Fertilising guide
How to fertilise Philodendron subhastatum (Philodendron subhastatum)— schedule & NPK
Also called Subhastatum, Red-Back Philodendron.
More about philodendron subhastatum
About Philodendron subhastatum
Philodendron subhastatum · also called Subhastatum, Red-Back Philodendron · houseplant
Philodendron subhastatum is a striking climbing aroid with large, glossy, arrow-shaped leaves that are deep green above and dramatically flushed red to maroon on the undersides. As it climbs and matures, the leaves enlarge and the bicolour effect intensifies. A vigorous, relatively easy grower, it makes a bold statement on a moss pole in bright, humid conditions.
Growth habit: Climbing vine; scrambles upward on support, producing progressively larger arrow-shaped leaves with deepening red undersides as it matures.
Watch for — Brown leaf tips: Low humidity or salt buildup. Raise humidity above 60% and flush the soil periodically.
What fertiliser philodendron subhastatum actually wants — and why
Philodendron subhastatum is a genuinely hungry tropical — in bright warmth it pushes growth fast and rewards a regular half-strength balanced feed all season.
A balanced liquid feed (even N-P-K) or a slightly nitrogen-leaning foliage feed — this is a big-leaved foliage plant putting on real size, so it wants steady nitrogen for lush leaves, not a bloom 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 philodendron subhastatum: 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 philodendron subhastatum, 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 philodendron subhastatum:
Feed monthly in spring and summer with a balanced liquid fertiliser at half strength to support its fast climbing growth. Reduce in autumn and pause in winter. Flush the soil occasionally to clear accumulated fertiliser salts. For a fast grower like this that means feeding regularly — about monthly — right through spring through early autumn (roughly March to September), tapering off only as light drops in autumn.
The dormant-season rule matters more than the exact interval: skip feeding entirely when philodendron subhastatum 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 philodendron subhastatum
Half strength every feed is the sweet spot for philodendron subhastatum: frequent enough to fuel fast growth, dilute enough that it never scorches even when you feed often.
Feeding always goes onto already-damp soil, never dry roots — water philodendron subhastatum first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the philodendron subhastatum watering schedule.
Signs you are over-feeding philodendron subhastatum
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for philodendron subhastatum:
- Brown, scorched leaf tips and margins despite correct watering.
- A white salt crust on the soil or around the pot edge.
- Sudden leaf yellowing and drop shortly after a strong feed.
- Soft, weak, over-stretched growth that cannot support itself.
Signs you are under-feeding philodendron subhastatum
- New leaves coming in noticeably smaller than older ones.
- Pale, yellow-green older leaves and slow growth through peak summer.
- A general loss of vigour and gloss in a plant that should be racing away.
If the symptoms point at watering, light or roots rather than nutrition, the full philodendron subhastatum care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Because you feed often, salts accumulate faster — flush the pot of philodendron subhastatum with plain water until it drains freely roughly every month through the feeding season to keep the root zone clean.
Organic vs synthetic feeds for philodendron subhastatum
Organic options
A diluted seaweed or fish-and-seaweed feed plus a yearly top-dress of worm castings supports fast growth without burn risk. UK: Westland seaweed or Baby Bio Organic; US: Neptune's Harvest or Espoma Indoor!.
Synthetic / liquid feeds
A balanced houseplant liquid at half strength applied frequently — UK: Baby Bio, Phostrogen or Westland Houseplant Feed; US: Miracle-Gro Indoor Plant Food or Dyna-Gro Foliage-Pro for steady leafy growth.
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 philodendron subhastatum — frequently asked questions
What fertiliser does philodendron subhastatum need?
A balanced liquid feed (even N-P-K) or a slightly nitrogen-leaning foliage feed — this is a big-leaved foliage plant putting on real size, so it wants steady nitrogen for lush leaves, not a bloom formula. Philodendron subhastatum is a genuinely hungry tropical — in bright warmth it pushes growth fast and rewards a regular half-strength balanced feed all season.
How often should I feed philodendron subhastatum?
Feed monthly in spring and summer with a balanced liquid fertiliser at half strength to support its fast climbing growth. Reduce in autumn and pause in winter. Flush the soil occasionally to clear accumulated fertiliser salts. Feed monthly in spring and summer with a balanced liquid fertiliser at half strength to support its fast climbing growth. Reduce in autumn and pause in winter. Flush the soil occasionally to clear accumulated fertiliser salts. For a fast grower like this that means feeding regularly — about monthly — right through spring through early autumn (roughly March to September), tapering off only as light drops in autumn.
What strength of feed for philodendron subhastatum?
Half strength every feed is the sweet spot for philodendron subhastatum: frequent enough to fuel fast growth, dilute enough that it never scorches even when you feed often.
What does over-feeding philodendron subhastatum look like?
Brown, scorched leaf tips and margins despite correct watering. A white salt crust on the soil or around the pot edge. Sudden leaf yellowing and drop shortly after a strong feed. Soft, weak, over-stretched growth that cannot support itself. The mistake here is the opposite of most houseplants: under-feeding a fast tropical in peak season starves it, leaving small, pale new leaves and slow growth — but full-strength doses still burn it, so feed often and weak, not occasionally and strong.
Should I flush the soil of philodendron subhastatum?
Because you feed often, salts accumulate faster — flush the pot of philodendron subhastatum with plain water until it drains freely roughly every month through the feeding season to keep the root zone clean.
Keep reading
- Philodendron subhastatum care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water philodendron subhastatum — 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 snake plant
- How to fertilise dracaena
- How to fertilise peperomia
- All 2464 fertilising guides in the Growli library