From fluorescent dahlias to yellow-and-red cannas, turn on to bright summer colours

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I sometimes do a very bad thing, which I am a bit scared to admit: I buy bulbs then never get around to planting them. My heart has sunk a few times now as I pull a strangely familiar plastic bag from under a chair and realise that it contains the half-sprouting, still-optimistic remains of three packets of tulips.

Summer bulbs are even easier to lose off the radar than spring ones – at least all you have to do with spring bulbs such as daffodils is tip them into a hole. As they're no effort, I tend to do it straight away – and when they're in, you can leave them be.

Summer-flowering bulbs, on the other hand, are mostly brightly coloured plants from far-flung parts of the world, such as begonias and dahlias, and they require real care and attention to get going. They have soft foliage that is delicious to snails, and can't be planted outside until the risk of them getting a cold night's frosting has totally passed.

Why do I keep buying them? Well, the big reason to grow any bulb is that their impact is almost assured (just as long as you don't leave them in the bag under a chair). Unlike herbaceous plants, which grow from a set of roots, a bulb carries almost everything it needs to get going in-house. If you can manage to dampen it with water every now and again, the bulb will do all the rest ofthe work for you.

Start with cannas. Technically, they're rhizomes – open the bag, and among the earth you'll find something that looks like a dried-up bit of ginger from the bottom of your fridge. But plant them in some good compost and they will produce big tropical leaves to add a touch of satisfying jungliness to your garden.

There are some good canna flowers, too – this year I am planting some Canna "Picasso" which I spotted last year at Wisley. Its spatter-patterned flowers in yellow and red are more reminiscent of a flea-market scarf than a Picasso, but in the RHS garden they added a strong touch of exotic zinginess, ratcheting up the planting's whole effect at least a notch. Let's see if they can do the same for my front patch.

I am not particularly good with dahlias, but I still keep trying. This year, my dahlias – which the Aztecs used for food and religious ceremonies – are going to start off inside in pots, and aren't going outside until they've grown far too big to be eaten overnight by slugs (their usual fate). I have gone for the practically fluorescent "Bora Bora".

Lastly, what about something for people trying to exhibit some taste? Well, the word in gardening circles is to go for Gladiolus callianthus, a gorgeous plant that comes from the wilds of Ethiopia and Somalia, whose white, star-shaped flowers will exude an amazing fragrance on late summer's evenings. Happy planting.

Three to plant: Brighten up your outlook

Eucomis bicolor

The South African pineapple flower, a gorgeous long-flowering mixture of burgundy and green (five for £4.95,

Galtonia viridiflora

A super-stylish waterfall of greeny-white flowers from South Africa (three for £4.30,

Cautleya spicata

A member of the ginger family from the Himalayas, with red and yellow trumpets (£3.75 per clump,