I'm not a great one for garden gizmos as most fail to live up to expectations, but one I would recommend is Flower Pouches.
You can pick them up on Ebay for a couple of pounds, buy a tray of bizzy lizzies in B&Q for a similar amount, plant them out, hang them up and they'll flower until the first frosts. Just rememebr to water them, daily in warm weather, and feed them once a week.
I've just planted mine and put them at the front of the house. At the moment they look like this.....
I know you can see lots of the plastic bag, but if you feed and water as above within a few weeks they'll look like this (photo from last summer).