Fertilising guide
How to fertilise Carob (Ceratonia siliqua)— schedule & NPK
Also called Carob, Locust bean, St John's bread.
More about carob
About Carob
Ceratonia siliqua · also called Carob, Locust bean · tropical
Carob is a tough Mediterranean evergreen tree producing sweet brown pods used as a cocoa substitute and animal feed. Highly drought- and heat-tolerant, it thrives in full sun and poor, free-draining soil, and tolerates coastal and dry conditions. It is frost-tender when young but hardy to light frost once established. Slow-growing, long-lived and often dioecious, needing a male for pods.
Growth habit: Slow-growing, long-lived evergreen tree with a broad domed canopy, dark glossy pinnate leaves and pendent leathery pods; usually dioecious, so both sexes are needed for a pod crop.
What fertiliser carob actually wants — and why
Carob 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 carob: 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 carob, 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 carob:
A low feeder adapted to poor soils; a light application of balanced fertiliser in spring is ample for young trees, and established trees often need none. As a legume it fixes some nitrogen, so avoid high-nitrogen feeds that promote soft, frost-prone growth. 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 carob 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 carob
Half strength is the safe default for carob — 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 carob first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the carob watering schedule.
Signs you are over-feeding carob
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for carob:
- 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 carob
- 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 carob care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of carob 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 carob
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 carob — frequently asked questions
What fertiliser does carob 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. Carob 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 carob?
A low feeder adapted to poor soils; a light application of balanced fertiliser in spring is ample for young trees, and established trees often need none. As a legume it fixes some nitrogen, so avoid high-nitrogen feeds that promote soft, frost-prone growth. A low feeder adapted to poor soils; a light application of balanced fertiliser in spring is ample for young trees, and established trees often need none. As a legume it fixes some nitrogen, so avoid high-nitrogen feeds that promote soft, frost-prone growth. 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 carob?
Half strength is the safe default for carob — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding carob 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 carob 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 carob?
Flush the pot of carob 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
- Carob care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water carob — 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 monstera
- How to fertilise pothos
- How to fertilise fiddle leaf fig
- All 5561 fertilising guides in the Growli library