On your marks: The summer Olympians of the plant world are under starter's orders

The Tour de France is over and the Olympics finally under way, so now we can spend the next three weeks gasping, 'She ran it how fast? HOW FAST?' and doing some mental arithmetic about the 20 minutes later we'd have finished.

And the Olympians of the human race have leafy counterparts: an elite group of plants so much bigger, stronger and more spectacular than all others that it's hard to believe they actually arise from the same basic genetic material.

Flowering right now, Crocosmia "Lucifer" makes a scorching display every year; and even in this most disappointing of summers, it is lighting the whole garden on its own. I saw a wonderful stand of it at Heathrow the other day, a blaze of orange across the greyest of skies. "Lucifer" has satanic powers of growth: it's about 1ft taller than other crocosmia and spreads through flower beds with an insouciance suggestive of either terrifying, medal-winning levels of self-belief or behind-the-scenes drug-taking.

Another titan of the August garden is agapanthus, which lifts strong, vivid-blue heads on unfeasibly tall stems to give England a touch of wild Africa. All agapanthus are great garden plants, but just occasionally you meet one that actually makes you stop and stare. And wonder when they last had a randomised blood-doping test. You need to pick exactly the right variety for that jaw-dropping effect, though: try "Northern Star" for a blue giant, "Snow Cloud" for a white.

Red-hot pokers are another sure-fire gong winner, though you need to give them room for a five-star performance, because their strappy leaves do spread out a bit. The bog-standard red-hot poker comes in a violent Tequila Sunrise cocktail-coloured combo of orange bleeding into yellow, but they are more likely to incur gawping if you pick a non-traditional shade. The acid-yellow of "Bees Lemon", and the cycling-vest tones of "Green Jade" are both to be highly recommended. Both trevenacross nurseries.co.uk and burncoose.co.uk have excellent lists for all these plants.

Behind the main contenders should be huge teams working away in support of dramatic spectacle, contributing their own bright colours and sturdy foliage to earn enough points to stay in the game. Setting off August firework colours is simple when you have softer blues to work with, and ceratostigma is a great choice, its substantial mound of foliage studded all late summer with china-blue flowers (£9.99, crocus.co.uk).

Some of the finest of the support plants, though, are the softer lime-green euphorbias, such as E.palustris. This works all summer with anything even slightly orange- or red-toned to produce an internationally recognised level of zing. And E.griffithii "Fireglow" contributes a level of second-tier magic which can only leave you asking, in a Chris Froome-ish way, "Should this plant actually be the leader of the team?" Maybe next year…

Podium placers

Hedychium gardnerianum

A stunning skyscraper of lemon-yellow tiers complete with Norman Foster-ish detailing. Can grow 6ft tall without the use of any performance-aiding substances. Allegedly. £9.95, palmcentre.co.uk

Canna 'Pretoria'

It's no accident that many of these showstoppers evoke South Africa's rich floral heritage, but this one hails from rainy Richmond. £19.99 for a huge plant, palmcentre.co.uk

Caryopteris

'Heavenly Blue' This beautiful, hard-working plant lays a subtle but solid base for any glory-seeking star. £8.99, crocus.co.uk