Fertilising guide
How to fertilise Slack's Sundew (Drosera slackii)— schedule & NPK
Also called Slack's sundew.
More about slack's sundew
About Slack's Sundew
Drosera slackii · also called Slack's sundew · houseplant
Drosera slackii is a large, rosette-forming sundew endemic to a small area of the Western Cape, South Africa, named in honour of renowned carnivorous plant author Adrian Slack. It forms impressive rosettes of long, paddle-shaped leaves densely covered in red tentacles, making it one of the most visually striking of the African sundews for windowsill cultivation.
Growth habit: Large, rosette-forming perennial producing a flat to slightly ascending rosette. Leaves are long (up to 12 cm) and spoon-shaped (spatulate), held on distinct petioles. The lamina is densely packed with bright-red glandular tentacles. Produces upright scapes bearing white flowers.
Watch for — Green, pale leaves with little mucilage: Indicates insufficient light. Move to a sunnier position or add supplemental grow lighting. D. slackii produces its characteristic deep red colour and generous mucilage only in strong, direct light.
What fertiliser slack's sundew actually wants — and why
Slack's Sundew 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 slack's sundew: 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 slack's sundew, 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 slack's sundew:
Do not add fertiliser to substrate. Supplement with small live insects (fruit flies, springtails, small mosquitoes) or tiny pieces of freeze-dried bloodworm placed on the leaf tentacles monthly during active growth if natural prey is unavailable. Do not overfeed — one or two leaves at a time is sufficient. Treat that as monthly 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 slack's sundew 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 slack's sundew
Half strength is the safe default for slack's sundew — 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 slack's sundew first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the slack's sundew watering schedule.
Signs you are over-feeding slack's sundew
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for slack's sundew:
- 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 slack's sundew
- 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 slack's sundew care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of slack's sundew 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 slack's sundew
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 slack's sundew — frequently asked questions
What fertiliser does slack's sundew 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. Slack's Sundew 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 slack's sundew?
Do not add fertiliser to substrate. Supplement with small live insects (fruit flies, springtails, small mosquitoes) or tiny pieces of freeze-dried bloodworm placed on the leaf tentacles monthly during active growth if natural prey is unavailable. Do not overfeed — one or two leaves at a time is sufficient. Do not add fertiliser to substrate. Supplement with small live insects (fruit flies, springtails, small mosquitoes) or tiny pieces of freeze-dried bloodworm placed on the leaf tentacles monthly during active growth if natural prey is unavailable. Do not overfeed — one or two leaves at a time is sufficient. Treat that as monthly 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 slack's sundew?
Half strength is the safe default for slack's sundew — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding slack's sundew 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 slack's sundew 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 slack's sundew?
Flush the pot of slack's sundew 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
- Slack's Sundew care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water slack's sundew — 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 hound's tongue fern
- How to fertilise pinstripe calathea
- How to fertilise peacock plant
- All 6887 fertilising guides in the Growli library