Choosing a hydrangea by flower colour alone is an easy way to end up with the wrong plant for the position. The main garden types differ in more consequential ways: flower shape, mature habit, tolerance of sun or shade, the wood on which they flower and the amount of space they eventually occupy. These differences affect not only how the plant looks, but where it will grow well and how it should be managed.

This guide concentrates on the six groups most useful when making that choice: mophead, lacecap, panicle, smooth, oakleaf and climbing hydrangeas. There are other species, including Hydrangea serrata and H. aspera, but the six groups below account for the principal distinctions a gardener is likely to encounter. For planting and general care rather than selection, the broader guide to growing hydrangeas in Ireland covers the subject in more detail.

The main types of hydrangeas at a glance

• Mophead hydrangeas: broad, rounded flower heads, most commonly associated with Hydrangea macrophylla; usually happiest where moisture is dependable and the hottest sun is avoided.
• Lacecap hydrangeas: flatter flower heads with small fertile flowers in the centre surrounded by larger showy florets; visually lighter and more informal than mopheads.
• Panicle hydrangeas: upright shrubs with conical flower heads, usually opening white or cream and often developing pink tones as they age; they flower on new growth and tolerate more sun.
• Smooth hydrangeas: Hydrangea arborescens, including ‘Annabelle’, with rounded white or greenish-white heads and flowers produced on the current season's stems.
• Oakleaf hydrangeas: Hydrangea quercifolia, grown as much for its deeply lobed foliage, autumn colour and ageing bark as for its conical flowers.
• Climbing hydrangeas: self-clinging woody climbers with broad, lacecap-like white flowers, particularly useful on shaded walls and mature trees.

Once the broad group is clear, cultivar choice becomes much easier. Laurel's Hydrangea collection brings the groups together, while the more specific collections below are useful when a particular flower form or growth habit is already decided.

Mophead hydrangeas: the classic rounded flower heads

Mophead is a description of flower form rather than a botanical species, although in gardens it is most closely associated with Hydrangea macrophylla. The showy sepals dominate the flower head and create the familiar dome or globe, usually in shades of blue, purple, pink, red or white. A mature H. macrophylla commonly forms a substantial rounded shrub, often around 1 to 2 metres in both directions, although cultivar differences are considerable.

These are particularly well suited to fertile soil that remains consistently moist without becoming waterlogged. Partial shade is useful, especially where afternoon sun would otherwise dry the soil or scorch the flowers, although the cool, moist character of many Irish gardens allows them to tolerate more light than they would in a hot, dry climate. Exposure matters. Even a plant with sufficient rainfall can suffer where persistent wind continually removes moisture from the large leaves.

Most traditional mopheads form their main flower buds on stems made during the previous season, so severe pruning at the wrong time can remove the following year's display. Some newer remontant cultivars can also flower on new growth, but that is a cultivar characteristic rather than something to assume of every mophead.

Hydrangea macrophylla ‘Ayesha’ shows how much variation exists within the group. Its rounded heads are unmistakably mophead in form, but the individual sepals are distinctly cupped rather than flat. For the broad, rounded effect characteristic of this group, the mophead hydrangeas collection is the most useful place to compare cultivars.

Lacecap hydrangeas: a lighter, more natural flower form

A lacecap flower is arranged quite differently. Small fertile flowers occupy the centre of a flatter inflorescence, with larger showy sepals forming a loose outer ring. The effect is more delicate than a mophead, and it combines particularly well with ferns, woodland planting and other foliage where an enormous rounded flower might feel too dominant.

Many familiar lacecaps are forms of Hydrangea macrophylla, so their cultural needs are broadly similar to mopheads: moisture-retentive but well-drained soil, shelter from drying winds and some protection from intense sun. Their pruning also requires the same caution because traditional forms generally depend on old wood for flowering. Lacecaps often have a shorter period of maximum floral display than mopheads, but their combination of fertile and sterile flowers gives them a more intricate character at close range.

Hydrangea macrophylla ‘Lanarth White’ is a strong example, with conspicuous white outer florets surrounding the flatter central portion of the flower. It is particularly effective where a white-flowered shrub is wanted without the visual weight of a solid mophead. Other cultivars can be compared in the lacecap hydrangeas collection.

Panicle hydrangeas: larger shrubs for more sun

Hydrangea paniculata is a very different plant. Rather than rounded or flat heads, it carries flowers in upright or spreading cones, with the showy sepals generally beginning white, cream or greenish-white and often developing pink or purplish tones as they mature. The species naturally makes a large shrub and can reach small-tree proportions, although modern cultivars range from compact plants to substantial specimens.

The most useful practical difference is that panicle hydrangeas flower on growth made in the current season. Winter damage to last year's flowering stems is therefore much less important than it is with a traditional mophead. They also perform better in stronger light, and flowering is usually most generous in sun, provided the soil does not become seriously dry. This makes them particularly useful where a H. macrophylla would be too dependent on shade or shelter.

Panicle hydrangeas also tend to extend the hydrangea season later into summer, and cooler conditions can prolong the attractive ageing colours of the sepals. Their scale suits mixed shrub borders, informal hedges and specimen planting particularly well. Hydrangea paniculata ‘Limelight’, which develops large lime-green flower heads that mature through the season, is a good illustration of the group's strong architectural flower form. The wider range sits within the panicle hydrangeas collection.

Smooth hydrangeas: reliable flowering from new growth

Smooth hydrangeas are forms of Hydrangea arborescens, a North American woodland species whose garden cultivars include some exceptionally large rounded flower heads. Like panicle hydrangeas, they flower on the current season's growth. They can therefore be pruned much harder without sacrificing the summer display, which is a useful distinction in gardens where old stems are regularly damaged or where a simple winter pruning routine is preferred.

They generally appreciate consistent moisture and light shade, although the amount of sun they tolerate increases where summers are cool and the soil remains moist. The famous weakness of some large-flowered forms is structural rather than climatic: when enormous flower heads become saturated after heavy rain, the stems may arch or fall outward. In an Irish garden this is worth considering before putting one in a position where a perfectly upright outline is essential.

Hydrangea arborescens ‘Annabelle’ is the classic example. Its very large rounded flower heads begin greenish, become creamy white and age towards green again, creating a much bolder effect than the species. It works particularly well where there is room for a loose, generous shrub rather than a rigid formal outline. The smooth hydrangeas collection contains this group.

Oakleaf hydrangeas: flowers, foliage and autumn colour

Hydrangea quercifolia earns its place for more than flowers. The leaves are deeply lobed in a form reminiscent of an oak, and they can colour richly through burgundy, red and purple in autumn. Older stems also develop peeling, cinnamon-brown bark, giving a mature plant a degree of winter character that most hydrangeas lack.

The flowers are conical, usually white or cream when fresh, with many cultivars ageing through pink and deeper reddish tones. Unlike panicle and smooth hydrangeas, oakleaf hydrangeas form their flower buds on old wood, so pruning should be conservative and carried out with future flowering in mind. They can grow in sun or considerable shade if moisture is adequate, but flowering tends to be stronger where the plant receives enough warmth and light.

That last point matters in Ireland. The foliage alone can justify the plant, but a cool, heavily shaded garden is not the position in which to expect its fullest floral performance. A brighter, sheltered site with good moisture gives it a better balance. Hydrangea quercifolia ‘Alice’ is a substantial cultivar and needs to be allowed real space as it matures; it is better treated as an important shrub in the composition than squeezed into a small gap. Other forms are grouped under oakleaf hydrangeas.

Climbing hydrangeas: for walls, trees and vertical space

The climbing hydrangea is not a shrub in the usual sense. Hydrangea anomala subsp. petiolaris, commonly sold as Hydrangea petiolaris, attaches itself to rough surfaces with aerial root-like holdfasts and can eventually cover a large wall or climb high into a mature tree. Young plants are characteristically slow to establish, but growth can accelerate markedly once a strong root system has developed.

Its broad white flower heads resemble loose lacecaps and are carried on established older growth. Partial shade suits it particularly well, making this one of the most useful flowering climbers for north-facing and east-facing walls. It can also grow in sun where soil moisture is sufficient, but its great advantage is its willingness to perform where many flowering climbers become sparse.

Mature plants become heavy, so the surface or structure needs to be capable of carrying them. The clinging roots can also leave marks if old stems are removed from masonry, which makes it better suited to permanent planting than to a wall where the climber may need to be taken down later. Hydrangea petiolaris is the straightforward species choice, while other forms can be found among the climbing hydrangeas. The separate guide to growing climbing hydrangeas deals with establishment, supports and long-term management in greater detail.

Which hydrangea type is best for your garden?

For the traditional rounded blue or pink hydrangea, a mophead remains the obvious choice, while a lacecap gives much of the same colour range and cultural behaviour with a lighter flower form. Where the position is sunnier, or reliable flowering after winter damage is important, a panicle hydrangea is usually the stronger choice. Smooth hydrangeas offer the same new-wood reliability with a softer woodland character and, in cultivars such as ‘Annabelle’, enormous rounded white flowers.

Oakleaf hydrangeas are better chosen where foliage, autumn colour and structure matter as much as summer flower, and they deserve a warm, reasonably sheltered position if flowering is a priority. A climbing hydrangea solves an entirely different problem by taking the genus upwards onto a shaded wall, substantial fence or mature tree.

Position and mature size should decide the group before flower colour decides the cultivar. Where light is the main limitation, the guide to hydrangeas in shade compares the types more closely. For confined spaces, growing hydrangeas in pots covers container-specific selection and care. Once the plant is chosen, it is also worth checking how to prune each hydrangea type, because the distinction between old wood and new growth is one of the most important differences between these otherwise closely related plants.