How to keep hydrangeas happy
Bright blue, pink or white, hydrangeas are heavenly, says Monty Don. Here, he tells you how to help make them thrive
FOR most of my life hydrangeas have not been fashionable. My grandfather – who always called them hortensias, one of their common names – had some with acid blue flowers growing outside his front door and I remember, when I got old enough to notice such things, being bewildered that where we lived, just 60km away, there were plenty of pink hydrangeas but none that were blue.
This was, as most gardeners will know, because Hydrangea macrophylla responds to acidic soil by producing blue flowers, whereas a chalky, alkaline soil will turn them bright pink and in a neutral soil of around pH7 they’ll become a pinky mauve.
However, I like hydrangeas, particularly the lacecap types, whose flowers have a floating, shimmering quality, and they are a very useful plant because they will happily grow in dappled shade as long as the soil is not too dry.
I started with the climbing H. anomala subsp. petiolaris, which I grew on a very dark north-facing wall where it flourished exuberantly after a slow start. It is one of the few selfclinging climbers that has aerial roots; these have suckers that fix themselves to a wall or the trunk of a tree.
Over the past few years I have planted the lacecap ‘Lanarth White’, which has flattened heads of pink or blue flowers surrounded by brilliant white florets; the more abundantly floriferous mophead ‘ Madame Emile Mouillère’, which is covered with a great mass of white flowers in June and July; and H. paniculata ‘Floribunda’, which produces its flowers on new wood. So does the H. arborescens subsp. discolor ‘Sterilis’ I have in my spring garden – this has delicate, pretty white flowers but is a tough plant and particularly droughttolerant for a hydrangea.
The essential difference between mopheads and lacecaps is the way their flower heads are formed. Mopheads, the group that the bulk of the old hortensias belongedg to,, have domed flower heads made up almost entirely of large sterile sepals. Lacecap flower heads are flatter and have a central section of tiny, fertile florets – composed of both male and female flowers – which is surrounded by infertile sepals. In ‘Lanarth White’, for example, it is the tiny florets that respond to the soil pH and take on a blue or pink tinge while the sepals stay uniformly white.
Hydrangeas do best in light or dappled shade and hate becoming too dry, so make sure there’s lots o of organic matter in the soil before planting and mulch each year with a generous layer of compost or leaf mould. This especially applies to hydrangeas in pots, which need a regular soak.
Hydrangeas need to be pruned only to control or train the size and shape of the plant. As with all pruning it’s important to understand the growth habit of the plant. H. macrophylla forms its flowers in spring from buds that formed the previous summer. This means that if you prune in autumn or early spring you’ll have few if any flowers that year. Wait until you see new growth on the tips of the shoots (usually in April), and when you do prune, cut back the old flower heads to the first pair of healthy buds below them. Remove any very old, crossing or dead wood at this stage, cutting it right back to the base of the shrub. The regrowth will not bear any flowers until the next year.
H. paniculata produces its flowers on the current season’s wood so can be pruned back hard in spring – retain just a framework to carry the season’s flowering growth. If you’re uncertain what kind of hydrangea you have, simply observe whether the flowers form on new shoots or old and then prune accordingly the following year.
The spent flowers form an important protective layer for the emerging buds so should not be removed until after the last frosts as a hard frost in May can wipe out a year’s display of flowers.
If your hydrangeas are in pots it’s a good idea to cover them with horticultural fleece if a late frost is forecast. This will be enough to protect them from the effects of the frost and the even more damaging early morning sunshine that usually follows a cold May night.