Clematis is the plant that confuses more gardeners than almost any other, and the confusion nearly always comes from the same source. Someone cuts back their clematis at the wrong time of year, loses a season of flowers as a result, and concludes either that they have done something wrong or that clematis is difficult. It is not difficult. It is specific. The single most important thing to understand about pruning clematis is that different types require completely different approaches, and applying the wrong approach, even a well-intentioned one, will cost you flowers. Before you pick up a pair of secateurs, you need to know which group your clematis belongs to. Everything else follows from that.

The horticultural world divides clematis into three pruning groups, and while the categories carry numbers rather than names, the logic behind them is straightforward. Group 1 clematis flower on the previous year's wood and need little or no pruning. Group 2 clematis flower on both old and new wood and need a light tidy in late winter. Group 3 clematis flower entirely on the current season's new growth and are cut back hard in early spring. Getting these three groups clear in your mind is the foundation for everything that follows. If you do not know which group your clematis belongs to and have lost the label, the simplest approach is to watch when it flowers and what the flowers look like. Flowering time and flower size together will tell you what you need to know.

Group 1: Montana, alpina, armandii, cirrhosa and Avalanche

Group 1 contains most of the clematis that cause the most damage when people prune them at the wrong time. These are the spring-flowering species that produce their flowers on growth made the previous year. Cut them in late winter or early spring and you are removing the flowering wood before it has had the chance to do what it was going to do. The result is a green plant with no flowers, and that is a frustrating outcome from what felt like a perfectly reasonable tidy-up.

Clematis montana is the most widely grown member of this group in Irish gardens. It is vigorous to the point of being rampant in the right conditions, covering large areas of wall, fence or tree with a mass of small flowers in April and May. The colour of those flowers depends on the variety, ranging from white in the species form through to the deep pink of varieties like Rubens and Tetrarose, but the timing is consistent across all of them. The rule with montana is to prune immediately after flowering, which in Irish conditions typically means May into early June. At that point you can cut back whatever has grown beyond where you want it, shortening stems to a healthy bud and removing anything that has become tangled or dead. What you are not doing is cutting into the main framework unless the plant has genuinely grown too large for its position. If it has, phase the reduction back over two or three seasons rather than attempting everything at once. A montana that is hacked back hard in one go can take two or more years to recover its flowering. In a sheltered Irish garden with a warm wall behind it, a montana will grow with extraordinary vigour, so keeping on top of it annually after flowering is considerably easier than trying to recover it after several years of neglect.

Clematis alpina and macropetala both sit in Group 1. They are smaller, more delicate plants than montana, producing nodding bell-shaped flowers in April and May, and they need the same light post-flowering tidy rather than any hard pruning. They are excellent choices for a north or east-facing wall in an Irish garden, tolerating less sun than most clematis and often performing better in the shadier positions where other climbers struggle. Prune them immediately after flowering, remove any dead or crossing stems, and leave the framework alone.

Clematis armandii is the evergreen clematis most commonly grown in Irish gardens. It produces clusters of small white or pale pink flowers with a pronounced vanilla fragrance in March and April, and it holds its long, glossy dark leaves year round. The pruning approach is the same as for the other Group 1 clematis: prune lightly immediately after flowering, which for armandii means April. The important caveat with armandii is that it does not respond well to hard renovation pruning. An established armandii that has been cut back severely is unlikely to regenerate freely and can take years to recover anything like its former state. Keep on top of it annually with a light trim after flowering and you will never need to do anything dramatic. The other significant consideration with armandii in Irish conditions is shelter. It is less hardy than montana and the long leaves are susceptible to wind scorch. A sheltered south or west-facing wall suits it considerably better than an exposed position.

Clematis cirrhosa, including the popular varieties Freckles and Wisley Cream, is the winter-flowering evergreen clematis. It produces small, nodding, often speckled flowers from November through to February, making it one of the most useful climbers in an Irish garden through the darkest months. As a Group 1 clematis it should be pruned immediately after flowering, which for cirrhosa means late February or early March as the last flowers finish. Beyond a light tidy to remove spent flowers and any damaged growth, very little intervention is needed. One note on cirrhosa that surprises people: it can look remarkably tired and brownish through the summer months, which is simply its natural semi-dormant period. It should not be cut back at this point. As temperatures drop in autumn it will come back into growth and be in full evergreen condition for its winter flowering season. Clematis Avalanche, which is a hybrid between two New Zealand species, also sits in Group 1 and follows the same pruning approach, flowering in spring on the previous year's wood.

Group 2: Large-flowered hybrids and Florida types

Group 2 clematis produce their flowers on both old and new wood, which gives them two flowering periods in a season. The main flush comes in May and June on stems produced the previous year, and a second, often lighter flush follows later in summer on the new growth produced after the first flowering. Varieties in this group include the classic large-flowered hybrids such as Nelly Moser and Niobe, as well as the more intricate Florida types including Sieboldii, which produces its distinctive purple-centred white flowers on new growth through summer and autumn.

The pruning for Group 2 in late February is gentle rather than dramatic. Work your way down each stem from the top until you reach a healthy pair of buds, and cut just above them. Remove any dead or damaged stems entirely. The goal is to tidy the plant and encourage strong new growth without removing the old wood that carries the early flowers. After the main June flush has finished, deadheading back to a bud below the spent flower can encourage the second flush. Group 2 clematis are the most forgiving of the three groups in terms of pruning because even a harder-than-intended cut in late February will not kill the plant, though it may reduce the early flower display for that season.

Group 3: Viticella, tangutica, texensis and herbaceous types

Group 3 clematis flower entirely on new growth produced in the current season. This means that everything produced the previous year is spent wood carrying no flowering potential, and cutting it back hard each February gives the plant a clean start and produces a better display than leaving it unpruned. Viticella varieties are the best known and most widely grown Group 3 clematis in Ireland, producing a mass of small flowers in purple, red, pink and white from June through to September. They are among the easiest and most rewarding clematis to grow in Irish conditions, tolerant of a range of soils and aspects and remarkably free-flowering once established.

For Group 3, prune in late February to a pair of strong, healthy buds around 30 to 45cm above ground level. It feels drastic if you have not done it before. The plant that was covering its support the previous summer is cut back to a short framework of stems close to the ground. By late May the new growth will be well underway, and by July the plant will have returned to full flowering height. Do not be tempted to leave some of the old growth unpruned thinking it will give you an earlier display. It will not, and the result is an increasingly tangled plant that flowers progressively higher and is harder to manage each year.

Clematis tangutica belongs in Group 3 and follows the same hard February prune. It is a species clematis rather than a hybrid, producing small golden-yellow lantern flowers from July through to September, followed by exceptionally decorative silky seedheads that persist well into winter. Bill MacKenzie is the most commonly grown form and is an excellent plant for an Irish garden, tolerating some exposure and performing well in a range of conditions. Clematis texensis, the scarlet clematis, is also Group 3, producing its tulip-shaped flowers in red and pink shades later in summer. Both benefit from the same hard cut each February.

Herbaceous clematis are perhaps the least understood category of the genus. These are clematis that do not climb but grow as freestanding or sprawling herbaceous perennials, dying back to the ground each winter and regenerating from the base each spring. Clematis integrifolia and its hybrids are the most commonly encountered, producing nodding blue or violet flowers through summer on stems that reach around a metre in height before flopping outward unless given some support. They sit in Group 3 and are simply cut back to the ground in late winter, typically February, as you would any other herbaceous perennial. They are reliable, long-lived plants that thrive in Irish conditions and are considerably more useful in a mixed border than most people realise.

One Irish-specific consideration worth mentioning for any clematis being grown through a hedge or into a tree: the Wildlife Acts restrict cutting vegetation between March and August where birds may be nesting. A vigorous montana or viticella grown through a hawthorn or holly hedge may be impossible to prune without disturbing nesting habitat during the nesting season. Check the plant and its host carefully before any pruning, and if there are active nests present, wait. The same Wildlife Act principle applies to all cutting and pruning in Irish gardens through the growing season, and clematis is no exception. The soil around clematis is also worth attending to. These are deep-rooting, hungry plants that respond well to a rich growing medium. Working a biochar-enriched compost into the root zone at planting time and as a top dressing each spring gives the plant the structure and biological activity it needs to produce strong new growth after pruning, particularly in the heavier Irish soils where drainage can be an issue. If you are not sure which group your clematis belongs to, or if something about your plant is not matching the descriptions above, tell me about your garden and I can advise on the right approach for what you have.