Fertilising guide
How to fertilise Summer Hyacinth (Galtonia candicans)— schedule & NPK
Also called Summer Hyacinth, Spire Lily, Cape Hyacinth.
More about summer hyacinth
About Summer Hyacinth
Galtonia candicans · also called Summer Hyacinth, Spire Lily · flowering
Galtonia candicans is a stately South African bulbous perennial bearing tall spikes of pendant, fragrant, bell-shaped white flowers in mid to late summer, naturalising well in sunny mixed borders. It is best grown in full sun in fertile, moisture-retentive but well-drained soil, and in colder UK gardens (below RHS H4 regions) bulbs should be mulched deeply or lifted for winter. The most important care point is to ensure adequate summer moisture during the growing season while maintaining good drainage to prevent winter rot. The ASPCA specifically lists Galtonia (Summer Hyacinth) as non-toxic to cats, dogs, and horses.
Growth habit: Clump-forming bulbous perennial; self-naturalises in suitable conditions
What fertiliser summer hyacinth actually wants — and why
Summer Hyacinth feeds for next year, not this one — the critical window is after flowering, while the leaves are still green and recharging the bulb.
A low-nitrogen, potassium- and phosphorus-leaning bulb fertiliser (something like 5-10-10) or bonemeal at planting. High nitrogen grows floppy leaves and rots stored bulbs.
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 summer hyacinth: 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 summer hyacinth, 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 summer hyacinth:
Apply a balanced granular fertiliser at planting in spring; supplement with a high-potassium liquid feed every 2–3 weeks during the growing season to support tall spike development. The rhythm: a bulb feed at planting, a light feed as leaves emerge, and — most important — a potassium feed straight after flowering while the foliage is still green and feeding the bulb. Never cut the leaves off early.
The dormant-season rule matters more than the exact interval: skip feeding entirely when summer hyacinth 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 summer hyacinth
Use the bulb-feed label rate for summer hyacinth; the timing (post-bloom, leaves still green) does far more for next year's display than the concentration.
Feeding always goes onto already-damp soil, never dry roots — water summer hyacinth first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the summer hyacinth watering schedule.
Signs you are over-feeding summer hyacinth
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for summer hyacinth:
- Tall, floppy, soft leaves that flop over (too much nitrogen).
- Soft or rotting bulbs lifted at the end of the season.
- Lush foliage but few or poor flowers.
Signs you are under-feeding summer hyacinth
- Progressively fewer or smaller flowers year on year ("going blind").
- Small, weak bulbs and thin foliage.
- Bulbs that fail to come back at all after a few seasons.
If the symptoms point at watering, light or roots rather than nutrition, the full summer hyacinth care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Bulbs are not container-flushed like houseplants; the equivalent is not over-feeding and lifting/dividing congested clumps of summer hyacinth every few years so they are not competing for nutrients.
Organic vs synthetic feeds for summer hyacinth
Organic options
Bonemeal worked in at planting plus a mulch of garden compost or well-rotted leaf-mould is the traditional, reliable approach for summer hyacinth. UK: blood, fish & bone or Westland Bulb Food; US: Espoma Bulb-tone or bonemeal.
Synthetic / liquid feeds
A proprietary bulb fertiliser at planting and a high-potash liquid (tomato feed) after flowering — UK: Westland Bulb Food then Tomorite; US: Miracle-Gro Shake 'n Feed Bulb or a bloom booster post-flower.
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 summer hyacinth — frequently asked questions
What fertiliser does summer hyacinth need?
A low-nitrogen, potassium- and phosphorus-leaning bulb fertiliser (something like 5-10-10) or bonemeal at planting. High nitrogen grows floppy leaves and rots stored bulbs. Summer Hyacinth feeds for next year, not this one — the critical window is after flowering, while the leaves are still green and recharging the bulb.
How often should I feed summer hyacinth?
Apply a balanced granular fertiliser at planting in spring; supplement with a high-potassium liquid feed every 2–3 weeks during the growing season to support tall spike development. Apply a balanced granular fertiliser at planting in spring; supplement with a high-potassium liquid feed every 2–3 weeks during the growing season to support tall spike development. The rhythm: a bulb feed at planting, a light feed as leaves emerge, and — most important — a potassium feed straight after flowering while the foliage is still green and feeding the bulb. Never cut the leaves off early.
What strength of feed for summer hyacinth?
Use the bulb-feed label rate for summer hyacinth; the timing (post-bloom, leaves still green) does far more for next year's display than the concentration.
What does over-feeding summer hyacinth look like?
Tall, floppy, soft leaves that flop over (too much nitrogen). Soft or rotting bulbs lifted at the end of the season. Lush foliage but few or poor flowers. Cutting or tying off the leaves of summer hyacinth as soon as the flowers fade is the great bulb mistake — the bulb recharges through those leaves for weeks afterward, and removing them early means a weak or blind display next year.
Should I flush the soil of summer hyacinth?
Bulbs are not container-flushed like houseplants; the equivalent is not over-feeding and lifting/dividing congested clumps of summer hyacinth every few years so they are not competing for nutrients.
Keep reading
- Summer Hyacinth care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water summer hyacinth — 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 diascia 'wink coral pink'
- How to fertilise nemesia strumosa 'poetry blue'
- How to fertilise nemesia 'sunsatia cranberry'
- All 10153 fertilising guides in the Growli library