Growing black walnut 'thomas' in a pot

Black Walnut 'Thomas' can be grown in a container while young, but it reaches about 22 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.

Black Walnut 'Thomas' needs sharp drainage, so this matters more in a pot than in the ground. Use a free-draining mix (add perlite, grit or bark to standard compost), always pick a container with drainage holes, and never let it stand in a saucer of water.

Containers dry far faster than open ground, so black walnut 'thomas' in a pot needs checking more often than the general guidance of "Deep watering every 10-14 days in dry spells; weekly for young trees" — especially in summer, wind, or a heated room. Check the top few centimetres with a finger rather than watering on a fixed day.