How often to water fern leaf yarrow in California
In July in the Central Valley, established fern leaf yarrow in loam needs a deep watering about every 14 days: about 1.5 gallons each time for a plant 2 feet across, about 0.8 gallons a week. Fern leaf yarrow forms a basal clump of finely divided, spicy-scented green leaves. Stiff stems 3 to 4 feet tall rise above it, topped with flat golden yellow flower heads up to 4 inches across. It blooms most of the summer if deadheaded, and the flowers dry well. It tolerates heat and drought, and overwatering is what kills it.
How often to water fern leaf yarrow, month by month
Type your city above and the days between waterings and the gallons appear here, worked out from your city's climate table. Or read the figures by climate zone further down.
How this is worked out: established roots fill the top 1 foot of soil, and you water again when that soil has dried halfway. Loam soil holds about 1.5 inches of water per foot. Water the whole area the plant covers, and skip a watering after a good soaking rain.
How to tell it needs water
- A clump with soil gone dry 4 inches below the surface in summer is ready for a deep drink
- Ferny leaves going limp and gray green in a long hot spell can indicate thirst
- Tall stems flopping over after rich soil and frequent water point to too much of both
- Yellowing leaves and a soft, dark crown in wet soil suggest root rot from overwatering
How to water it
- Water at the base of the clump with drip or a slow hose
- Soak several inches down, then let the soil dry well before watering again
- Plant in full sun in average, well-drained soil, sheltered from strong wind
- Skip fertilizer, which makes stems weak and floppy
- Divide clumps every few years to prevent crowding
Through the seasons
Water a new plant regularly until it is growing well, then switch to deep, infrequent soaks. Established clumps tolerate heat and drought, and too much water or fertilizer makes stems flop and roots rot. Flowers appear most of the summer with deadheading. Winter rain usually covers the cool months near the coast and in the valley. In all four western regions, from the north-central coast and the Central Valley to the south coast and South Inland, WUCOLS gives fern leaf yarrow a low water rating. The two deserts have not been evaluated.
In pots
Fern leaf yarrow can grow in a deep, heavy pot that keeps its tall stems upright. Use a gritty, well-drained mix and water once the top couple of inches have dried, letting water flow out freely. In summer heat, check every few days. Empty the saucer. Deadhead to keep flowers coming and cut stems to the leaves after bloom. In winter, water only when the mix is dry.
- A year
- 6.84 gal per sq ft
- Reference
- Sacramento climate table
- Counts
- Plant need, before sprinkler losses
Monthly water need by climate zone
Fern Leaf Yarrow: gallons per square foot per month, by WUCOLS climate zone
| Month | N. Coast | C. Valley | S. Coast | S. Inland | Hi Desert | Lo Desert |
|---|---|---|---|---|---|---|
| Jan | 0.15 | 0.16 | 0.31 | 0.31 | – | – |
| Feb | 0.21 | 0.26 | 0.32 | 0.35 | – | – |
| Mar | 0.35 | 0.43 | 0.46 | 0.52 | – | – |
| Apr | 0.47 | 0.61 | 0.56 | 0.64 | – | – |
| May | 0.58 | 0.83 | 0.64 | 0.78 | – | – |
| Jun | 0.64 | 0.99 | 0.69 | 0.92 | – | – |
| Jul | 0.64 | 1.07 | 0.79 | 1 | – | – |
| Aug | 0.6 | 0.95 | 0.74 | 0.93 | – | – |
| Sep | 0.5 | 0.72 | 0.6 | 0.74 | – | – |
| Oct | 0.35 | 0.47 | 0.46 | 0.53 | – | – |
| Nov | 0.19 | 0.22 | 0.33 | 0.36 | – | – |
| Dec | 0.12 | 0.14 | 0.26 | 0.27 | – | – |
| Year | 4.8 | 6.84 | 6.2 | 7.37 | – | – |
How this is worked out: the WUCOLS water rating for each zone times that zone’s climate for the month. A dash means WUCOLS does not rate the plant there. The figures are what the plant uses, before sprinkler losses.
Plants with the same water needs 16
Rated low water in the Central Valley, like fern leaf yarrow. Plants that drink alike can share one valve and one schedule.
AgapanthusAgapanthus orientalislow water, Central Valley1.07 gal/sq ft in July
GeraniumsPelargonium x hortorum and cvs.low water, Central Valley1.07 gal/sq ft in July
SalviaSalvia greggii ssp., cvs. & hybridslow water, Central Valley1.07 gal/sq ft in July
IrisesIris germanicalow water, Central Valley1.07 gal/sq ft in July
SucculentsEcheveria spp. & cvs.low water, Central Valley1.07 gal/sq ft in July
Russian SagePerovskia spp. & cvs.low water, Central Valley1.07 gal/sq ft in July
YarrowAchillea millefolium (non-native hybrids)low water, Central Valley1.07 gal/sq ft in July
Mountain AlyssumAlyssum montanumlow water, Central Valley1.07 gal/sq ft in July
Silver SageSalvia argentealow water, Central Valley1.07 gal/sq ft in July
Purple MulleinVerbascum phoeniceumlow water, Central Valley1.07 gal/sq ft in July
Silvery YarrowAchillea clavennaelow water, Central Valley1.07 gal/sq ft in July
California Native YarrowAchillea millefolium (CA native cultivars)low water, Central Valley1.07 gal/sq ft in July
Woolly YarrowAchillea tomentosalow water, Central Valley1.07 gal/sq ft in July
Perennial HollyhockAlcea rosea cvs.low water, Central Valley1.07 gal/sq ft in July
Mountain Lady's MantleAlchemilla alpinalow water, Central Valley1.07 gal/sq ft in July
Lady's MantleAlchemilla mollislow water, Central Valley1.07 gal/sq ft in JulyTurn this into minutes on your water days
Every city page has a calculator that takes fern leaf yarrow, your sprinkler type and the month, and gives the minutes per water day for that supplier's schedule. Or put it in a zone of the personal watering plan and get all twelve months printed.
Questions people ask
How often should I water fern leaf yarrow in summer?
In July, established fern leaf yarrow in loam needs a deep watering about every 14 days in the Central Valley, about every 18 days on the south coast and about every 14 days in the South Inland zone. Sandy soil holds less water, so waterings come closer together. Clay stretches them. Check the soil before each watering and skip one after a soaking rain.
How much water does fern leaf yarrow need per day?
In July in the Central Valley, established fern leaf yarrow needs about 0.1 gallons a day for a plant 2 feet across and about 0.4 gallons a day for a plant 4 feet across. Give it in deep waterings spread days apart rather than a little every day, so the whole root zone gets wet.
Does watering for fern leaf yarrow change across California?
Yes. WUCOLS rates fern leaf yarrow separately for each of the six California climate zones: low water in the North-Central Coastal zone, low water in the Central Valley zone, low water in the South Coastal zone, low water in the South Inland zone, not evaluated in the High and Intermediate Desert zone, not evaluated in the Low Desert zone. The monthly table above shows how the same rating translates into different gallon amounts as reference evapotranspiration changes.
Should I deadhead fern leaf yarrow?
Yes, deadheading promotes more flowers through summer. Cut finished stems down to the leaves. Leave a few heads if you want to dry them.
Why is my yarrow flopping over?
Too much water or fertilizer makes the stems weak. Wind also knocks tall stems down. Grow it lean and in a sheltered spot.
Can I dry fern leaf yarrow flowers?
Yes, the flower heads dry nicely and last a long time. Cut them when fully open. Hang them upside down in a dry, shady place.
Does fern leaf yarrow spread?
It spreads by rhizomes and seed. Divide clumps as needed to prevent crowding. Deadhead to limit seedlings.
What diseases affect fern leaf yarrow?
Stem rot, powdery mildew and rust can occur, and overwatering leads to root rot. Water at the base and let soil dry between soaks. Give it good air flow.
More plant watering guides
Sources
- WUCOLS IV plant water use classification for Achillea filipendulina, the University of California survey California agencies use for landscape plan reviewRead August 23, 2026 on wucols.ucdavis.edu
- Model Water Efficient Landscape Ordinance, adopted text and appendices, effective 2025-01-02 · monthly reference evapotranspiration per city, Appendix CRead August 23, 2026 on water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/Water-Use-And-Efficiency/MWELO-Rulemaking/Final-MWELO-Text-and-Appendices_20250103.pdf
- UC Statewide IPM Program, irrigation scheduling using evapotranspirationRead September 30, 2026 on ipm.ucanr.edu/PMG/GARDEN/ENVIRON/evap.html
- Shaw and Pittenger, Landscape Irrigation System Evaluation and Management, UC Cooperative Extension, 2009Read September 30, 2026 on ucanr.edu/sites/default/files/2013-02/160836.pdf
- Pittenger, Water Management in Gardens and Landscapes, UC Riverside, 2017Read September 30, 2026 on ucanr.edu/sites/default/files/2017-03/258022.pdf