Blimey, Dave, you can buy wild rocket seeds for 50p or a quid almost everywhere! They don't need anything special, but give 'em a decent patch or two of bare soil to begin with and just chuck the seeds in. They'll grow among your flowers though they'll look a tad weedy. I don't grow anything to eat where I'm using artificial fertilisers or weedkillers or insecticides. The plants bolt quite easily but you can still use the shoots as long as they haven't gone too far. The only problem I've ever had is flea beetle, which eats tiny, neat holes in the leaves. An aesthetic issue only, and you'll still get plenty of unaffected leaves. They are jolly plants that seed themselves freely.