Whether you have a sunny window on the 10th floor or a shady basement view, windowboxes are a great way to add interest and colour to the outside of a building. Plants can be chosen to suit the situation and can be changed through the seasons or planted once for year-round interest.
Decorative appeal
Windowboxes these days are often overlooked, but can be an enjoyable aspect of container gardening that offers a wide range of opportunities for ‘dressing up’ both the front and back of a house. Choosing the same type of container and planting combined with the same colours and cultivars immediately brings a sense of cohesion and a strong overall colour scheme, particularly if teamed with similar plantings in hanging baskets or pots on the ground (left).
For year-round appeal, windowboxes can be planted up with evergreens, but many gardeners prefer to ring the changes with temporary seasonal plantings providing maximum colour.
Planting schemes do not have to be based entirely on flowers: teaming a selection of plants with contrasting foliage shapes, colours and textures can be just as effective as blooms.
Permanent plantings
Use a loam-based compost such as John Innes No 2 for permanent plantings. For all-season colour include a mixture of compact evergreens such as Hebe pinguifolia ‘Pagei’, Euonymus fortunei ‘Silver Queen’, Berberis buxifolia ‘Pygmaea’ and Artemisia schmidtiana ‘Nana’. Dwarf conifers can be especially useful - consider Chamaecyparis pisifera ‘Nana’ or Juniperus communis ‘Compressa’. For a shady window try combining Helleborus niger (Christmas rose), trailing ivy and Vinca minor.
Changing the palette
If you prefer to refresh your windowboxes with seasonal planting, multipurpose or peat-free compost can be used. It would be advisable to incorporate extra grit for succulent and subtropical plantings.
To make colour last through winter into spring, plant a mix of winter-flowering pansies and heathers, wallflowers, polyanthus and large-flowered cultivars of Bellis perennis (bedding daisies). Beneath these, pop in a few miniature spring-flowering bulbs such as Muscari (grape hyacinth), Iris reticulata cultivars, dwarf tulips or dwarf daffodils such as Narcissus ‘Tête-à-Tête’.
Planting position
The choice of summer bedding is wider, but tailor your selections to aspect. Sun lovers such as gazania, petunia, tagetes and Limnathes douglasii will revel in south-facing windowboxes, providing they receive adequate water - sometimes watering twice a day may be necessary. For shadier aspects there are Begonia Semperflorens Cultorum Group cultivars, the many selections of busy Lizzies available, fuschia or nemesia, all of which will produce plenty of flowers, even in fairly low light levels. From a wide choice of trailing plants on offer try cheery nasturtiums, a cooling silver cascade of Helichrysum petiolare or, for a dark wall, Lysimachia nummularia ‘Aurea’ (golden creeping Jenny).
Watering
Windowboxes can quickly dry out during sunny or windy weather and may need watering more than once a day during summer. A light mulch can be added to retain further moisture.
It can be well worth investing in a drip irrigation kit. Buy one with a timer if you are likely to be away from home for long spells. Alternatively, incorporate water-retaining gel crystals in the compost. Be careful not to overwater in winter, however, as the compost may freeze and damage the plants.
Adding fertiliser
From spring to summer, when plants are growing rapidly, apply a well-balanced liquid fertiliser once a fortnight or use controlled-release fertiliser pellets mixed with the compost to provide a steady release of nutrients throughout the year.
If seasonal plants begin to flag, tidy them up by removing dead leaves and flowers, and use a high-nitrogen liquid feed to stimulate fresh growth. Perennial plants may need dividing every couple of years; alternatively, remove and transplant into the garden if they begin to outgrow their space.
Choice of container
Many styles of container are available and each will display your plantings differently. A metal planter will give a modern edge while wood and natural materials such as terracotta give a more traditional effect. Although planters are readily available, windowboxes are easy to make using treated softwood, hardwood or marine ply.
To prevent the compost drying too quickly ensure the box is at least 20cm (8in) wide and 15cm (6in) deep. Several drainage holes should be drilled in the bottom, with broken crocks or gravel added to encourage free drainage.
A box that runs the full length of a window will look better and be less prone to drying than shorter boxes.
Wall planting
Windowboxes and other wall containers need to be securely mounted to ensure they are safe. Boxes can simply be screw-fixed onto wide sills but be sure the window can still be opened. Alternatively, secure the box to the wall beneath the sill using screws and wall-plugs, ideally with metal brackets underneath for support.
Troughs and windowboxes need not be
limited to use on windowsills alone. Providing they are well secured - on trellis or wire netting (left) - they can be fixed to walls, allowing their content to cascade and trail down , or placed on the ground in front of supports and used to grow climbing plants.
When fixing containers to a wall, stout wire mesh can be used to cover the wall, attached firmly to battens with staples and pots and planters can be hung anywhere on this (right).
Vertical kitchen gardens
For gardeners with limited space, or with restricted use of soil in the case of paved gardens and yards, container gardening is particularly valuable and its techniques are as applicable.
Foliage and flowers of edible crops can be attractive in their own right, providing a
year-round harvest right outside the kitchen window. A surprisingly wide range of crops
can be grown in this way on a sunny wall including aubergines, chillies, cucumbers,
cherry tomatoes and cut-and-come-again salad crops such as lettuce and rocket.
Even alleyways, buildings and garden walls can be used as innovative planting spaces, vertical growing providing convenience of height, water supply and access to power supplies.
Helen Bostock