Fertilising guide
How to fertilise Black-Eyed Susan Vine (Thunbergia alata)— schedule & NPK
Also called Black-Eyed Susan, Clockvine, Thunbergia.
More about black-eyed susan vine
About Black-Eyed Susan Vine
Thunbergia alata · also called Black-Eyed Susan, Clockvine · tropical
Thunbergia alata is a cheerful twining annual or tender perennial vine from tropical Africa, bearing masses of orange, yellow, or cream flowers with a striking dark brown-black centre. It is fast-growing and ideal for containers, hanging baskets, and trellises. Considered pet-safe by the ASPCA, making it a family-friendly choice.
Growth habit: Twining annual or tender perennial vine
Watch for — Poor flowering: Usually caused by low light or over-rich soil; move to a sunnier spot and avoid excess nitrogen.
What fertiliser black-eyed susan vine actually wants — and why
Black-Eyed Susan Vine 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 black-eyed susan vine: 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 black-eyed susan vine, 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 black-eyed susan vine:
Feed with a balanced liquid fertiliser at half strength every two weeks during spring and summer. A slightly higher potassium ratio supports prolific flowering. Stop feeding in autumn as growth naturally slows. 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 black-eyed susan vine 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 black-eyed susan vine
Half strength is the safe default for black-eyed susan vine — 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 black-eyed susan vine first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the black-eyed susan vine watering schedule.
Signs you are over-feeding black-eyed susan vine
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for black-eyed susan vine:
- 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 black-eyed susan vine
- 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 black-eyed susan vine care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of black-eyed susan vine 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 black-eyed susan vine
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 black-eyed susan vine — frequently asked questions
What fertiliser does black-eyed susan vine 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. Black-Eyed Susan Vine 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 black-eyed susan vine?
Feed with a balanced liquid fertiliser at half strength every two weeks during spring and summer. A slightly higher potassium ratio supports prolific flowering. Stop feeding in autumn as growth naturally slows. Feed with a balanced liquid fertiliser at half strength every two weeks during spring and summer. A slightly higher potassium ratio supports prolific flowering. Stop feeding in autumn as growth naturally slows. 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 black-eyed susan vine?
Half strength is the safe default for black-eyed susan vine — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding black-eyed susan vine 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 black-eyed susan vine 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 black-eyed susan vine?
Flush the pot of black-eyed susan vine 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
- Black-Eyed Susan Vine care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water black-eyed susan vine — 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 brush cherry
- How to fertilise araza
- How to fertilise uvaia
- All 11687 fertilising guides in the Growli library