Summer is the brightest time for window boxes: they are drenched in colour from when spring displays fade to the onset of frosts in autumn.
The plants are susceptible to damage from low temperatures and therefore cannot be put outside until all risk of frost has passed. However, when plants are grown in an inner box, they can be planted slightly earlier and at night placed in a greenhouse or conservatory.
During daytime, place them outdoors on a warm, wind-sheltered patio. This way, troughs packed with colour can be ready for putting into a window box as soon as the spring-flowering display fades.
There are many plants that can be used in summer displays, in medleys of colours that are sure to attract attention. Plant them in an inner trough; as soon as the spring display is over, replace it with a summer one, but not until all risk of frost has passed.
PLANTS TO CONSIDER
Anagallis linifolia ‘Gentian Blue’
Growing 15-23 cm/6-9 in high with a sprawling nature, it develops masses of 12-18 mm/1/2-3/4 in-wide, rich blue flowers with bright centres form early to late summer. Plant it where the stems can spread and trail over the container’s edges. It colour contrasts with Sweet Alyssum (Alyssum maritimum/Lobularia maritima) along the fronts of window-boxes and crates an eye-catching display throughout summer.
Asparagus densiflorus ‘Sprengeri’ (Emerald Fern)
A superb cascading foliage plant that is ideal for crating backgrounds for smaller plants. It has long, arching, wiry stems packed with green, needle-like leaves.
Coleus blumei (Flame Nettle)
A tender foliage plant widely grown indoors during summer. In warm areas it is also ideal in window-boxes and troughs. Most varieties are upright and bushy, but some have a trailing nature and are ideal for planting at the fronts and sides of window boxes.
Trailing types include ‘Scarlet Poncho’ and ‘Molten Lava’. Both of these can be raised from seeds which should be sown in gentle warmth in late winter or early spring.
Conifers (miniature and slow-growing types)
These are mainly used to crate colour in winter and spring displays in window-boxes, but they can also be used in summer arrangements. They are especially useful in exposed and cold areas, as they help to give protection to annual plants.
Fuchsias are popular summer-flowering plants for window boxes. Although some species are relatively hardy and can be planted in borders in temperature climates, the majority are soon damaged by low temperatures and therefore cannot be put outside until all frosts has ceased.
Some varieties have a cascading nature that soon drenches the sides of window boxes with colour, while others are bushy. Both have a role to play: trailing types at the ends of window boxes, bushy ones towards the centre. Avoid varieties with a stiffly upright stance; rather, select those with a lax nature such as ‘Lena’ (semi-double, pink and magenta) and ‘Swingtime’ (double, red and milky-white).
Trailing types (also suitable for growing in hanging baskets) include ‘Cascade’, ‘Jack Acland’, ‘La Campanella’ and ‘Walsingham’.
It is possible to plant a windowbox entirely with fuchsias, but companionable plants include Zonal Geraniums (pelargoniums), marigolds, salvias and begonias.
Glechoma hederacea ‘Variegata’ (Variegated Ground Ivy’)
Creates a mass of mid-green, kidney shaped leaves with white markings, in bushy clusters at the plant’s top and then clustered around long, trailing stems. It is ideal at the fronts and sides of window boxes, as it cloaks them in leaves without creating a high, dome-shaped top that obscures plants at the back.
As a bonus, it has lilace-blue flowers during late spring and early summer.
Hedera helix (Ivy)
There are many small-leaved, variegated varieties that can be used to trail from around the edges of all types of window boxes.
Select the leaf colours to suit the colour vibrancy of the display. For example, if the window box is bursting with exceptionally bright colours, the ivies can be garish. But when the colours are demure and reserved, ensure that the ivies do not dominate the display. Indeed, these trailing plants should be secondary features, just clothing the sides of window boxes and softening their outlines.
CALCEOLARIA X HERBEOHYBRIDA (Slipper Flower)
Height 20-30 cm/8-12 in, plant 20-25 cm/8-10 in apart. It is often grown as a house plant; outdoors it flowers during early and mid-summer , bearing bright, pouch-like flowers.
BRACHYCOMBE IBERIDIFOLIA ‘Splendour’ (Swan River Daisy)
Height 23-30 cm /9-12 in, plant 15-20 cm/6-8 in apart. Each plant creates a mass of large , daisy-like flowers in blue to purple or white with ebony eyes.
CAMPANULA CARPATICA ‘Bellissimo’
Height 15 cm/6 in, then, trailing plant 20-23 cm/8-9 in apart. Position at the sides and fronts of boxes, so that it covers edges with chalice-shaped, blue or white flowers throughout summer.
CAMPANULA ISOPHYLLA (Star of Bethlehem):
Height 15 cm/6 in, then trailing, plant 20 cm/8 in apart. Superb trailing plant with masses of blue flowers from mid to late summer. There is also an attractive white-flowered form that looks good against a red wall.
Height 10-15 cm/4-6 in, then trailing, plant 20-23 cm/8-9 in apart. It develops masses of rose, lemon, pink and white, trumpet-shaped flowers from mid to late summer. Plant at the fronts and sides.
Height 20-30 cm/8-12 in, plant 15-23 cm/6-9 in apart. It creates neat mounds of flowers, in blue or mixed colours, from early to late summer. Do not use tall varieties.
Are a large and varied family, many ideal for growing in containers on patios, including window boxes.
- The tuberous-rooted Begonia x tuberhybrida is dramatic and dominant in window boxes, with single or double flowers often 13cm/5in or wider, from early to late summer. Flower colours include yellow, pink, red and scarlet.
- They are usually grown from dormant tubers planted in boxes of moist peat in early spring, and later transferred to separate pots when shoots appear.
- After all the frosts have gone they are planted into window boxes and other containers outdoors. The Basket Begonia (Begonia x tuberhybrida Pendula’) is a trailing form, widely used in hanging baskets and at the side of window boxes.
- The fibrous-rooted Wax Begonia (Begonia semperflorens) is as much at home in displays indoors as in flower borders outdoors. Also, it is supreme in window boxes. It forms bushy plants, 15-23cm/6-9in high and wide, with masses of red, pink or white flowers from early to late summer.
- Wax begonias are easily raised from seeds sown on the surface of compost in late winter or early spring in 16C/61F. Germination takes two to four weeks and when the seedlings are large enough to handle they are pricked out individually, or in small clusters, into seed-trays. Harden off the plants and put them outdoors when all risk of frost has passed.
- Nip out the growing tips of plants several times to encourage them to be much bushier.