Continue to sow seeds of annuals, in gaps in borders, or in containers. And don't forget the headily-fragrant, night-scented stock: it is traditional to sow this modest-looking, grey-lavender-flowered plant along with Virginia stock which looks roughly similar, although much brighter. This year, Unwins Seeds have introduced a new night-scented stock, `Starlight Scentsation' a mixture of lively colours, which may be worth trying.
Meanwhile, if you have a greenhouse, you can start potting up containers of frost-tender plants, including pelargoniums (tender geraniums), verbena, lobelia, begonias and petunias. When all risk of frost is gone, these can be placed outside in strategic positions to brighten up tired corners, or to add a bit of gaiety around doors, windows and patios. If you use terracotta pots, soak them in water for a couple of hours before planting. They will absorb a lot of water which will slow down the speed at which the compost dries out. In very hot weather, this trick helps keep the roots cool.