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A window box can be a whole lot of garden in a very confined space!
Did you know that some container gardening books are dedicated specifically to the rectangular container known as a window box? This is easy to understand, as there is something endearing and heart-warming about a window box spilling colourful flowers, or a window box containing complementing combinations of interesting foliage and textured grasses.
Planting up as many window boxes as you can in autumn is a real joy, as nurseries are filled with cold-season annuals in flower, cooking herbs, pretty ornamental grasses and the cutest succulents. And remember: a window box does not necessarily need a window as a backdrop. Custom-made window boxes can be fitted to balcony railings or simply displayed in a row on a patio floor. You can also fit a trellis panel to a large window box and include a dainty creeper into your planting recipe. The result can be a form of vertical gardening against a wall or a ‘room divider’.
Consider The Mechanics
- If the windowsills are too narrow to accommodate a box, attach strong brackets to the wall beneath the window to give them more support, keeping in mind that the windows might open sideways, which will confine you to using only low-growing, cascading plants.
- To avoid muddy dribbles, line window boxes with disposable kitchen cloths or weed-control fabric to allow drainage, but prevent the soil from washing out.
- Drip trays for window boxes can be used to prevent a mess but must be filled with gravel before positioning the window box (which must have drainage holes at the bottom). The container filled with plants should never stand in water accumulated in the drip tray – they will rot and die off.
- Window boxes must be very securely fitted to a balcony railing to stop them from falling onto the head of a passer-by. Also, think about watering and a muddy stream of water that might run from your balcony to the ground below. A better option would be to buy a window box fitted with a built-in drip tray.
- Use a lightweight commercial potting soil. If weight is a worry when large window boxes are planted up, the potting soil can be bulked up with lightweight materials such as perlite, peat or vermiculite – ask your local nurserymen for advice.
How to Plant a Window Box
First place a lining of water-permeable fabric over the drainage holes in the window box, then add a layer of potting soil. Arrange the plants, still in their nursery containers, until you are satisfied with a composition that pleases your eye. Turn them out of their nursery containers, loosen the roots gently and put them in place, while filling up around them with more potting medium. Fill up the window box to about 2cm below the rim of the box to allow room for watering. If there are large gaps between the plants you have chosen, fill them with instant colour in the form of annuals or low-growing groundcovers with contrasting foliage colours, which are always available in trays.
Try ‘Trick Planting’
You can ‘plant’ seasonal flowering plants without removing them from their nursery pots and fill in the spaces between them with bark nuggets – the hassle-free way to change the look of your window boxes seasonally without having to dismantle anything.
- It’s not too late to plant some cheerful yellow daffodils teamed up with dainty Primula malacoides in a mix of white and soft lilac – an uncomplicated combination for a window box that receives morning sun and afternoon shade.
- Wintertime is pansy and viola time, and seedling tables will be filled with trays of these plants, already in full flower – their happy flower faces are made for window boxes in full sun or semi-shade.
- Modern petunias, like the cascading Supertunias or the many hybrids of the petunia-like Calibrachoa, with its sprawling habit and an abundance of small flowers, are fantastic for sunny winter boxes in summer-rainfall areas.
- Ask for Osteospermum (Cape Daisy) – there are many varieties in a wide range of colours that will create a fantastic display in a sunny window box. They flower from late winter and well into spring. Other indigenous plants like Nemesia ‘Nesia’ and diascias are equally spectacular!
- If shade is a problem, plant your window box full of bronze- or green-leaved waxy begonias. The flower colours range from pure white, two-tone pink and white to bright pink and post-box red. These annuals or biannuals are value for money as they flower for months on end!
- For fresh salad greens ‘on tap’, combine different pick-a-leaf-and-come-again salad varieties in a sunny window box.
- If you just need some basic fresh herbs, plant chives, parsley, thyme and rosemary together. The window box will need some sun occasionally, but will also flourish at a window on the southern side of a building.
- Pack compact evergreens like Euonymus japonicus ‘Microphyllus Gold Dust’ or dwarf Coprosma hybrids like ‘Pacific Sunrise’ tightly together in a large window box for gorgeous winter foliage.
- Spreading groundcover conifers like Juniperus horizontalis ‘Prince of Wales’ have a calming effect with their coarse but beautiful foliage textures and spreading growth habits. They are extremely winter-tough if there is enough sun to keep them happy.
A window box is a confined space imprisoning plant roots and keeping them from seeking moisture and nutrients on a wider front, such as in open garden soil.
- Never allow any plant combination to dry out completely. Water every day if the top soil layer feels dry to the touch.
- Ask at your local nursery about water-retaining products and how to use them at your local nursery. In densely planted containers they can go a long way to keeping your window box garden alive.
- Invest in a water-soluble foliar fertiliser and feed your plants at least once a month.
- Dead-head flowering plants to encourage more flowers, and if you have anything ready to harvest for eating or cooking, don’t be shy to do it.