At a glance
The convolvulus family presents one of gardening’s more interesting contradictions. On one hand it contains some of the most beautiful annual climbers available – the vivid azure trumpets of Convolvulus tricolor and the vigorous flowering vines of the ornamental morning glories produce summer colour that few plants can match for sheer intensity. The deep blue of Royal Ensign, one of the most widely grown varieties, is as close to a true gentian blue as any summer annual achieves, and it earns its place in any sunny border on that quality alone. On the other hand, Convolvulus arvensis – field bindweed – is one of the most tenacious and difficult weeds in British gardens, capable of regenerating from the smallest root fragment and strangling other plants with remarkable efficiency.
Understanding which convolvulus to grow and which to eradicate is the starting point for any UK gardener. The ornamental species are well worth growing and easy to manage. The weedy species require a different approach entirely – one focused on persistent removal rather than cultivation. This guide covers both, with a particular focus on getting the best from the decorative annual and perennial types that bring real value to UK borders, containers and climbing structures through summer.
Types of convolvulus for UK gardens
The Convolvulaceae family is large and diverse, but for UK gardeners the relevant species fall into three clear groups: ornamental annuals grown for their flowers, ornamental perennials for permanent planting, and weedy species that should be treated as pests rather than plants. Getting clear on which is which before buying or sowing saves considerable frustration.
Sowing and growing
Convolvulus tricolor is the most widely grown ornamental species and one of the simplest to raise from seed in the UK. It is direct-sown into its final position from April onwards once the soil has warmed to at least 10 degrees Celsius. The seeds are large enough to handle easily and germinate reliably within 10-14 days in warm conditions. Sow two or three seeds together at 20-25cm spacings and thin to the strongest seedling once established. Starting indoors is possible but unnecessary and can cause root disturbance – direct sowing gives better results.
The tender perennial C. sabatius is grown from cuttings or bought as young plants in spring and planted out after the last frost – in most UK regions this means late May. It is well suited to hanging baskets and containers where its trailing habit can be displayed to best effect. Bring it under cover before the first frosts as it is not hardy enough to survive UK winters outdoors, though it will overwinter reliably on a bright windowsill or in a frost-free greenhouse.
Full sun is non-negotiable for convolvulus flowers. All ornamental convolvulus species open their flowers in response to direct sunlight and keep them tightly closed on overcast days. A position receiving fewer than 6 hours of direct sun per day will produce a disappointing display regardless of all other care. South or west-facing borders and containers are the correct locations.
Care and support
Convolvulus tricolor is a bushy rather than climbing plant despite being in a family of climbers. It does not twine or cling and needs no support structure – it grows into a compact mound of foliage topped with flowers. The trailing C. sabatius similarly needs no support and is better suited to hanging baskets and window boxes where it can cascade freely over the edge. The true climbing species in the family – the morning glories related to Ipomoea, which were historically grouped with Convolvulus – do need a support structure and are covered separately.
Feeding requirements are modest. Convolvulus tricolor performs best in moderately poor soil – rich soil pushes the plant into excessive leaf growth at the expense of flowers, mirroring the same principle that governs nasturtiums. Avoid adding fertiliser at planting time and do not feed during the growing season unless the plant shows signs of nutrient deficiency – pale, weak growth that is not attributable to overwatering. Container-grown C. sabatius benefits from a monthly balanced liquid feed from June to August as it cannot access soil nutrients in the same way.
Best varieties for UK gardens
Convolvulus tricolor offers a range of named varieties, all sharing the characteristic tricoloured trumpet flowers – typically with a white or yellow centre graduating to the main petal colour. The blue and purple forms are the most widely grown and produce the strongest colour impact, though the mixed varieties offer attractive variety in a single sowing. All varieties share the same habit – a compact, bushy mound 25-35cm tall – and the same sun-loving requirements. The flowers are individually short-lived, lasting only a day or two, but each plant produces buds continuously from June until the first frosts, giving a sustained display rather than a single flush. This makes convolvulus a reliable gap-filler in borders where later-summer colour is needed after spring bulbs and early perennials have finished.
Problems, pests and bindweed
Ornamental convolvulus species are largely trouble-free. The main threats are slug damage to seedlings in the weeks after germination – the large rounded leaves are attractive to slugs and in a wet spring some protection around young plants is worthwhile. Once established the plants grow vigorously and can tolerate moderate slug pressure. Aphids occasionally colonise soft new growth but rarely cause serious damage and natural predators typically bring populations under control without intervention. For any serious aphid infestation a targeted spray is an option but is rarely needed.
The larger challenge with the convolvulus family in UK gardens is field bindweed (C. arvensis). This native perennial weed is found in most UK garden soils, with a root system that extends to over 3 metres deep and regenerates readily from any fragment left in the ground. It twines around other plants, suppressing their growth, and the white or pale pink trumpet flowers – while individually pretty – indicate an established weed presence that will not disappear without sustained effort. Eradication requires persistent removal of all top growth throughout the growing season to starve the roots over time. Chemical control with systemic herbicides is effective but requires careful application to avoid contact with garden plants. For areas of bindweed removal, covering the ground with light-excluding membrane for a full growing season will weaken but rarely fully eradicate an established infestation.
Convolvulus tricolor is one of the most rewarding hardy annuals for sunny UK borders. The vivid blue flowers that appear through summer until the first frosts are attractive to butterflies and hoverflies, and the plant’s tolerance of poor dry conditions makes it useful in the same situations that suit other drought-tolerant annuals. Pair it with cosmos, marigolds or other sun-loving annuals for a long-season border that needs minimal attention once established.
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