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Fertilising guide

How to fertilise Purple Fountain Grass (Pennisetum setaceum 'Rubrum')— schedule & NPK

Also called purple fountain grass, red fountain grass.

More about purple fountain grass

About Purple Fountain Grass

Pennisetum setaceum 'Rubrum' · also called purple fountain grass, red fountain grass · flowering

Purple fountain grass is a tender ornamental grass with burgundy-red foliage and arching, foxtail-like purple plumes from summer to frost. It forms a graceful fountain-shaped mound and is grown as an annual or container specimen in cold climates, overwintered only where frost is absent. Heat-loving and sun-hungry, it adds rich colour and movement.

Growth habit: Tender, warm-season clump-forming grass with a fountain-like mound of arching purple foliage and nodding flower spikes; frost-sensitive and treated as an annual or overwintered as a dormant container plant in cold regions.

What fertiliser purple fountain grass actually wants — and why

Purple Fountain Grass 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 purple fountain grass: 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 purple fountain grass, 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 purple fountain grass:

Feed lightly but regularly when grown in containers, every few weeks through summer with a balanced liquid feed, since potting mix is quickly depleted. In-ground plants need only a light spring feed. 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 purple fountain grass 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 purple fountain grass

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

Signs you are over-feeding purple fountain grass

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

Signs you are under-feeding purple fountain grass

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

Flushing and leaching the salts

Flush the pot of purple fountain grass 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 purple fountain grass

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 purple fountain grass — frequently asked questions

What fertiliser does purple fountain grass 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. Purple Fountain Grass 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 purple fountain grass?

Feed lightly but regularly when grown in containers, every few weeks through summer with a balanced liquid feed, since potting mix is quickly depleted. In-ground plants need only a light spring feed. Feed lightly but regularly when grown in containers, every few weeks through summer with a balanced liquid feed, since potting mix is quickly depleted. In-ground plants need only a light spring feed. 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 purple fountain grass?

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

What does over-feeding purple fountain grass 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 purple fountain grass 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 purple fountain grass?

Flush the pot of purple fountain grass 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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