Fertilising guide
How to fertilise Nettle-leaved Mullein (Verbascum chaixii)— schedule & NPK
Also called Nettle-leaved Mullein, Chaix's Mullein, Chaixii Mullein.
More about nettle-leaved mullein
About Nettle-leaved Mullein
Verbascum chaixii · also called Nettle-leaved Mullein, Chaix's Mullein · flowering
Nettle-leaved Mullein is an elegant perennial mullein from central and southern Europe, valued for its tall, branched spikes of yellow (or white in 'Album') flowers with violet-purple stamens. Unlike most mulleins it persists reliably for several years, making it a dependable cottage-garden perennial. It is drought-tolerant and an excellent pollinator plant.
Growth habit: Clump-forming perennial with basal rosette; erect branched flowering stems arising each summer
What fertiliser nettle-leaved mullein actually wants — and why
Nettle-leaved Mullein 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 nettle-leaved mullein: 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 nettle-leaved mullein, 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 nettle-leaved mullein:
Minimal. An annual top-dressing of low-nitrogen fertiliser (e.g. bonemeal or 5-10-10) in early spring is adequate. Avoid high nitrogen, which produces soft, floppy growth prone to flopping. 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 nettle-leaved mullein 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 nettle-leaved mullein
Half strength is the safe default for nettle-leaved mullein — 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 nettle-leaved mullein first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the nettle-leaved mullein watering schedule.
Signs you are over-feeding nettle-leaved mullein
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for nettle-leaved mullein:
- 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 nettle-leaved mullein
- 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 nettle-leaved mullein care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of nettle-leaved mullein 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 nettle-leaved mullein
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 nettle-leaved mullein — frequently asked questions
What fertiliser does nettle-leaved mullein 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. Nettle-leaved Mullein 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 nettle-leaved mullein?
Minimal. An annual top-dressing of low-nitrogen fertiliser (e.g. bonemeal or 5-10-10) in early spring is adequate. Avoid high nitrogen, which produces soft, floppy growth prone to flopping. Minimal. An annual top-dressing of low-nitrogen fertiliser (e.g. bonemeal or 5-10-10) in early spring is adequate. Avoid high nitrogen, which produces soft, floppy growth prone to flopping. 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 nettle-leaved mullein?
Half strength is the safe default for nettle-leaved mullein — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding nettle-leaved mullein 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 nettle-leaved mullein 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 nettle-leaved mullein?
Flush the pot of nettle-leaved mullein 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
- Nettle-leaved Mullein care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water nettle-leaved mullein — 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 pineleaf penstemon
- How to fertilise eaton's firecracker
- How to fertilise front range beardtongue
- All 8452 fertilising guides in the Growli library