Spirea in April: monthly care

Spiraea japonica thrives in full sun or partial shade, though flowering is most abundant in a sunny position. It tolerates a wide range of soils—loam, clay, or sandy—provided drainage is reasonable. Before planting, dig over the soil to a spade's depth and work in a bucketful of well-rotted compost or manure to improve structure and moisture retention, especially on light sandy ground. Plant container-grown spirea in March, April, May, September, or October. Avoid frosty or waterlogged conditions. Dig a hole roughly twice the width of the root ball and the same depth, so the top of the root ball sits level with the surrounding soil. Backfill with the excavated soil, firming gently with your heel as you go to eliminate air pockets. Space plants 96 cm apart if you're creating a low hedge or informal border; for a single specimen, allow at least 1 metre all round to accommodate the mature spread of 60–120 cm. Water thoroughly after planting—give each shrub a full watering can—to settle the roots. Apply a 5–7 cm layer of garden compost, bark chips, or leaf mould around the base, keeping the mulch a few centimetres clear of the stems to prevent rot. This mulch conserves moisture and suppresses weeds while the plant establishes. Newly planted spirea will need regular watering through the first growing season, especially during dry spells in late spring and summer, until the root system has spread into the surrounding soil.

Spiraea japonica flowers on the current season's growth, so prune in March or April before the new shoots emerge. This timing encourages a flush of vigorous stems that will carry flowers from early summer onwards. Use clean, sharp secateurs or loppers for thicker stems. Cut back all the previous year's growth hard—down to within 10–15 cm of the woody framework or to a pair of healthy buds low on each stem. Don't be timid: hard pruning rejuvenates the plant, promotes bushy growth, and maximises flowering. If your spirea has become congested or overgrown, remove one or two of the oldest, thickest stems entirely at ground level to open up the centre and stimulate fresh basal shoots. Deadheading spent flower clusters in late summer isn't essential but does tidy the plant and may encourage a modest second flush of bloom. Simply snip off the faded heads just above a leaf joint. If you prefer the russet seedheads for winter interest, leave them in place and tidy up during the main prune in spring. Mature spirea that have been neglected can be renovated by cutting the entire shrub down to 15–20 cm above ground level in March. Recovery is usually vigorous, though you will sacrifice flowers that year. Feed well after hard renovation and mulch to support regrowth.

Spiraea japonica has moderate water needs. Once established, it tolerates short dry spells but performs best with consistent moisture during spring and summer, especially in sandy soils. Water deeply every week to ten days in prolonged dry weather; reduce frequency in autumn and winter when rainfall is usually adequate. Avoid waterlogging, which can lead to root problems on heavy clay. Feed in March or April as growth resumes. Scatter a general-purpose granular fertiliser such as Growmore or blood, fish, and bone around the base at roughly 70 g per square metre, then water in or lightly fork into the soil surface. A second, lighter feed in late April can be beneficial on poor soils but isn't necessary on fertile ground. Over-feeding encourages soft, leafy growth at the expense of flowers. Mulch annually in spring with a 5 cm layer of garden compost, well-rotted manure, or bark to suppress weeds, retain moisture, and gradually improve soil structure. Keep mulch clear of the stems. Spiraea japonica is generally trouble-free. Aphids occasionally cluster on soft new growth in late spring; a strong jet of water or an insecticidal soap usually resolves the problem. Powdery mildew can appear as a white coating on leaves in dry summers, particularly in sheltered spots with poor air circulation; improve spacing and water at the base rather than overhead. This shrub is fully hardy across temperate Europe and requires no winter protection.