Growing clethra alnifolia 'ruby spice' in a pot

Clethra alnifolia 'Ruby Spice' can be grown in a container while young, but it reaches about 8 m, so a pot is a medium-term home rather than a permanent one. Start it in a 40-60 cm (16-24 in) across planter, expect to pot on as it grows, and accept that container life will keep it smaller than it would be in open ground — which is often exactly what people want.

Aim for a container 40-60 cm (16-24 in) across. Pot on when roots show through the drainage holes or growth slows noticeably — usually every 1-2 years for a plant this size. Move up one pot size only; jumping several sizes leaves wet compost the roots cannot reach, and that is what rots them.

Clethra alnifolia 'Ruby Spice' likes steady moisture but not waterlogging — a tricky balance in a pot. Use a good peat-free compost with some added perlite for air, make sure the container drains freely, and mulch the surface to slow evaporation.

Containers dry far faster than open ground, so clethra alnifolia 'ruby spice' in a pot needs checking more often than the general guidance of "Keep soil consistently moist; water deeply 1-2 times weekly in the first two seasons and during drought" — especially in summer, wind, or a heated room. Check the top few centimetres with a finger rather than watering on a fixed day.