Spirea

Light and exposure

Spirea grows equally well in full sun or partial shade, which makes it one of the easiest shrubs to place anywhere in the garden. It flowers most generously in full sun, especially the summer varieties such as Japanese spirea, whose pink flower heads look a little duller in shade. Spring-flowering spireas are more forgiving and still put on a fine show even against a north-facing wall.

In gardens around Herve you see it everywhere: as an informal low hedge, in a mixed shrub border, or as a stand-alone specimen near a terrace. It asks for no special siting or wind shelter, and copes perfectly well planted alongside other shrubs in a mixed hedge.

Watering

A well-established spirea needs almost no watering at all. During its first year after planting, water it once or twice a week in dry spells to help the roots settle in, especially if you planted in spring rather than autumn. After that, it manages perfectly well on Belgian rainfall alone, even through the drier summers we have been getting more often.

A generous watering during flowering, if a dry spell hits in May or July depending on the type, keeps the blooms going longer and stops them from scorching too quickly. Grown in a pot, which is unusual for this shrub outside of nurseries, keep an eye on the compost, since it dries out faster than open ground.

Soil and repotting

Spirea is not fussy about soil at all. Ordinary garden soil, even on the poor or slightly chalky side, suits it without any special preparation. This is one of its real strengths in the sometimes heavy clay we have around Herve: it shrugs off conditions that would sulk other shrubs.

It does prefer soil that is not permanently waterlogged, though. On very heavy, compacted clay, loosen the planting hole well and work in some compost or coarse sand to help drainage. Once settled in, spirea tolerates dry, poor ground just as readily as the richer soil found elsewhere in the garden.

Temperature and humidity

This is a genuinely hardy shrub in our climate. Most garden spireas shrug off frosts of minus twenty degrees or more, which puts them entirely out of danger from anything winter in the Herve region can throw at them, even the harshest winters of recent decades. No winter protection is needed, not even for a shrub planted that same autumn.

In summer it copes just as well with heat and dry spells without visible suffering, apart from a slightly shortened flowering period during a prolonged heatwave. You will never need to mulch or fleece a spirea against frost, nor worry about it during a summer hot spell.

Pruning and upkeep

Pruning is the one technical point that needs some thought with spireas, and it is where most gardeners get it wrong. Everything depends on which type you have. Spring-flowering spireas, such as bridal wreath spirea with its white April cascades, or Vanhoutte spirea, flower on wood formed the previous year. Prune these right after flowering, never in winter: shorten the branches that have just flowered and, every two or three years, remove a few of the oldest stems at the base to open up the shrub. Prune these spireas in late winter and you cut off almost all of next year’s flowers, the classic mistake.

Summer-flowering spireas, such as Japanese spirea or its golden-leaved varieties, flower instead on the current year’s growth. Cut these back hard in late winter, before the buds break, leaving only twenty to thirty centimetres of old wood above ground. This hard pruning does not weaken the plant, it actually spurs the vigorous new growth that will carry the summer flowers. A summer spirea that never gets this treatment gradually loses vigour, flowers less each year, and ends up bare at the base.

Pests and diseases

Spirea is one of the healthiest shrubs you can plant, sailing through the seasons without any treatment in the vast majority of gardens. The one recurring nuisance is aphids, which sometimes colonise the tender new shoots of summer spireas just after the hard late-winter prune. A firm jet of water or a spray of soft soap is usually enough to see them off without reaching for an insecticide.

Powdery mildew can occasionally leave a white felting on the foliage in hot, humid weather, mostly on plants that are too crowded or poorly ventilated at the centre. Under Belgian conditions this stays a minor issue and rarely calls for treatment: an annual prune that opens up the centre of the shrub is usually enough to keep the risk down.

Propagation

Taking cuttings is by far the easiest way to multiply a spirea, and it works almost every time. In June or July, take softwood cuttings ten to fifteen centimetres long from the current year’s still-flexible growth, strip the lower leaves and plant them in a light mix of compost and sand, in partial shade. Rooting usually takes three to six weeks, and the young plants can go into the ground the following autumn or spring.

A slower but equally reliable option is to take hardwood cuttings in autumn or winter, fifteen to twenty centimetres of firmer wood, and plant them straight into open ground in a sheltered corner. Some spireas also send up suckers from the base that you can simply sever with some roots attached to start a new plant.

Month-by-month care calendar

Green Hub tips

• Before you reach for the secateurs, always identify your spirea’s type: white spring flowers mean pruning right after flowering, pink summer flowers mean a hard cut back in late winter.
• Never prune a spring spirea in winter or late winter, you would be cutting off almost all of next year’s flowers.
• To multiply a fine plant for free, take a soft shoot in June or July and root it in a light mix in partial shade, it almost always takes.
• Do not hold back on cutting summer spireas hard every year in late winter: the harder the prune, the more generous the summer flowering.