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Fertilising guide

How to fertilise Red amaranth (Amaranthus cruentus)— schedule & NPK

Also called Red amaranth, Purple amaranth, Blood amaranth, African spinach.

More about red amaranth

About Red amaranth

Amaranthus cruentus · also called Red amaranth, Purple amaranth · flowering

Red amaranth is a vigorous, heat-loving annual grown for both its dramatic plum-red or crimson flower plumes and its highly nutritious edible leaves and seeds. Tolerant of drought and poor soil, it performs best in full sun with moderate fertility. Its architectural stature makes it a striking border plant and excellent dried flower.

Growth habit: Tall, upright annual with arching terminal and lateral flower plumes

What fertiliser red amaranth actually wants — and why

Red amaranth 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 red amaranth: 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 red amaranth, 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 red amaranth:

One balanced slow-release fertiliser application at planting supports establishment. Additional feeding is rarely needed and may reduce flowering. If grown primarily for edible leaf production, monthly nitrogen-rich feeds will boost yield. 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 red amaranth 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 red amaranth

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

Signs you are over-feeding red amaranth

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

Signs you are under-feeding red amaranth

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

Flushing and leaching the salts

Flush the pot of red amaranth 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 red amaranth

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 red amaranth — frequently asked questions

What fertiliser does red amaranth 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. Red amaranth 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 red amaranth?

One balanced slow-release fertiliser application at planting supports establishment. Additional feeding is rarely needed and may reduce flowering. If grown primarily for edible leaf production, monthly nitrogen-rich feeds will boost yield. One balanced slow-release fertiliser application at planting supports establishment. Additional feeding is rarely needed and may reduce flowering. If grown primarily for edible leaf production, monthly nitrogen-rich feeds will boost yield. 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 red amaranth?

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

What does over-feeding red amaranth 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 red amaranth 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 red amaranth?

Flush the pot of red amaranth 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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