WateringTimesWatering plan, $19
Sorbus aucuparia, WUCOLS IV

How often to water European mountain ash in California

In July in the Central Valley, established European mountain ash in loam needs a deep watering about every 8 days: about 55 gallons each time under a 10 foot canopy, about 47 gallons a week. European mountain ash, also called rowan, is a small deciduous tree grown for white spring flowers and orange-red fall berries. It prefers steady soil moisture and struggles wherever heat or drought stress its roots. Stressed trees also become more open to borers and canker.

TreeRated for 2 of 6 zones

How often to water European mountain ash, month by month

Your city
Canopy width
10 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 European mountain ash 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 under the branches, 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 canopy width

A tree with its canopy width marked across the widest branches and the circle under it shaded blue

Measure across the branches, from the tips of the outer leaves on one side to the tips on the other. A tape works, or pace it out.

Water the whole circle under the branches, shown in blue. The gallons here cover that circle.

A wider canopy means more gallons each watering, not more waterings. While the tree is young, measure again each spring.

How to tell it needs water

  • Soil dry several inches down at the drip line signals a mountain ash needs a deep soak
  • Leaf margins scorching brown during a hot spell can follow dry soil at the roots
  • Early, heavy leaf drop in summer warrants a check for scab as well as a soil check
  • Sunken, discolored bark patches on a stressed tree warrant a check for canker or borers rather than assuming thirst
  • Yellowing leaves over soggy, compacted soil can indicate roots sitting in standing water

How to water it

  • Water a young mountain ash over its full root ball, widening coverage as the roots spread
  • Soak the root zone out to the drip line with drip or a slow hose rather than brief overhead sprinkling
  • Keep the soil around the base loose and free of compaction, since this tree dislikes packed ground
  • Mulch out to the drip line while keeping mulch clear of the trunk itself
  • Avoid wetting blossoms and new shoots, since damp growth can favor fire blight

Through the seasons

A newly planted mountain ash needs consistent soil moisture through its first summers while its root system establishes. This deciduous tree flowers in spring, fruits in late summer, and drops its leaves in fall before winter dormancy. Irrigation matters most from spring through early fall during active growth and fruiting. Stressed, dry roots leave the tree more open to borers and canker, so avoid letting the soil dry out fully in the growing season. Winter rain covers the cool months in the Central Valley, where WUCOLS rates it moderate water, matching the high desert rating. WUCOLS marks it as not suited to the north-central coast, the south coast, South Inland or the low desert.

In pots

A young European mountain ash can grow in a large container for its first seasons before an open-ground planting. Check the mix several inches down often during California summer heat, since containers dry faster than garden beds. Water when it dries, let excess drain fully through the holes, then empty the saucer so roots avoid standing water. This deciduous tree needs less water once its leaves drop for winter.

1 Your climate zone six WUCOLS zones, each from its own reference city
2.67gal per sq ft in JulyModerate water use in the Central Valley zone
A year
17.11 gal per sq ft
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses
0.761.52.33.00.4JAN0.65FEB1.09MAR1.52APR2.08MAY2.48JUN2.67JUL2.39AUG1.8SEP1.18OCT0.56NOV0.34DEC0.761.52.33.00.4JFM1.52AMJ2.67JAS1.18OND
Gallons per square foot per month, Central Valley. Peak 2.67 in Jul, 17.11 a year.

Monthly water need by climate zone

European Mountain Ash: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan–0.4––0.74–
Feb–0.65––0.93–
Mar–1.09––1.46–
Apr–1.52––1.89–
May–2.08––2.39–
Jun–2.48––2.85–
Jul–2.67––3.04–
Aug–2.39––2.79–
Sep–1.8––2.14–
Oct–1.18––1.46–
Nov–0.56––0.93–
Dec–0.34––0.65–
Year–17.11––21.27–

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 moderate water in the Central Valley, like European mountain ash. Plants that drink alike can share one valve and one schedule.

Citrus TreesCitrus spp.moderate water, Central Valley2.67 gal/sq ft in JulyJapanese MapleAcer palmatummoderate water, Central Valley2.67 gal/sq ft in JulyAvocado TreesPersea americanamoderate water, Central Valley2.67 gal/sq ft in JulyMagnolia TreesMagnolia grandiflora ssp. & cvs.moderate water, Central Valley2.67 gal/sq ft in JulyPalm TreesSyagrus romanzoffiana (Arecastrum romanzoffianum)moderate water, Central Valley2.67 gal/sq ft in JulyApple TreesMalus spp. (edible) e.g, 'Anna' (low chill variety for low desert)moderate water, Central Valley2.67 gal/sq ft in JulyPeach TreesPrunus spp. ediblemoderate water, Central Valley2.67 gal/sq ft in JulyPersimmon TreesDiospyros kakimoderate water, Central Valley2.67 gal/sq ft in JulyAmur MapleAcer ginnalamoderate water, Central Valley2.67 gal/sq ft in JulyFernleaf MapleAcer japonicummoderate water, Central Valley2.67 gal/sq ft in JulyBox ElderAcer negundomoderate water, Central Valley2.67 gal/sq ft in JulyNorway MapleAcer platanoidesmoderate water, Central Valley2.67 gal/sq ft in JulyRed MapleAcer rubrummoderate water, Central Valley2.67 gal/sq ft in JulyChinese MapleAcer truncatummoderate water, Central Valley2.67 gal/sq ft in JulyRed BuckeyeAesculus paviamoderate water, Central Valley2.67 gal/sq ft in JulyRed HorsechestnutAesculus x carneamoderate water, Central Valley2.67 gal/sq ft in July

Similar plants that need less water 16

Rated lower than European mountain ash in the Central Valley. Worth a look for a new bed or a lawn replacement.

Olive TreesOlea europaea ssp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyFig TreesFicus carica ssp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyCrape MyrtleLagerstroemia spp., hybrids & cvs.low water, Central Valley1.07 gal/sq ft in JulyAloeAloe spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyPomegranate TreesPunica granatumlow water, Central Valley1.07 gal/sq ft in JulyEucalyptusEucalyptus polyanthemoslow water, Central Valley1.07 gal/sq ft in JulyPine TreesPinus canariensislow water, Central Valley1.07 gal/sq ft in JulyJunipersJuniperus spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyTexas Red OakQuercus buckleyilow water, Central Valley1.07 gal/sq ft in JulyPortuguese OakQuercus faginealow water, Central Valley1.07 gal/sq ft in JulySoapbark TreeQuillaja saponarialow water, Central Valley1.07 gal/sq ft in JulyNecklace TreeSophora affinislow water, Central Valley1.07 gal/sq ft in JulyBailey AcaciaAcacia baileyanalow water, Central Valley1.07 gal/sq ft in JulySilver WattleAcacia dealbatalow water, Central Valley1.07 gal/sq ft in JulyGreen WattleAcacia decurrenslow water, Central Valley1.07 gal/sq ft in JulySydney Golden WattleAcacia longifolialow 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 European mountain ash, 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 much water does European mountain ash need per day?

In July in the Central Valley, established European mountain ash needs about 6.8 gallons a day under a 10 foot canopy and about 27 gallons a day under a 20 foot canopy. Give it in deep waterings spread days apart rather than a little every day, so the whole root zone gets wet.

Does watering for European mountain ash change across California?

Yes. WUCOLS rates European mountain ash separately for each of the six California climate zones: not suited to this region in the North-Central Coastal zone, moderate water in the Central Valley zone, not suited to this region in the South Coastal zone, not suited to this region in the South Inland zone, moderate water in the High and Intermediate Desert zone, not suited to this region in the Low Desert zone. The monthly table above shows how the same rating translates into different gallon amounts as reference evapotranspiration changes.

Why is my European mountain ash dropping leaves early?

Scab, a leaf disease, can cause heavy leaf loss on this tree, so look for dark spots on the leaves. Check soil moisture too at the first sign of wilting or scorched leaf edges. This tree does best where summers stay milder than the hottest California inland spots.

How do I water a newly planted mountain ash?

Keep the original root ball moist separately from the surrounding soil while new roots form. Widen the soaked area gradually over the first couple of growing seasons. Avoid letting the root ball dry out completely during establishment.

Is European mountain ash prone to fire blight?

Fire blight can be a serious problem for this tree, especially on wet blossoms or fresh shoots. Avoid wetting flowers and new growth directly. Prune out infected wood promptly and clean tools between cuts.

Can this tree handle compacted or heavy soil?

It dislikes compacted ground, which limits both drainage and root growth. Loosen the soil before planting and keep the area around the trunk from becoming packed down. Good drainage matters as much as adequate moisture here.

Why does my mountain ash have sunken bark patches?

Sunken or discolored bark on a stressed tree can point to canker or borer activity rather than a watering problem alone. Prolonged dry soil often precedes these issues. Have a stressed tree checked rather than only increasing water.

Does European mountain ash suit a low desert or coastal yard?

WUCOLS rates this tree only for the Central Valley and the high desert. Every other California region covered here is not listed as suited for it. Choose a species matched to your own zone before planting.

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Sources