WateringTimesWatering plan, $19
Achillea tomentosa, WUCOLS IV

How often to water woolly yarrow in California

In July in the Central Valley, established woolly yarrow in loam needs a deep watering about every 20 days: about 2.2 gallons each time for a plant 2 feet across, about 0.8 gallons a week. Woolly yarrow is a low, spreading perennial from southern Europe and western Asia, with gray-green, woolly, fern-like leaves that smell spicy when crushed. Flat clusters of small yellow flowers rise above the mat from late spring into summer. It tolerates dry spells and poor soil, but heavy clay and moist, rich ground work against it.

Ground coverPerennialRated for 4 of 6 zones

How often to water woolly yarrow, month by month

Your city
Plant width
2 ft
Your soil

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.

Every month, on your water days. The personal plan prints this for woolly yarrow and the rest of your yard, on the days your water supplier allows.Get the plan for $19

How this is worked out: established roots fill the top 1.5 feet 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.

Which soil do you have?

Dig down a few inches, take a handful of moist soil and squeeze it.

  • Sandy: gritty, falls apart when you open your hand, will not form a ball.
  • Loam: forms a soft ball that crumbles when you poke it.
  • Clay: forms a firm, sticky ball and squeezes out into a ribbon between thumb and finger.

Still not sure? Pick loam. Most garden beds sit between sand and clay.

How to measure plant width

A shrub with its width marked from one side to the other and the circle under it shaded blue

Measure across the plant, from the tips of the leaves on one side to the tips on the other.

Water the whole area the plant covers, shown in blue. The gallons here cover that area.

A wider plant means more gallons each watering, not more waterings. While it is young, measure again each spring.

How to tell it needs water

  • Soil that has dried an inch or two below the woolly mat in summer heat is the cue to water
  • Stems that collapse at the base in soil that stays wet warrant a check for stem rot, an occasional problem for woolly yarrow
  • A white powdery coating or rusty spots on the leaves point to powdery mildew or rust, not to a lack of water
  • Flower stems flattened after heavy rain and wind show storm damage rather than thirst

How to water it

  • Water at the edge of the mat with drip or a soaker line so the woolly leaves stay dry
  • Soak the root zone, then let the top inch or two of soil dry before watering again
  • Plant in lean, sandy or rocky soil that drains quickly, and skip rich amendments and heavy clay
  • Use slopes, rock garden pockets or the gaps between stepping stones, where water runs off instead of pooling
  • Extend drip coverage as the mat spreads, and divide clumps once they become crowded

Through the seasons

Keep a new planting lightly moist until roots reach into the surrounding soil, then water less often and more deeply. Woolly yarrow flowers from late spring into summer, and watering matters most through that stretch. Winter rain covers the cool months on the north-central coast and in the Central Valley, where WUCOLS rates it low water. It rates moderate water on the south coast and in South Inland, where summer soil checks matter more. WUCOLS has not evaluated it for the high desert or the low desert, so gardeners there should rely on soil checks.

In pots

Woolly yarrow grows in containers as well as in the ground. Use a lean, gritty mix rather than a rich one that holds moisture, in a pot with drainage holes. In summer heat, feel the mix under the edge of the mat every few days and water once the top inch or two is dry. Water at the soil line until it drains, then empty the saucer so the mat does not sit over soggy mix. Divide the plant when it crowds the pot. In winter, check after rain that the mix is not staying wet, and let it dry between waterings.

1 Your climate zone six WUCOLS zones, each from its own reference city
1.07gal per sq ft in JulyLow water use in the Central Valley zone
A year
6.84 gal per sq ft
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses
0.631.31.92.50.16JAN0.26FEB0.43MAR0.61APR0.83MAY0.99JUN1.07JUL0.95AUG0.72SEP0.47OCT0.22NOV0.14DEC0.631.31.92.50.16JFM0.61AMJ1.07JAS0.47OND
Gallons per square foot per month, Central Valley. Peak 1.07 in Jul, 6.84 a year.

Monthly water need by climate zone

Woolly Yarrow: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.150.160.780.78––
Feb0.210.260.810.87––
Mar0.350.431.151.3––
Apr0.470.611.41.61––
May0.580.831.611.95––
Jun0.640.991.742.29––
Jul0.641.071.982.51––
Aug0.60.951.862.33––
Sep0.50.721.491.86––
Oct0.350.471.151.33––
Nov0.190.220.840.9––
Dec0.120.140.650.68––
Year4.86.8415.518.41––

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 woolly yarrow. Plants that drink alike can share one valve and one schedule.

BougainvilleaBougainvillea & spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyAgapanthusAgapanthus orientalislow water, Central Valley1.07 gal/sq ft in JulyGeraniumsPelargonium x hortorum and cvs.low water, Central Valley1.07 gal/sq ft in JulyLantanaLantana camara ssp. & cvs.low water, Central Valley1.07 gal/sq ft in JulySalviaSalvia greggii ssp., cvs. & hybridslow water, Central Valley1.07 gal/sq ft in JulyIrisesIris germanicalow water, Central Valley1.07 gal/sq ft in JulySucculentsEcheveria spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyJunipersJuniperus spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyRussian SagePerovskia spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyYarrowAchillea millefolium (non-native hybrids)low water, Central Valley1.07 gal/sq ft in JulyMountain AlyssumAlyssum montanumlow water, Central Valley1.07 gal/sq ft in JulySagebrushArtemisia spp. (shrubby)low water, Central Valley1.07 gal/sq ft in JulySilver SageSalvia argentealow water, Central Valley1.07 gal/sq ft in JulyPurple MulleinVerbascum phoeniceumlow water, Central Valley1.07 gal/sq ft in JulySilvery YarrowAchillea clavennaelow water, Central Valley1.07 gal/sq ft in JulyFern Leaf YarrowAchillea filipendulinalow water, Central Valley1.07 gal/sq ft in July
Minutes for your sprinklers

Turn this into minutes on your water days

Every city page has a calculator that takes woolly 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 woolly yarrow in summer?

In July, established woolly yarrow in loam needs a deep watering about every 20 days in the Central Valley, about every 11 days on the south coast and about every 9 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 woolly yarrow need per day?

In July in the Central Valley, established woolly 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 woolly yarrow change across California?

Yes. WUCOLS rates woolly 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, moderate water in the South Coastal zone, moderate 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.

Can you walk on woolly yarrow?

It withstands light foot traffic, which makes it useful between stepping stones and along path edges. It is not built for a play area or a busy lawn. Keep regular foot traffic on pavers and let the mat fill the gaps.

Should I deadhead woolly yarrow?

Yes. Removing spent flower heads can bring more bloom and keeps it from spreading outside the bed, since it can be weedy. Cutting the stems back to the basal leaves after flowering tidies the mat and can encourage a second bloom in fall.

What soil does woolly yarrow need?

Lean, well-drained soil suits it best, including sandy or rocky ground. It tolerates poor soil as long as water drains away. Avoid planting it in clay that stays wet or in rich, moist beds.

Is woolly yarrow deer resistant?

Yes. Deer and rabbits tend to leave it alone. Its flowers draw bees and butterflies, so it suits pollinator plantings.

Does woolly yarrow do well in hot inland gardens?

It does best where summers are cooler, and hot, humid weather weakens it. In a hot garden, keep the drainage sharp and check the soil before each soak rather than watering by habit.

More plant watering guides

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Sources