Window boxes are a great option to add masses of colour, adding so much interest at your eye-line.
Because they’re at a height that’s midway between your pots and hanging baskets, you can get a ‘hanging garden’ effect with tiers of lush hanging plants. They also have a pretty framing effect around the window, which can be seen from both indoors and out.
There are some trickier practicalities to deal with, which is why you don’t see them as often as hanging baskets. But don’t be put off, as there are containers and kits on the market that make having a window box easier than ever.
If you have a stone windowsill you can sit containers directly on top and drill through the base to attach them securely.
However, if you have uPVC double-glazing you can’t drill directly into the plastic windowsills, so the best approach is to attach supporting brackets to the brickwork under the window.
Many window boxes now come with a frame or brackets that do this job – all you need to do is drill the holes and find appropriate sized rawl plugs. Brackets also help keep the box slightly away from the wall, which is reduces the risk of the wall getting damp.
Safety is important too so make sure the masonry screws you use are long enough to take the weight – at least 5cm long – and there are enough of them.
If you’re using your own supportive brackets, use them every 45cm (18in) underneath the length of the box. A good rule of thumb is to install the brackets as if you were putting up a bookshelf for encyclopaedias!
When it comes to planting, opt for trailing plants such as Glechoma hederacea 'Variegata' (trailing nepeta) mixed in with free flowering bedding such as calibrachoa.
Window boxes are narrow and long in shape and dry out easily, so make sure you can access them easily to water the plants. Many pre-made window boxes now come with self-watering systems – typically a suspended tray with a reservoir of water underneath.
If you are using one of these put some crocks or gravel over the drainage channels and holes to stop them getting clogged up with compost. Use a lightweight potting compost – avoid loam-based composts, which are heavier – and mix in perlite to reduce the weight further.
If you have a railing or fence right outside your window you can use even simpler alternatives, such as horseshoe shaped containers that sit astride the rail or a widow box with a hooked frame – both types are made by container firm Elho and sold at larger garden centres.
GN’s favourite window box plants
Lysimachia nummularia ‘Aurea’ – Also known as golden creeping Jenny, this zesty-green perennial can be used year-in, year-out in a shady position.
Pelargoniums – For masses of blousy colour in a sunny spot opt for a mix of upright and trailing pelargoniums. Deadhead regularly for continual blooms.
Bacopa – Dainty white flowers make this trailing plant work in either a pretty cottage garden window box or a stylish white and green arrangement.