s worth having a go yourself, but even if you make no attempt to cross-pollinate plants and just collect the seed it’s an enjoyable and often rewarding exercise. Placing the whole seed head in a paper bag and keeping it in a dry but cool place soon loosens the seed. Store in a paper bag until next spring, but take a look at the little platform where those seeds were attached. They leave behind a fascinating spiral pattern – conforming to the Fibonacci sequence.

Enough about maths and history, it’s time to get our dahlias out into the garden where they’ll bring a riot of colour through to the last days of autumn.