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Light requirements

How much light does Yarrow (Achillea millefolium) need?

Also called yarrow, common yarrow, milfoil.

More about yarrow

About Yarrow

Achillea millefolium · also called yarrow, common yarrow · herb

Yarrow is a tough, drought-resistant perennial with finely divided ferny leaves and flat-topped clusters of tiny flowers from summer into autumn. A magnet for pollinators and beneficial insects, it spreads by rhizomes to form weed-suppressing mats. Ideal for dry meadows and gravel gardens, it is toxic to pets and grazing animals if eaten.

Comfort temperature: -30 to 30°C

Watch for — Flopping stems: Tall cultivars splay open in rich soil or shade; grow lean and sunny, or support, and cut back after first flowering for sturdier regrowth.

The exact light yarrow needs

Yarrow is a sun-driven crop — yield is directly limited by how much direct sun it gets, so this is one plant where "more light, more harvest" is literally true.

Put a number on it — this is what a meter (or a free phone light-meter app) should read where yarrow sits:

In plain terms, Full sun outdoors: an open spot that gets 6–8 hours of unobstructed direct sun, ideally including midday. Indoors or on a windowsill it needs the brightest south-facing position you have and usually still benefits from a grow light. Shaded beds, north-facing walls, and gappy "dappled" light — these grow lush leaves but little or poor-quality crop.

Not sure how to read the light in your home? Our light meter guide walks through measuring footcandles and lux with a free phone app and turning the reading into a placement decision for yarrow.

Signs yarrow is getting too much light

The most exposed leaves show it first. For yarrow specifically, watch for:

Light damage does not heal — a scorched leaf stays scorched — so the fix is to move yarrow out of the harsh light rather than wait for it to recover.

Signs yarrow is not getting enough light

Too little light is slower and sneakier than too much. The classic tell is etiolation: the plant stretches and pales as it reaches for a window. For yarrow, look for:

If yarrow is stretched, leggy and pale, our guide to leggy, stretched plants covers how to fix it and whether it can be pruned back into shape. Tucking yarrow into a part-shade corner and expecting a full crop. Leafy growth tolerates some shade, but fruit, roots and flavour are paid for in hours of direct sun — short the light and you short the harvest.

Where to put yarrow: the best window and room

Give yarrow the sunniest open ground or the largest container in the brightest spot you have. A south-facing wall, allotment in the open, or unshaded raised bed is ideal. If you are growing it indoors or on a balcony, a full-spectrum grow light is usually not optional but essential — a windowsill alone rarely ripens a sun crop well.

  1. Pick the sunniest position. Site yarrow where it gets 6–8 hours of direct sun — open ground or the brightest container spot, away from walls and tree shade.
  2. Track the sun across the season. A spot sunny in May can be shaded by a leafed-out tree or low autumn sun later. Watch where the shadows actually fall before committing.
  3. Add a grow light indoors. Growing yarrow inside or on a windowsill? Run a strong full-spectrum LED 12–16 hours a day — windowsill light alone rarely crops well.
  4. Mulch and water to handle the heat. Full sun comes with heat stress; mulch and consistent watering prevent the scorch and bolting that sun gets blamed for.

Does yarrow need a grow light?

For indoor or windowsill growing, yarrow almost always needs a grow light to crop properly: a strong full-spectrum LED run 12–16 hours a day, positioned close. Light is the single biggest limiting factor for a sun crop grown inside — soil and water can be perfect and it will still fail in dim light.

The seasonal light shift (why winter changes everything)

Yarrow is a growing-season crop. Outdoors, plant it so its main growth lands in the long, high-sun months — light and warmth fall away fast from autumn. For year-round indoor growing you must replace the lost winter sun with a grow light on a timer; the natural window light from October to February is far too weak for cropping.

Light and watering are linked: a plant in weaker winter light photosynthesises and drinks far less, so the same routine that worked in summer can rot it. See how often to water yarrow for the season-by-season schedule that pairs with this light plan.

Yarrow light requirements — frequently asked questions

How much light does yarrow need?

Yarrow needs Outdoor full sun is ~5,000–10,000+ fc; far beyond anything a windowsill provides. Tens of thousands of lux in open sun — orders of magnitude more than typical indoor light. Full sun outdoors: an open spot that gets 6–8 hours of unobstructed direct sun, ideally including midday. Indoors or on a windowsill it needs the brightest south-facing position you have and usually still benefits from a grow light.

Can yarrow survive in low light?

No, not really. Yarrow is a sun lover — in low light it etiolates: it stretches, pales, weakens and slows right down. It will not instantly die, but it steadily declines and never looks its best.

What are the signs yarrow is getting too much light?

In extreme heat plus intense sun, leaf scorch or sunscald on exposed fruit — usually a heat/water-stress combination rather than light alone; mulch and steady watering fix most of it. Wilting in the fiercest afternoon sun that recovers by evening — yarrow is photosynthesising hard, not over-lit; keep it watered. Bolting (premature flowering) in leafy crops is triggered more by heat and daylength than raw light intensity. Tucking yarrow into a part-shade corner and expecting a full crop. Leafy growth tolerates some shade, but fruit, roots and flavour are paid for in hours of direct sun — short the light and you short the harvest.

What are the signs yarrow is not getting enough light?

Tall, pale, leggy, floppy yarrow reaching for the light, with thin stems that flop — classic shade etiolation. Poor flowering and a small, late, disappointing or non-existent harvest — the clearest sign it is under-lit. Lush dark leaves but few fruit; soft growth that pests and disease find easily. If you see this, move yarrow closer to the light or add a grow light — and check our guide on leggy, stretched plants.

Does yarrow need a grow light?

For indoor or windowsill growing, yarrow almost always needs a grow light to crop properly: a strong full-spectrum LED run 12–16 hours a day, positioned close. Light is the single biggest limiting factor for a sun crop grown inside — soil and water can be perfect and it will still fail in dim light.

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