Fertilising guide
How to fertilise Long-Leaved Phlomis (Phlomis longifolia)— schedule & NPK
Also called Long-leaved phlomis, Long-leaved Jerusalem sage.
More about long-leaved phlomis
About Long-Leaved Phlomis
Phlomis longifolia · also called Long-leaved phlomis, Long-leaved Jerusalem sage · flowering
Phlomis longifolia is an upright, grey-woolly shrub native to Turkey, Lebanon, and the eastern Mediterranean, recognisable by its unusually elongated, softly felted leaves and tall stems bearing whorls of bright yellow flowers in early summer. It is well suited to dry, sunny borders and gravel gardens where its bold, textural foliage provides year-round interest. Like all Mediterranean phlomis, it is intolerant of waterlogged soil and must have free drainage to thrive in wetter climates. Phlomis longifolia is not listed in the ASPCA database and is classified as mildly-toxic due to the absence of confirmed pet-safety information.
Growth habit: Upright, loosely branched evergreen shrub with notably long, strap-shaped, densely felted grey-green leaves.
What fertiliser long-leaved phlomis actually wants — and why
Long-Leaved Phlomis 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 long-leaved phlomis: 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 long-leaved phlomis, 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 long-leaved phlomis:
Apply a single low-nitrogen feed in spring; this species is adapted to infertile soils and over-feeding results in weak, floppy stems that are prone to wind and frost damage. 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 long-leaved phlomis 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 long-leaved phlomis
Half strength is the safe default for long-leaved phlomis — 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 long-leaved phlomis first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the long-leaved phlomis watering schedule.
Signs you are over-feeding long-leaved phlomis
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for long-leaved phlomis:
- 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 long-leaved phlomis
- 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 long-leaved phlomis care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of long-leaved phlomis 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 long-leaved phlomis
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 long-leaved phlomis — frequently asked questions
What fertiliser does long-leaved phlomis 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. Long-Leaved Phlomis 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 long-leaved phlomis?
Apply a single low-nitrogen feed in spring; this species is adapted to infertile soils and over-feeding results in weak, floppy stems that are prone to wind and frost damage. Apply a single low-nitrogen feed in spring; this species is adapted to infertile soils and over-feeding results in weak, floppy stems that are prone to wind and frost damage. 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 long-leaved phlomis?
Half strength is the safe default for long-leaved phlomis — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding long-leaved phlomis 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 long-leaved phlomis 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 long-leaved phlomis?
Flush the pot of long-leaved phlomis 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
- Long-Leaved Phlomis care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water long-leaved phlomis — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
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- All 10153 fertilising guides in the Growli library