Fertilising guide
How to fertilise Purple Jerusalem Sage (Phlomis purpurea)— schedule & NPK
Also called Purple Jerusalem sage, Purple phlomis.
More about purple jerusalem sage
About Purple Jerusalem Sage
Phlomis purpurea · also called Purple Jerusalem sage, Purple phlomis · flowering
Phlomis purpurea is a handsome, upright evergreen shrub native to the dry hillsides and scrubland of southern Spain and Portugal, where it is one of the most widespread phlomis species in western Iberia. Its grey-white woolly leaves contrast beautifully with whorls of rosy-purple to lilac-pink flowers produced from late spring to early summer. Once established it is remarkably drought-tolerant, but adequate sun and free drainage are essential for long-term health. It is not listed on the ASPCA database and is classified as mildly-toxic due to insufficient confirmed pet-safety data.
Growth habit: Upright, branching evergreen shrub with grey-felted stems and leaves.
What fertiliser purple jerusalem sage actually wants — and why
Purple Jerusalem Sage is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula.
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 purple jerusalem sage: 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 purple jerusalem sage, 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 purple jerusalem sage:
Apply a light dressing of balanced, low-nitrogen fertiliser in spring; avoid autumn feeding, which produces soft growth vulnerable to frost. Treat that as sparingly through the growing season between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
The dormant-season rule matters more than the exact interval: skip feeding entirely when purple jerusalem sage 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 purple jerusalem sage
Half strength is the safe default for purple jerusalem sage — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
Feeding always goes onto already-damp soil, never dry roots — water purple jerusalem sage first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the purple jerusalem sage watering schedule.
Signs you are over-feeding purple jerusalem sage
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for purple jerusalem sage:
- Brown, crispy leaf tips and edges with no sign of underwatering.
- A white, crusty salt deposit on the soil surface or pot rim.
- Weak, pale, stretched new growth that flops.
- Lower leaves yellow and drop while the soil is correctly watered.
Signs you are under-feeding purple jerusalem sage
- Uniformly pale or yellow-green leaves, oldest first.
- Noticeably small new leaves and stalled growth in good light and season.
- A generally tired, lacklustre look despite correct watering and light.
If the symptoms point at watering, light or roots rather than nutrition, the full purple jerusalem sage care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of purple jerusalem sage with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Organic vs synthetic feeds for purple jerusalem sage
Organic options
A diluted seaweed or worm-casting feed, or fish emulsion if you can tolerate the smell indoors. UK: Westland or Baby Bio Organic, dilute seaweed; US: Espoma Indoor! or Neptune's Harvest fish & seaweed. Slow, gentle and hard to overdo.
Synthetic / liquid feeds
A general-purpose houseplant liquid at half strength — UK: Baby Bio, Westland Houseplant Feed or Phostrogen; US: Miracle-Gro Indoor Plant Food or Schultz. Convenient and fast-acting; the only risk is overdoing it.
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 purple jerusalem sage — frequently asked questions
What fertiliser does purple jerusalem sage need?
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula. Purple Jerusalem Sage is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
How often should I feed purple jerusalem sage?
Apply a light dressing of balanced, low-nitrogen fertiliser in spring; avoid autumn feeding, which produces soft growth vulnerable to frost. Apply a light dressing of balanced, low-nitrogen fertiliser in spring; avoid autumn feeding, which produces soft growth vulnerable to frost. Treat that as sparingly through the growing season between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
What strength of feed for purple jerusalem sage?
Half strength is the safe default for purple jerusalem sage — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding purple jerusalem sage look like?
Brown, crispy leaf tips and edges with no sign of underwatering. A white, crusty salt deposit on the soil surface or pot rim. Weak, pale, stretched new growth that flops. Lower leaves yellow and drop while the soil is correctly watered. Feeding purple jerusalem sage year-round on a fixed schedule, including dark winter months, is the most common mistake — it cannot use the nutrients in low light and the surplus simply burns the roots and crusts the soil.
Should I flush the soil of purple jerusalem sage?
Flush the pot of purple jerusalem sage with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Keep reading
- Purple Jerusalem Sage care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water purple jerusalem sage — 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 parsons juniper
- How to fertilise gold coast juniper
- How to fertilise old gold juniper
- All 10153 fertilising guides in the Growli library