A floriferous and bountiful window box can stop passers-by in their tracks, elevate the visual appeal of your home and say ‘welcome’ to visitors.
But creating one with longevity and interest can feel a bit daunting – I’ve certainly had moments of panic in the garden centre, desperately rearranging the contents of my trolley, checking labels for flowering times and worrying that my window box will end up an uninspiring mound of dated bedding plants, or else become a dead, crispy brown mess within weeks.
Luckily, I have experts galore to turn to, and with their help I’m mastering the art of an on-trend and well-crafted window box.
Pick plants for pollinators and people
“With the world as it is, window boxes should include plants that are great for biodiversity, as well as looking good for months,” says the queen of gardening, author and podcaster Sarah Raven.
The trick, she tells me, is to select plants pollinators love, but that are also edible (for us) and that look good in the vase. “You’ll be on to a triple winner – good for the planet, good for decorating the house inside and out, and good for the kitchen,” she says.
Easier said than done when there are literally hundreds of plants to choose from, so here’s an easy cheat courtesy of Sarah: “My current favourite combination for window boxes is to use pollinator-friendly, scented-leaf pelargoniums such as ‘Prince of Orange’ or ‘Attar of Roses’, which have the most delicious rosy fragrance. I use the leaves for cordials and the flowers are edible, and they last an incredible 3–4 weeks in a vase.
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“Then add in sages like Salvia viridis ‘Blue Monday’, along with rosemary. Rosemary prostratus has fantastic cascading, evergreen foliage, and ‘Tuscan Blue’ has deep blue flowers in spring and summer and sometimes flowers again in autumn.”
Sarah reassures me you don’t need a mansion-sized windowsill for all this. “You can put them in one large window box or plant them in a succession of boxes on different sills. Just make sure they’re on the sunny side of your house.”
Embrace the dark side
One trend I’ve definitely embraced is giving those overlooked, shadowy bits some green love. I’ve learned a lot from Susanna Grant, author of handbook Shade and founder of specialist shade-plant consultancy Linda.
“Shady sills are actually better for window boxes than sunny ones,” she explains. “They are slower to dry out, easier to keep watered and can be filled with plants that look good all year. I’ve seen more ferny green window boxes popping up everywhere, and it really makes a difference to the front and inside of a house.”
Susanna is brilliant at seeing shade as an opportunity for lush planting. “My tip is to treat a window box like a miniature garden with an evergreen or two, a couple of perennials that flower at different times and some spring bulbs for when it’s looking a bit bare.”
I’m in love with the window box at her home, so ask her what’s in that. “It’s on an east-facing sill,” she says, “and has two contrasting ferns, Korean rock fern and Japanese shield fern, valerian and Scots lovage for height, muscari ‘Valerie Finnis’ and anemone blanda for colour, and a hellebore for early spring interest.”
Make it edible
“The trend I’m seeing is that people are wising up to the fact that window boxes can be useful as well as beautiful,” says kitchen gardener Anna Greenland, who has grown edibles for chefs including Jamie Oliver and Raymond Blanc and has packed much of her wisdom on container gardening into her book Grow Easy.
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She agrees with Sarah Raven that there’s a trend towards thinking about pollinators as well as ourselves: “Window boxes don’t need to be just bedding plants. Filling them with a mix of colourful vegetables, herbs and edible flowers is a win for you and the pollinators.
Leafy greens like chard, dwarf kale and salad leaves work well, as do dwarf runner and French beans or tumbling tomatoes. Add in calendula, French marigolds, violas and trailing nasturtiums for salads and allow herbs like basil, chives, parsley, rosemary, sage and thyme to flower and lure in beneficial insects and bees.”
She’s got just the recipe for anyone looking for a list to follow. In one sizeable 1m box, include the following: 2 calendula plants, 3 chard ‘Flamingo’ and/or rainbow chard, 2 dwarf runner bean ‘Hestia’ and 1 nasturtium ‘Black Velvet’.
Matthew Biggs’s Guide to Planting a Window Box
The pro gardener and Gardeners’ Question Time regular shares his top tips for creating a window box with staying power
Prepare your vessel
Choose a window box that is as deep and wide as the space allows to ensure your plants have room to develop a good root system. Make sure there are sufficient drainage holes then put a crock (broken piece of terracotta pot) over each hole to avoid compost washing out. Raise the window box on pot feet or blocks of wood to improve drainage.
Use peat-free multipurpose compost with added John Innes compost for better water retention. To find out if your window box needs watering, push your index finger down into the compost and pull it out. If there are fragments of compost on your finger, it is still damp enough, if not, water thoroughly. A good, thorough soaking every few days is better than a little sprinkle every day.
Feed and deadhead
Feed the plants with a general fertiliser until they are established (growing strong), then change to high potash fertiliser (such as tomato feed) for strong flowering. Remove dead flowerheads from plants like petunias, violas and wallflowers to encourage a second flush.
GH LIVE – Join our Good Gardening talk on Friday 24th June and have your horticultural questions answered by our expert panel including RHS Chelsea gold-medal winner Juliet Sargeant, regular BBC Radio 4 Gardeners’ Question Time panellist Bunny Guinness, and gardening journalist Pattie Barron. More about this event and tickets here.