Flower borders were once quite formal and planting them required careful planning and precise placement. This very formalized way of planting annuals is rarely used now except in large public gardens. Nowadays, beds and borders composed solely of annuals are very rare as most gardeners have switched to using perennials with just a few annuals here and there to add splashes of colour after the perennials have waned. Gone too is the practice of having rows of plants with gradually increasing heights. Fewer edging plants are being used and tall plants are now commonly positioned near the front of borders.
It is common to see no short plants in a border at all; all will be of medium height or taller, even those right at the front. Different plants are mixed together in groupings and there are no distinct rows and certainly no one plant is used for the entire length of the border. Instead, a certain plant may be repeated three or four times along the length to establish some unity.
Plants are also not in rows but in drifts, and there might be three or four drifts of the same plant used in a long border. Often borders are created against a fence, wall or row of shrubbery and are quite deep, allowing for the use of tall plants without making them appear out of scale. Using a lot of tall plants in a narrow island bed would not appear in scale with the size of the border, but island beds are not commonly used in modern landscapes.
Using tall annuals in some of the drifts in a mixed border has several advantages. First, many annuals bloom until freeze-up while many perennials flag long before late fall. Therefore, including some annuals in a mixed border will ensure a continuity of bloom during the whole growing season. Clumps of annuals can provide vibrant colour among the often more subdued hues of perennials. Because tall annuals are quite large few plants are required, and if started from seed (many annuals are easy to grow from seed), the cost is minimal. Finally, some interesting combinations of plants can be achieved when using some tall annuals in a mixed border.
Here’s some examples:
Cosmos, particularly the tall variety “Sensation,” provide sturdy plants that produce white, pink and dark-maroon flowers that will bloom all summer. Deadheading will ensure that they keep on blooming. Cosmos like moist soil and full sun. They will not object to standing shoulder to shoulder with clumps of perennials. Their ferny foliage is an added benefit.
There are many varieties and they produce heavy plumes of bloom held above sturdy plants. Some varieties produce deep-wine plumes and others golden-orange plumes; both will look great in a mixed border where they will create interesting focal points. They like full sun. The variety “Love-Lies-Bleeding” has long ropes of bloom that cascade rather that standing erect like other varieties, which creates an interesting effect.
Both the white and the pink varieties produce blooms that have the sheen of satin. They are big plants and just a few will create a fair-size grouping in a mixed border. Deadheading will encourage new bloom. Lavatera likes a sunny exposure and moist, rich soil.
Commonly called spider flower because its blooms resemble huge spiders, cleome can provide clumps of pink and white colour in a mixed border. The plants bloom all summer and are over a metre tall. Cleome likes sun and heat but requires consistent moisture.
The attractive spikes of bloom can reach a height of 50 cm and come in a range of colours from white through pink and red to dark purple. Larkspur likes sun but will tolerate some shade and the lovely double flowers on the spikes resemble delphinium.
The highly scented nicotiana sylvestris produces pendant clusters of white blooms. This variety is grown for its perfume and for its pure-white blooms. It is taller than other nicotiana varieties, reaching a height of over a metre and a half.
There are several other annuals well suited to use in mixed borders, and using tall ones provides a whole new dimension. Give this technique a try.