Growli
Let's go

Fertilising guide

How to fertilise Merrill's Wax Plant (Hoya merrillii)— schedule & NPK

Also called Merrill's wax plant, Merrill's hoya, Philippine wax plant.

More about merrill's wax plant

About Merrill's Wax Plant

Hoya merrillii · also called Merrill's wax plant, Merrill's hoya · tropical

Hoya merrillii is a rare epiphytic vine native to the Philippines, first discovered in humid lowland forests on Mindoro Island, and named in honour of American botanist Elmer Drew Merrill who extensively documented Philippine flora. It is prized for its compact umbels of up to 25 small, star-shaped, golden-yellow flowers with red-orange centres that emit a sweet, honey-and-caramel fragrance most intense in the evenings. The most important care point is to provide warm temperatures with high humidity and avoid cold draughts, as it cannot tolerate temperatures below 15°C for any length of time. The ASPCA lists the Hoya genus as non-toxic to cats and dogs.

Growth habit: Climbing or trailing epiphytic vine with oval to elliptical, glossy, waxy leaves reaching 10–15 cm; new leaves emerge with a light bronze tint.

What fertiliser merrill's wax plant actually wants — and why

Merrill's Wax Plant 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 merrill's wax plant: 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 merrill's wax plant, 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 merrill's wax plant:

Feed monthly in spring and summer with a half-strength balanced liquid fertiliser; switching to a low-nitrogen, high-potassium feed in late summer can help promote flowering. 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 merrill's wax plant 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 merrill's wax plant

Half strength is the safe default for merrill's wax plant — 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 merrill's wax plant first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the merrill's wax plant watering schedule.

Signs you are over-feeding merrill's wax plant

Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for merrill's wax plant:

Signs you are under-feeding merrill's wax plant

If the symptoms point at watering, light or roots rather than nutrition, the full merrill's wax plant care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

Flush the pot of merrill's wax plant 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 merrill's wax plant

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 merrill's wax plant — frequently asked questions

What fertiliser does merrill's wax plant 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. Merrill's Wax Plant 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 merrill's wax plant?

Feed monthly in spring and summer with a half-strength balanced liquid fertiliser; switching to a low-nitrogen, high-potassium feed in late summer can help promote flowering. Feed monthly in spring and summer with a half-strength balanced liquid fertiliser; switching to a low-nitrogen, high-potassium feed in late summer can help promote flowering. 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 merrill's wax plant?

Half strength is the safe default for merrill's wax plant — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.

What does over-feeding merrill's wax plant 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 merrill's wax plant 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 merrill's wax plant?

Flush the pot of merrill's wax plant 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