How to Grow Costmary
Tanacetum balsamita
Costmary is a hardy, spreading perennial herb grown for its large, oval, balsamic-scented leaves. Plant in full sun in well-drained soil and give it space — it spreads via rhizomes and will slowly colonise surrounding ground. Once established it needs little care — just a spring tidy, occasional division, and regular leaf harvests. Yellow button flowers appear in late summer and are worth leaving for pollinators. Cut back hard in autumn as the plant dies back, and expect reliable re-emergence each spring.
Yearly Lifecycle
Care Essentials
Little feeding needed. A light top-dressing of compost in spring is sufficient. Avoid nitrogen-heavy feeds which promote lush but less fragrant foliage.
Watch For
- Aphids on new growth
- Powdery mildew in humid conditions
- Slugs on young shoots
Companions
Lavender, Sage, Lemon balm, Rosemary
Care Requirements
Light
Full sun preferred; tolerates light shade
Grows best in full sun, which intensifies the leaf fragrance. Tolerates partial shade but becomes more lax and less aromatic. Best sited against a south-facing wall or in an open, sunny border.
Watering
Low water needs once established
Drought-tolerant once established. Water during prolonged dry spells in the first season. Avoid waterlogged soil, which causes root rot. Good drainage is more important than irrigation.
Fertilizing
Minimal feeding; compost mulch in spring
Costmary thrives in average to poor soil. A light top-dressing of garden compost in spring is all that is needed. Avoid high-nitrogen feeds, which produce large but less fragrant leaves.
Pruning
Cut back in autumn; divide every 2–3 years
Remove spent flower stems after blooming. Cut the whole plant back hard in autumn as the foliage dies back. Divide spreading clumps every 2–3 years in spring to keep plants vigorous.
Spacing
60 cm apart; contain if space is limited
Plants spread steadily via rhizomes. Space at 60 cm to allow for spread. In small gardens, sink a physical root barrier to limit spread, or grow in a large container.
Spacing & Planting
| Plant spacing | 60 cm |
| Row spacing | 60 cm |
| Mature height | 80 cm |
| Mature spread | 60 cm |
Spreads via rhizomes and will colonise a wide area over time. Allow 60 cm between plants or contain with buried edging. Divide every 2–3 years to keep clumps vigorous.
