After a glorious blaze of flowers, hydrangeas add superb autumn colour to the garden.

I always associate them with coastal gardens, where the sea's intense light enhances the brilliance of their deep, blue flowers. These blooms are wonderfully large, comprising small fertile florets with larger, flat, sterile or ray florets shaped almost like mopheads.

Although there are many different hydrangeas, for most of us these mopheads instantly spring to mind. Blue is the default colour but blue turns pink in more alkaline or neutral soils. To stay blue, hydrangeas need to absorb aluminium, an element which dissolves more readily in acidic ground, making it readily available to the shrubs.

Coastal parts of Scotland - especially in the west - and many inland areas have acidic soil, so are ideal for hydrangeas. But if you have neutral soil, as I do, be sure to avoid the couthy old method of planting your hydrangea on a bed of rusty nails. It's safer to buy a product containing aluminium sulphate. Needless to say, hydrangeas can also intentionally have pink or white flowers.

Mopheads, hortensias, are one of two types of Hydrangea macrophylla. They've been grown in Japanese gardens for centuries and, despite being slightly poisonous, were used as herbs or in sweet herbal teas. Plant hunters first brought them to Europe in the 18th century and, like all plants, they've fallen in and out of fashion. Currently, hydrangeas are in vogue, featuring in a fair number of show gardens.

Every year sees new varieties of hortensia springing up. Mopheads are hardy and should grow well almost anywhere here. All Summer Beauty and Endless Summer produce superb snowball-like, deep blue flowers on new as well as old wood, so they cope in a frost pocket. The specially hardy Blue Bonnet, is as deeply blue as they come.

Lacecap hydrangeas are a little more subtle. The mass of large sterile florets on hortensias is replaced by lots of small fertile florets surrounded by fewer large ray ones. Veitchii is particularly striking and, like many hydrangeas, the flowers turn pink with age. It will cope with a little shade but needs a sheltered spot. Meanwhile, Teller comes in deep blue, white or pink.

The toughest of all, paniculatas, are a little taller than mopheads and lacecaps, but their flower heads are quite different. These hydrangeas produce superb conical panicles of creamy white fertile flowers with fairly large, pink-white rays. For me, nothing can beat Phantom's magnificent display.

Paniculatas were one of the 838 Japanese plant varieties in a Dutch catalogue of 1863. When working in Japan with the Dutch East India Company in the 1820s, a cataract specialist, PFB von Siebold, embarked on a lifelong love of Japanese plants.

In early 19th-century Japan, life was very difficult for Europeans. Travel within the country was restricted and, to become his wife, von Siebold's Japanese paramour first had to be declared a prostitute and freely available to every member of the Dutch community. Acquiring plants was equally difficult, as was transporting them to Europe. After being rescued from a sinking ship in Japan, many of them were trampled underfoot during a fierce battle that raged in von Siebold's Dutch garden in 1830. In a less dramatic visit to Japan in 1862, von Siebold added H paniculata to his catalogue.

A second hydrangea on von Siebold's list was petiolaris, the climbing hydrangea. This specimen readily carpets a wall or a tree, first with its glorious white blossom and then tranquil yellow leaves in autumn. Although slow to get started, petiolaris can reach an impressive 15 metres. The low light levels in Scotland make it better suited to an east-facing wall, rather than the north-facing one that's often recommended in catalogues.