Fertilising guide
How to fertilise Rosemary (Salvia rosmarinus)— schedule & NPK
Also called common rosemary, garden rosemary.
About Rosemary
Salvia rosmarinus · also called common rosemary, garden rosemary · herb
Rosemary is a Mediterranean evergreen shrub with needle-like aromatic leaves used widely in cooking. It loves sun and free-draining soil and dislikes wet feet, especially in winter. Hardy in mild climates; container-grown elsewhere. Pet-safe by ASPCA standards.
Rosemary, Salvia rosmarinus (formerly Rosmarinus officinalis, family Lamiaceae), is native to the Mediterranean basin and adjacent dry parts of southern Europe, North Africa and western Asia, growing wild in hot, dry, rocky scrubland.
A low-nutrient Mediterranean subshrub that needs minimal feeding; rich soil or heavy fertiliser produces soft, floppy, less aromatic growth rather than a stronger plant.
Growth habit: Woody evergreen subshrub
Sources: plants.ces.ncsu.edu, missouribotanicalgarden.org, kew.org
What fertiliser rosemary actually wants — and why
Rosemary is a lean, aromatic herb — the essential-oil flavour you grow it for is strongest in poor soil, so feeding it actively makes it worse.
Little or nothing. If anything, a very weak balanced feed or a thin compost top-dress — never a rich nitrogen feed, which dilutes the aromatic oils and produces soft, bland, floppy growth.
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:
Very light feeder — a quarter-strength balanced feed once or twice a season is plenty. In practice: a spring compost top-dress at most, and otherwise leave rosemary unfed — lean, sharp-draining soil is exactly what concentrates its flavour.
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
As weak as it gets for rosemary, or none at all. The flavour-versus-growth trade-off runs the opposite way to leafy crops: restraint is the technique.
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:
- Lush, soft, fast growth with noticeably weaker scent and flavour.
- Floppy stems, sparse essential oils, and poor cold/wet hardiness.
- Salt crust in containers and scorched leaf tips from over-feeding.
Signs you are under-feeding rosemary
- Rare — these herbs thrive on lean soil.
- Only on truly exhausted soil: pale, thin, very slow growth.
- A short-lived, weak plant in a long-spent container.
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
Over-feeding is so unlikely with rosemary that flushing is rarely needed; if a container has had feed, a single plain-water flush and a switch to a leaner, grittier mix resets it.
Organic vs synthetic feeds for rosemary
Organic options
A thin spring mulch of garden compost or leaf-mould is the most these want. UK: a little garden compost; US: a light Espoma Garden-tone top-dress at most. Lean and gritty beats fed and rich every time.
Synthetic / liquid feeds
Generally none for rosemary. At absolute most, a very dilute balanced feed once or twice in a container; in the ground, nothing — synthetic feeds work directly against the flavour.
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?
Little or nothing. If anything, a very weak balanced feed or a thin compost top-dress — never a rich nitrogen feed, which dilutes the aromatic oils and produces soft, bland, floppy growth. Rosemary is a lean, aromatic herb — the essential-oil flavour you grow it for is strongest in poor soil, so feeding it actively makes it worse.
How often should I feed rosemary?
Very light feeder — a quarter-strength balanced feed once or twice a season is plenty. Very light feeder — a quarter-strength balanced feed once or twice a season is plenty. In practice: a spring compost top-dress at most, and otherwise leave rosemary unfed — lean, sharp-draining soil is exactly what concentrates its flavour.
What strength of feed for rosemary?
As weak as it gets for rosemary, or none at all. The flavour-versus-growth trade-off runs the opposite way to leafy crops: restraint is the technique.
What does over-feeding rosemary look like?
Lush, soft, fast growth with noticeably weaker scent and flavour. Floppy stems, sparse essential oils, and poor cold/wet hardiness. Salt crust in containers and scorched leaf tips from over-feeding. Feeding rosemary like a leafy vegetable is the defining mistake — rich nitrogen gives you a big, soft, fast plant whose leaves are watery and bland, with weak winter-rot resistance.
Should I flush the soil of rosemary?
Over-feeding is so unlikely with rosemary that flushing is rarely needed; if a container has had feed, a single plain-water flush and a switch to a leaner, grittier mix resets it.
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 basil
- How to fertilise herb garden
- How to fertilise mint
- All 200 fertilising guides in the Growli library