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Growing giant sunflowers – planting out

Last month, we challenged you to break the World Record for growing the tallest sunflower. Free seeds of 'Russian Giant' were given out with the April issue of Gardeners' World magazine, and many of youemailed us to register your interest in taking part. We allsowed our seeds, watered, tended and waited.

Now, in late May, we should all have good, strong sunflowers, ready to plant out (depending on where we live). Mine have been outside in pots for about three weeks now, but I only planted them in their final positions last weekend. They're roughly 50cm tall and healthy looking, but they're not as tall as Adam Pasco's greenhouse-grown ones. Obviously they'll catch up and take over his soon.

All but one of the sunflowers are planted in well-rotted compost at the back of my south-facing border, close to the wall where they'll be kept warm at night. As an experiment, one is planted in a bucket of semi-rotted compost, like a portable bean trench. All are staked with tall, strong bamboo canes. (They're only about 2m tall, though. I'm still not sure how I'll stake an 8m tall plant.)

I haven't done anything special with my sunflowers yet, I've only watered them. Now I'm upping my game: this weekend I'll be harvesting nettles to make a nitrogen-rich feed, which I'll use regularly when I water the plants. Nitrogen-rich feeds, which include chicken and horse manure, encourage leafy growth and height, as opposed to flowers. I'll avoid using potash-rich fertiliser (such as a comfrey, or tomato feed) for now, as that will encourage flowering, diverting the plant's energy and reducing its height. A potash-rich feed will come in handy when the plants are tall, however, as it will help strengthen the stems, which is essential when growing plants to such heights.

It's all very exciting. I find myself inspecting the sunflowers more than any other plant in my garden – checking for unwanted flower heads and ensuring they're well tied to their stakes. I'm anticipating a growth spurt any day now.