Fertilising guide
How to fertilise Rosemary (Rosmarinus officinalis)— schedule & NPK
Also called Rosemary, Common Rosemary.
More about rosemary
About Rosemary
Rosmarinus officinalis · also called Rosemary, Common Rosemary · herb
An iconic evergreen Mediterranean shrub with aromatic, needle-like leaves used widely in culinary and ornamental settings. Thrives in full sun and well-drained, lean soil; highly drought-tolerant once established. Hardy in USDA zones 8–11, with cold-hardy cultivars surviving in zone 6–7. Produces pale blue flowers in spring and sporadically through the year.
Growth habit: Upright, bushy, evergreen shrub with dense, woody stems and narrow, needle-like grey-green leaves with silvery undersides
What fertiliser rosemary actually wants — and why
Rosemary is a soft, fast leafy herb that you harvest hard — a modest balanced feed keeps tender growth coming without tipping it into bland or bolting.
A balanced general feed (even N-P-K) at modest strength — enough nitrogen to keep replacing the leaves you pick, but not so much that flavour thins or it bolts to seed.
For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for rosemary: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.
How often to feed rosemary, and which months
Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For rosemary:
Apply a light dressing of balanced granular fertiliser in spring only. Avoid feeding in late summer or autumn as this stimulates soft, frost-susceptible growth. Overly fertile soil reduces essential oil concentration and hardiness. In practice: a balanced liquid feed every few weeks through the main growing and harvesting season (spring through early autumn), more often the harder you are picking it.
The dormant-season rule matters more than the exact interval: skip feeding entirely when rosemary is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.
What strength to mix for rosemary
Half strength is a sensible default for rosemary — enough to fuel regrowth after cutting, gentle enough that the leaves stay aromatic rather than watery.
Feeding always goes onto already-damp soil, never dry roots — water rosemary first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the rosemary watering schedule.
Signs you are over-feeding rosemary
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for rosemary:
- Fast, soft, pale growth with diluted, less aromatic flavour.
- Early bolting (running to flower) and a bitter edge.
- Salt crust and scorched tips on container plants.
Signs you are under-feeding rosemary
- Pale, slow regrowth after cutting and small leaves.
- A tired, stalled plant that cannot keep up with harvesting.
- Yellowing older leaves in a long-spent pot.
If the symptoms point at watering, light or roots rather than nutrition, the full rosemary care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Pot-grown rosemary builds up feed salts quickly — water until it drains each time and flush the pot with plain water every few weeks, especially on a sunny windowsill.
Organic vs synthetic feeds for rosemary
Organic options
A diluted seaweed feed or worm-casting tea keeps soft growth coming without overdoing it. UK: dilute seaweed or Westland; US: Espoma Garden-tone or Neptune's Harvest. Gentle, hard to overdo, flavour-friendly.
Synthetic / liquid feeds
A balanced liquid feed at half strength through harvesting — UK: Phostrogen, Baby Bio or Westland; US: Miracle-Gro all-purpose at half strength. Fast regrowth; just do not overdo the nitrogen.
Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.
Fertilising rosemary — frequently asked questions
What fertiliser does rosemary need?
A balanced general feed (even N-P-K) at modest strength — enough nitrogen to keep replacing the leaves you pick, but not so much that flavour thins or it bolts to seed. Rosemary is a soft, fast leafy herb that you harvest hard — a modest balanced feed keeps tender growth coming without tipping it into bland or bolting.
How often should I feed rosemary?
Apply a light dressing of balanced granular fertiliser in spring only. Avoid feeding in late summer or autumn as this stimulates soft, frost-susceptible growth. Overly fertile soil reduces essential oil concentration and hardiness. Apply a light dressing of balanced granular fertiliser in spring only. Avoid feeding in late summer or autumn as this stimulates soft, frost-susceptible growth. Overly fertile soil reduces essential oil concentration and hardiness. In practice: a balanced liquid feed every few weeks through the main growing and harvesting season (spring through early autumn), more often the harder you are picking it.
What strength of feed for rosemary?
Half strength is a sensible default for rosemary — enough to fuel regrowth after cutting, gentle enough that the leaves stay aromatic rather than watery.
What does over-feeding rosemary look like?
Fast, soft, pale growth with diluted, less aromatic flavour. Early bolting (running to flower) and a bitter edge. Salt crust and scorched tips on container plants. Over-feeding rosemary with strong nitrogen is the usual mistake — it grows fast and lush but the leaves turn bland and it bolts to flower sooner, ending the useful harvest early.
Should I flush the soil of rosemary?
Pot-grown rosemary builds up feed salts quickly — water until it drains each time and flush the pot with plain water every few weeks, especially on a sunny windowsill.
Keep reading
- Rosemary care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water rosemary — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise boneset
- How to fertilise betony
- How to fertilise greek sage
- All 6887 fertilising guides in the Growli library