Red amaranth (Purple amaranth) care

Light

Red amaranth needs sun on the leaves, not just bright ambient room light. Demands full sun — at least 6 hours daily. Full sun produces the most vivid red colouring in foliage and plumes. Shade causes pale, unhealthy plants that rarely reach mature height. A south or west-facing windowsill in the northern hemisphere is the default; anywhere else, expect the plant to stretch and pale out within a season.

Watering

Water red amaranth every 7–10 days once established. The actual day count varies with pot size, light, and season — the finger test (or lifting the pot to feel its weight) is more reliable than a fixed calendar. Empty any drainage saucer afterwards so the pot isn't sitting in water. Deeply drought-tolerant once established, but young seedlings require consistent moisture. Water at the base. Established plants can withstand dry spells but produce the best plume development with moderate, regular irrigation.

Soil and pot

Red amaranth grows best in well-drained loam to sandy loam, ph 6.0–7.5. Adaptable to poor and moderately fertile soils. Overly rich soil encourages excessive vegetative growth at the expense of flower-plume production. Good drainage is essential; waterlogging is fatal. A pot with a working drainage hole is non-negotiable for this species — even free-draining mix will turn soggy in a closed planter. If you love the look of a decorative pot without a hole, use it as a cachepot around an inner nursery pot you can lift out to water.

Humidity and temperature

Red amaranth sits happiest at around 30–70% humidity and 18–35°C (64–95°F). Highly adaptable to a wide humidity range. Naturally at home in semi-arid and tropical/subtropical climates. Excellent air circulation prevents the minor fungal issues that can arise in cool, damp summers. If you keep the room above 18–35°C year-round and avoid placing the plant near a cold draught, a hot radiator, or an air-conditioning vent, you have already handled the two biggest indoor stressors.

Fertilising

Feed red amaranth sparingly. 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. Skip fertiliser entirely on a stressed, recently-repotted, or actively wilting plant — fertiliser salts make damage worse, not better. Wait for a round of healthy new growth before resuming a feeding rhythm.

Common problems

Below are the issues we see most often on red amaranth in the Growli community. Each is annotated with the most common cause so you know where to start.

• Aphid infestations — Dense colonies of black or green aphids, especially on new growth and flower plumes. Blast off with a strong jet of water or apply insecticidal soap. Companion-plant with nasturtium as a trap crop.
• Damping-off in seedlings — Young seedlings collapse at soil level in cold, wet, or poorly ventilated conditions. Sow in warm (21°C+) well-drained compost. Avoid overwatering and provide good air circulation during germination.
• Cercospora leaf spot — Circular brown or tan spots with darker margins on older leaves, caused by Cercospora fungal species. Remove affected foliage, improve airflow, and rotate planting sites. Generally not fatal to established plants.

Propagation

Direct-sow into warm soil (18°C+) after last frost, pressing seeds onto the surface (light-requiring germinator). Thin to 45–60 cm. Can be started indoors 4–6 weeks before last frost. Self-seeds prolifically — deadhead if volunteers are unwanted. Seed is also harvested for grain use at end of season. Propagation is the cheapest, most satisfying way to expand a collection — and it doubles as insurance against losing a mature plant to an accident. Take a backup cutting once the parent is established and healthy.

Toxicity to pets

Red amaranth is mildly toxic to pets. Amaranthus cruentus leaves are edible and widely consumed by humans. However, the ASPCA lists Amaranthus retroflexus (pigweed, a closely related species) as toxic to cats and dogs (causes tremors, nephrotoxicity). Out of caution, Amaranthus cruentus should be kept away from pets; the full safety profile for this specific species is not individually confirmed as non-toxic by the ASPCA. If you keep cats, dogs, or curious children in the house, weigh placement carefully — a high shelf or a hanging planter is enough for casual safety. For severe ingestion incidents, call your local vet and the ASPCA Animal Poison Control Center (in the US, 888-426-4435).

Pet-safety status is sourced from the ASPCA Toxic and Non-Toxic Plant List, which catalogues the most-asked-about plants for cats, dogs, and horses.

Red amaranth deep-dive guides

Every aspect of red amaranth care, each with its own calibrated guide:

• Common red amaranth problems & fixes
• Red amaranth watering schedule
• Red amaranth light requirements
• Best soil mix for red amaranth
• Red amaranth fertilizing guide
• When to repot red amaranth
• How to propagate red amaranth
• How to prune red amaranth
• What's eating my red amaranth?
• Red amaranth growth rate & size
• Red amaranth cold hardiness
• Red amaranth temperature & humidity
• Is red amaranth toxic to cats & dogs?
• Is red amaranth toxic to cats?
• Is red amaranth toxic to dogs?
• Getting red amaranth to bloom

Featured in these plant shortlists

Red amaranth qualifies for 4 curated Growli shortlists — each one filtered objectively from our structured plant-care library, so the selection is consistent and checkable:

• Best drought-tolerant houseplants — Houseplants that prefer to dry out — forgiving of forgotten watering and ideal for travel or busy weeks.
• Best flowering houseplants — Indoor plants grown for their blooms — selected from the flowering species in Growli’s plant-care library.
• Best houseplants for full sun — Houseplants that want direct sun — the species for a hot south or west-facing windowsill where shade-lovers scorch.
• Best fast-growing houseplants — Houseplants documented as fast or vigorous growers — quick to fill a pot, cover a pole or trail down a shelf.
• Browse all 29 plant shortlists — pet-safe, low-light, drought-tolerant and more

Related guides

Red amaranth is also known as Red amaranth, Purple amaranth, Blood amaranth, and African spinach.

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