When it comes to adding a touch of charm and beauty to your home, few things rival the simple elegance of a well-designed window box. Whether adorning a townhouse in London or a cottage in the countryside, a window box bursting with colourful blooms is a delightful sight to behold.

However, creating a window box that thrives under the ever unpredictable British summer requires careful consideration of plant selection. In this guide, we’ll explore how to design a window box for full sun, incorporating vibrant blooms and statement centrepiece plants commonly found in the UK.

Selecting the Right Plants

In the context of gardening, the terms “thriller,” “spiller,” and “filler” are often used to describe different types of plants based on their growth habits and roles within a container arrangement like a window box. Here are some popular choices that are well-suited to UK weather conditions:

1- Thriller Plants

Thriller plants serve as the focal point or centrepiece that commands attention and adds height and drama to the display. These plants are typically tall or upright in growth habit, standing prominently above the other plants in the arrangement. Here’s a closer look at some common types of thriller plants, along with their characteristics:

1. Salvia: Salvia, also known as sage, is a versatile and popular choice for thriller plants in container gardens. With its tall spikes of flowers in shades of blue, purple, red, or white, salvia adds vertical interest and attracts pollinators like bees and butterflies. It’s a drought-tolerant plant that thrives in full sun and well-drained soil.
2. Ornamental Grasses: Ornamental grasses come in a variety of shapes, sizes, and textures, making them excellent choices for thriller plants. Tall grasses like Pennisetum (Fountain Grass) or Miscanthus provide graceful movement and architectural interest with their feathery plumes or elegant foliage. They can add a sense of movement and drama to the container arrangement.
3. Dracaena: Dracaena is a striking tropical plant that works well as a thriller in container gardens, particularly in larger pots or planters. Its tall, sword-shaped leaves come in various shades of green, yellow, or variegated patterns, adding a bold and exotic touch to the display. Dracaena thrives in bright, indirect light and prefers well-draining soil.
4. Cordyline: Cordyline, also known as Ti plant, is another tropical thriller plant prized for its dramatic foliage and vibrant colours. With its long, sword-shaped leaves in shades of green, red, pink, or burgundy, cordyline adds a tropical flair to container arrangements. It’s relatively low-maintenance and thrives in full sun to partial shade.
5. Agapanthus: Agapanthus, commonly known as Lily of the Nile, is a perennial plant that produces tall stalks topped with clusters of trumpet-shaped flowers in shades of blue, purple, or white. Its architectural form and striking blooms make it an excellent choice for a thriller plant, particularly in coastal or Mediterranean-style gardens. Agapanthus prefers full sun and well-drained soil.

2- Filler Plants

Filler plants are an essential component of container gardening arrangements, providing volume, texture, and color to complement the thriller and spiller plants. These medium-sized plants fill in the spaces between the taller thriller plants and the trailing spiller plants, creating a cohesive and balanced display. Here’s a closer look at some common types of filler plants:

1. Geraniums (Pelargoniums): These classic summer flowers come in a variety of vibrant hues, including red, pink, and white. Geraniums are drought-tolerant and bloom profusely throughout the summer months, making them a classic and safe choice for window boxes.
2. Petunias: With their trumpet-shaped flowers in shades of purple, pink, and white, petunias add a splash of colour to any window box. They are heat-tolerant and bloom continuously, providing a beautiful backdrop for other plants.
3. Lobelias: These delicate trailing plants produce masses of tiny flowers in shades of blue, purple, and white. Lobelias are perfect for adding a cascading effect to your window box and can tolerate full sun with adequate moisture.
4. Verbena: Known for its clusters of small, brightly coloured flowers, verbena is a popular choice for summer containers. It thrives in hot, sunny conditions and attracts butterflies and bees to the garden.
   Choose a Verbena ‘Union Jack Mixed’ for a patriotic mix of red, white and blue-purple blooms held on slender stems above dark green foliage.
5. Calibrachoas (Million Bells): Resembling miniature petunias, calibrachoas are prolific bloomers that come in a wide range of colours, including yellow, orange, and magenta. They are drought-tolerant and ideal for adding a pop of colour to your window box.

3- Spiller Plants

Spiller plants soften the edges of the container and creates a sense of lushness and abundance. These plants spill over the sides of the container, creating a graceful and flowing effect that enhances the overall aesthetic appeal of the arrangement. Here’s a few of my favourites:

1. Nasturtium (Tropaeolum majus): Nasturtiums are annual flowers prized for their edible flowers and leaves, as well as their trailing growth habit. They come in a variety of colors, including vibrant oranges, yellows, and reds, and their trailing stems make them perfect for hanging baskets and container gardens. Nasturtiums prefer full sun and well-drained soil.
2. Sweet Potato Vine (Ipomoea batatas): Sweet potato vine is a popular choice for adding a splash of vibrant color to container arrangements. Its heart-shaped leaves come in shades of chartreuse, purple, and variegated patterns, creating a striking contrast against other plants. Sweet potato vine trails gracefully over the edges of containers and thrives in full sun to partial shade.
3. Bacopa (Sutera): Bacopa, also known as Sutera, is a versatile trailing plant that produces small, star-shaped flowers in shades of white, blue, and lavender. Its delicate stems spill over the edges of containers, creating a graceful and airy effect. Bacopa blooms profusely throughout the summer and prefers full sun to partial shade and consistently moist soil.
4. Lysimachia ‘Goldilocks’ (Creeping Jenny): This cultivar of Creeping Jenny features vibrant golden-yellow foliage that adds a bright and cheerful touch to container gardens. Its trailing habit makes it ideal for cascading over the edges of pots, providing a stunning contrast against other plants. ‘Goldilocks’ thrives in partial shade to full sun and moist, well-drained soil.
5. Silver Falls (Dichondra argentea): Silver Falls is a striking trailing plant with cascading stems covered in small, silver-gray leaves. Its silvery foliage adds a touch of sophistication and elegance to container arrangements, creating a beautiful contrast against brightly colored flowers or other foliage plants. Silver Falls thrives in full sun and well-drained soil, making it perfect for hanging baskets and window boxes.
6. Trailing Black-eyed Susan Vine (Thunbergia alata): Black-eyed Susan vine is a charming annual with heart-shaped leaves and vibrant, trumpet-shaped flowers in shades of yellow, orange, and white. Its trailing habit makes it an excellent choice for spilling over the edges of containers, adding a pop of color and whimsy to the arrangement. Black-eyed Susan vine prefers full sun and well-drained soil, making it ideal for summer container gardens.

Designing Your Window Box

Now that you’ve selected your plants, it’s time to design your window box for maximum impact. Consider incorporating the following elements to create a visually stunning display:

1. Colour Contrasts: Mix and match plants with contrasting colours to create visual interest. For example, pair red geraniums with blue lobelias or purple petunias with yellow calibrachoas for a striking effect.
2. Statement Centrepiece (also called “thriller plants”): Choose a focal point plant to anchor your window box and draw attention. Tall, upright plants like salvia or ornamental grasses can serve as eye-catching centrepieces, adding height and structure to the display.
3. Draping Plants (also called “spiller plants”): Introduce trailing or cascading plants along the edges of the window box to soften the edges and create a sense of lushness. Lobelias, trailing petunias, and bacopa are excellent choices for this purpose.
4. Filler plants: They refers to medium-sized plants that fill in the spaces between the thriller and spiller plants, providing a backdrop of foliage and blooms to enhance the overall aesthetic appeal of the arrangement. Filler plants add volume, texture, and depth to the display.
5. Seasonal Interest: Select plants that will bloom at the same time to ensure a continuous display of colour throughout the summer. Mix early, mid, and late-season bloomers to maintain interest and prolong the flowering period.
6. Weather Resistance: Opt for hardy plants that can withstand the unpredictable weather conditions of the UK, including strong winds and occasional rain showers. Choose varieties that are known for their resilience and durability.

By experimenting with different plant combinations, you can easily create a stunning window box that adds beauty and charm to your home throughout the summer months.