SUNFLOWERS are the world's tallest single stem flowers and this year the Guardian, in conjunction with Weaver Vale Garden Centre, is offering a prize to the person who grows the tallest one.

Capable of reaching a staggering three metres in height and growing at a rate of about 30cm a week, sunflowers are valuable for forming a background screen in gardens.

But for gardeners who worry the giant plant might prove too much competition for neighbouring flowers, dwarf sunflowers make popular bedding plants.

Sunflowers grow best when grown on soils with adequate water-holding capacity, internal drainage and proper fertility.

They can cope with a wide range of soil types but one that is too high in nitrogen encourages excessive plant growth that will stunt the maturity of the flower head.

Clare Swatridge, group plants manager at Weaver Vale said: "It's best to give sunflowers a lot of water, a sunny position and some support because although the stems are strong, as they get taller someone only needs to bump into it for it to break."

She also recommends watering them in the evening or early morning, when the sun is not strong and likely to cause evaporation.

Harvesting begins in mid-September and can run into October. A check of the flower head will indicate maturity - florets in the centre of the flower disc shrivel, the head flops down and it turns a lemon yellow colour on the back.

The closing date for the Guardian competition is Friday, September 19. The winner will receive a £10 gift voucher from Weaver Vale. To enter simply let us know when you think your sunflower has reached its peak and we will come along and photograph the most likely contenders. You will need to be able to prove the height of your prize bloom.

Weaver Vale Garden Centre is on Winnington Avenue, Northwich.

ecummins@guardiangrp.co.uk