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Fertilising guide

How to fertilise Cape Sundew (Drosera capensis)— schedule & NPK

Also called Cape sundew, Cape rainbow plant.

More about cape sundew

About Cape Sundew

Drosera capensis · also called Cape sundew, Cape rainbow plant · houseplant

Drosera capensis is a subtropical carnivorous perennial native to the Cape region of South Africa, where it grows in open, nutrient-poor, moist peaty ground in full sun. It is one of the easiest carnivorous plants to grow, producing rosettes of strap-shaped leaves densely studded with red, gland-tipped tentacles that trap, curl around, and digest small insects. The key rule is to use only mineral-free water (rainwater, distilled, or reverse-osmosis) — tap water mineral build-up will kill it within months. Non-toxic to pets according to carnivorous plant specialist authorities; the ASPCA has not individually listed the species, so 'mildly-toxic' is applied as a precautionary classification.

Growth habit: Clump-forming, rosette-producing subtropical perennial; stems elongate with age and the plant self-seeds prolifically where conditions allow.

Watch for — Tentacle loss and leaf blackening from tap water: Dissolved minerals and chlorine in tap water accumulate rapidly in the nutrient-sensitive root zone; even brief use can cause tentacle dieback and root damage. Switch immediately to rainwater or distilled water and flush the medium with several volumes of mineral-free water.

What fertiliser cape sundew actually wants — and why

Cape 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 cape 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 cape 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 cape sundew:

Never apply soil or foliar fertiliser — the plant obtains all nutrients from captured insects. Indoors where insects are scarce, place one small live or dried fly per leaf trap every 2–4 weeks during the growing season. 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 cape 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 cape sundew

Half strength is the safe default for cape 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 cape sundew first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the cape sundew watering schedule.

Signs you are over-feeding cape sundew

Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for cape sundew:

Signs you are under-feeding cape sundew

If the symptoms point at watering, light or roots rather than nutrition, the full cape sundew care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

Flush the pot of cape 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 cape 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 cape sundew — frequently asked questions

What fertiliser does cape 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. Cape 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 cape sundew?

Never apply soil or foliar fertiliser — the plant obtains all nutrients from captured insects. Indoors where insects are scarce, place one small live or dried fly per leaf trap every 2–4 weeks during the growing season. Never apply soil or foliar fertiliser — the plant obtains all nutrients from captured insects. Indoors where insects are scarce, place one small live or dried fly per leaf trap every 2–4 weeks during the growing season. 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 cape sundew?

Half strength is the safe default for cape sundew — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.

What does over-feeding cape 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 cape 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 cape sundew?

Flush the pot of cape 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.

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