IF you haven't had time to plant up your window boxes for summer yet, now's the time to plan how to achieve the most dazzling effect.

For me, window boxes should be a riot of colour, a mass of bedding plants mixed with some contrasting foliage which can tumble down and obscure the box while enhancing the look of the outside of your property.

Window boxes are frequently used on balconies to brighten up the urban garden when space is limited and can help bring the garden into the home if the plants are clearly visible from inside.

The containers are usually long and thin, holding relatively little compost, so you'll need to add slow-release fertiliser granules and water-retaining gel to the mix before you start, to help the plants through the summer.

If you have a window that opens outwards, ensure your window box is low enough so that the tops of the mature plants aren't snapped off when you open the window. It may also be worthwhile putting a drip tray underneath the box to stop water dripping down and staining walls unless the drips are wiped away quickly.

But you don't have to have a conventional window box. You can secure a range of individual smaller glazed terracotta containers in a variety of colours along your wall to create a more modern feel, perhaps planting them up with a variety of herbs, especially useful if it's a kitchen window you want to brighten up. The colours you choose for best effect should be based on which way the window box faces - if you have a north-facing box you will be limited to which plants will do well there - and you also need to take into consideration the colour of your backdrop.

Deep purple and red-filled baskets provide vibrant colour in a box on a white-painted wall, while lively yellows and burnt oranges blend in with old stone or brick backgrounds. If your window box is in a sunny spot, you have more choice of annuals. Petunias come in a wide choice of colour, both trailing and upright, and bright colours do well contrasted with the silver grey foliage of Helichrysum petiolare. For variegated ivy, try one of the more delicate variegated types. Pelargonium is one of the most suitable plants as it will survive on windswept high rise balconies where the moisture is quickly sucked out of the soil.

If your window box is in a shady area, busy lizzies will brighten it up, while fuchsias will provide some height, although in my experience fuchsias always need a huge amount of water to do well, so if you don't want to become a slave to the watering can, you may make a different choice.

Dwarf hostas, with their big tropical-looking waxy leaves, can also do well on window boxes in the shade, although you may have to take action if you find a trail of snails climbing up the wall to reach them. They will also need feeding regularly and dividing when the plant becomes too big.

White begonias and geraniums, with a hint of lilac lobelia, make an elegant summer display, while for a more formal effect, clipped box can be livened up with a mixture of verbena, diascia and also ivy-leaf pelargoniums.

If you don't want the bother of changing your window box with the seasons, you can plant the troughs with permanent plants such as Skimmia japonica, dwarf conifers, hebes, dwarf lavender and ivy.