WateringTimesWatering plan, $19
Fraxinus latifolia, WUCOLS IV

How often to water Oregon ash in California

In July in the Central Valley, established Oregon 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. Oregon ash is a deciduous native tree of stream banks, bottomlands and wet meadows along the Pacific coast. It grows fast while young, then slows, and its leaves turn yellow in fall. It tolerates wet clay and seasonal flooding. It is not a dry garden tree, though, and long dry spells stunt its growth and strip its leaves.

TreeCalifornia nativeRated for 3 of 6 zones

How often to water Oregon 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 Oregon 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 4 inches down at the edge of a young Oregon ash's root ball means the tree is ready for a deep soak
  • Leaves dropping in midsummer, well before the yellow fall color, point to a root zone that has dried out
  • Short, stunted shoots on a young tree can follow repeated dry spells during the growing season
  • Leaf spots or a powdery white coating on the leaflets come from fungi, so check the soil before changing the water
  • Leaves that sicken while the ground stays damp call for a look at disease or injury, since this tree tolerates wet clay and seasonal flooding

How to water it

  • Water a young Oregon ash over its root ball and a ring of soil beyond it, widening the ring as the crown spreads
  • Run water slowly so it sinks well below the surface, and let only the top few inches dry before the next soak
  • Set drip emitters or a soaker ring under the outer canopy of an older tree instead of spraying the trunk
  • Spread wood chip mulch across the root zone to hold moisture, keeping it a few inches off the bark
  • Plant it in a low, moist spot such as a swale or the edge of a rain garden, where heavy clay suits it well

Through the seasons

Give a new Oregon ash deep soakings through its first few summers while its roots spread. An established tree still prefers moist soil, and dry conditions stunt its growth and invite disease. It comes from places with cool, humid summers, so hot inland summers are when soil checks matter most. Small flowers open in spring, and the leaves turn yellow and drop in fall. Winter rain covers the cool months while the tree is bare. WUCOLS rates Oregon ash moderate water on the north-central coast, in the Central Valley and on the south coast. WUCOLS marks it as not suited to South Inland, the high desert or the low desert.

In pots

Oregon ash grows into a large tree, so a container suits it only as a young nursery plant waiting to go in the ground. It likes steady moisture, so do not let the mix dry out completely. Check a nursery can 2 inches down every few days in summer, and daily during a Central Valley heat wave. Water until it drains from the holes, then empty the saucer. Shade a dark can that sits on hot paving. Once the leaves drop in fall, the bare tree uses far less, so check the mix during dry winter weeks and let rain do most of the work.

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
0.671.32.02.70.4JAN0.65FEB1.09MAR1.52APR2.08MAY2.48JUN2.67JUL2.39AUG1.8SEP1.18OCT0.56NOV0.34DEC0.671.32.02.70.4JFM1.52AMJ2.67JAS1.18OND
Gallons per square foot per month, Central Valley. Peak 2.67 in Jul, 17.11 a year.

Monthly water need by climate zone

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

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.370.40.78–––
Feb0.530.650.81–––
Mar0.871.091.15–––
Apr1.181.521.4–––
May1.462.081.61–––
Jun1.612.481.74–––
Jul1.612.671.98–––
Aug1.492.391.86–––
Sep1.241.81.49–––
Oct0.871.181.15–––
Nov0.470.560.84–––
Dec0.310.340.65–––
Year1217.1115.5–––

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 Oregon 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 Oregon 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 Oregon 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 often should I water Oregon ash in summer?

In July, established Oregon ash in loam needs a deep watering about every 8 days in the Central Valley and about every 11 days on the south coast. 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 Oregon ash need per day?

In July in the Central Valley, established Oregon 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 Oregon ash change across California?

Yes. WUCOLS rates Oregon ash separately for each of the six California climate zones: moderate water in the North-Central Coastal zone, moderate water in the Central Valley zone, moderate water in the South Coastal zone, not suited to this region in the South Inland zone, not suited to this region 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.

Is Oregon ash a California native?

Yes. It grows wild from southwestern Canada to California, along streams, in bottomlands and in wet meadows. In California it usually grows in sheltered spots and stays smaller than the old giants of Oregon.

How big does Oregon ash get?

Wild trees can reach 65 to 80 feet and live up to 250 years. In most California gardens, expect something nearer 30 to 40 feet after fifty years. It grows fast while young and slows with age.

Why does my Oregon ash have no seeds?

Male and female flowers grow on separate trees. Only female trees make the winged seeds, which hang in clusters in fall. A female tree also needs a male tree nearby to set seed.

Can Oregon ash grow in wet clay?

Yes. In the wild it grows on deep, poorly drained clays and tolerates occasional flooding. That makes it a good fit for a swale, a rain garden or a low, damp corner of the yard.

Why is my Oregon ash losing leaves in summer?

Dry soil is a common cause, since drought makes this tree drop leaves and stunts its growth. Check 4 inches down under the outer canopy and soak deeply if it is dry. A stressed tree is also more open to disease.

Does Oregon ash help wildlife?

Yes. Songbirds, squirrels and waterfowl eat the seeds, and the tree feeds some butterfly larvae. Deer and elk browse the leaves and young sprouts, so protect a young tree where deer roam.

More plant watering guides

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Sources