How often to water green ash in California
In July in the Central Valley, established green 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. Green ash is a fast, adaptable deciduous shade tree from the riverbanks and floodplains of central and eastern North America. It has compound leaves and gray-brown bark with diamond-patterned ridges. Most garden trees are seedless males, since females drop masses of winged seeds, and it tolerates occasional flooding but still needs deep summer soakings.
How often to water green ash, 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 1.5 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.
How to tell it needs water
- Soil dry 6 inches down under the canopy in summer signals that a green ash needs a deep soak
- Leaves browning at the edges or dropping early in late summer can follow a dry root zone
- Brown blotches on young leaves after a wet spring can point to anthracnose, not thirst
- Clouds of tiny white insects and sticky, sooty leaves point to whiteflies, a pest problem rather than a water one
- A thinning crown with soft bark at the base over constantly wet soil warrants a check for root rot
How to water it
- Water slowly under the canopy with drip or a soaker, keeping the trunk dry
- Soak to about 2 feet deep, and let the top several inches dry before the next watering
- Plant in full sun to light shade in moist, well-drained clay or loam
- Give the tree its own drip zone so lawn watering does not set its schedule
- Move irrigation outward as the crown spreads toward 35 to 50 feet
Through the seasons
Young green ash trees need deep soakings through their first two or three summers as roots move into native soil. Established trees handle short dry spells and occasional flooding, but they still want deep soakings through the dry season. Leaves emerge in spring and take on fall color before dropping. Rain usually waters the leafless tree on the north-central coast and in the Central Valley. WUCOLS rates green ash moderate water on the north-central coast and in the Central Valley. The other four zones, the south coast, South Inland, the high desert and the low desert, have not been evaluated.
In pots
Green ash grows into a large shade tree, so a container suits only a young nursery tree for a short time. Check the mix 2 to 3 inches below the surface every few days in summer, and water until it drains through. Empty the saucer each time. Plant it out before the roots circle the pot. After leaf fall, water the dormant tree only when the mix begins to dry.
- A year
- 17.11 gal per sq ft
- Reference
- Sacramento climate table
- Counts
- Plant need, before sprinkler losses
Monthly water need by climate zone
Green Ash: gallons per square foot per month, by WUCOLS climate zone
| Month | N. Coast | C. Valley | S. Coast | S. Inland | Hi Desert | Lo Desert |
|---|---|---|---|---|---|---|
| Jan | 0.37 | 0.4 | – | – | – | – |
| Feb | 0.53 | 0.65 | – | – | – | – |
| Mar | 0.87 | 1.09 | – | – | – | – |
| Apr | 1.18 | 1.52 | – | – | – | – |
| May | 1.46 | 2.08 | – | – | – | – |
| Jun | 1.61 | 2.48 | – | – | – | – |
| Jul | 1.61 | 2.67 | – | – | – | – |
| Aug | 1.49 | 2.39 | – | – | – | – |
| Sep | 1.24 | 1.8 | – | – | – | – |
| Oct | 0.87 | 1.18 | – | – | – | – |
| Nov | 0.47 | 0.56 | – | – | – | – |
| Dec | 0.31 | 0.34 | – | – | – | – |
| Year | 12 | 17.11 | – | – | – | – |
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 green ash. Plants that drink alike can share one valve and one schedule.
Citrus TreesCitrus spp.moderate water, Central Valley2.67 gal/sq ft in July
Japanese MapleAcer palmatummoderate water, Central Valley2.67 gal/sq ft in July
Avocado TreesPersea americanamoderate water, Central Valley2.67 gal/sq ft in July
Magnolia TreesMagnolia grandiflora ssp. & cvs.moderate water, Central Valley2.67 gal/sq ft in July
Palm TreesSyagrus romanzoffiana (Arecastrum romanzoffianum)moderate water, Central Valley2.67 gal/sq ft in July
Apple TreesMalus spp. (edible) e.g, 'Anna' (low chill variety for low desert)moderate water, Central Valley2.67 gal/sq ft in July
Peach TreesPrunus spp. ediblemoderate water, Central Valley2.67 gal/sq ft in July
Persimmon TreesDiospyros kakimoderate water, Central Valley2.67 gal/sq ft in July
Amur MapleAcer ginnalamoderate water, Central Valley2.67 gal/sq ft in July
Fernleaf MapleAcer japonicummoderate water, Central Valley2.67 gal/sq ft in July
Box ElderAcer negundomoderate water, Central Valley2.67 gal/sq ft in July
Norway MapleAcer platanoidesmoderate water, Central Valley2.67 gal/sq ft in July
Red MapleAcer rubrummoderate water, Central Valley2.67 gal/sq ft in July
Chinese MapleAcer truncatummoderate water, Central Valley2.67 gal/sq ft in July
Red BuckeyeAesculus paviamoderate water, Central Valley2.67 gal/sq ft in July
Red HorsechestnutAesculus x carneamoderate water, Central Valley2.67 gal/sq ft in JulySimilar plants that need less water 16
Rated lower than green 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 July
Fig TreesFicus carica ssp. & cvs.low water, Central Valley1.07 gal/sq ft in July
Crape MyrtleLagerstroemia spp., hybrids & cvs.low water, Central Valley1.07 gal/sq ft in July
AloeAloe spp. & cvs.low water, Central Valley1.07 gal/sq ft in July
Pomegranate TreesPunica granatumlow water, Central Valley1.07 gal/sq ft in July
EucalyptusEucalyptus polyanthemoslow water, Central Valley1.07 gal/sq ft in July
Pine TreesPinus canariensislow water, Central Valley1.07 gal/sq ft in July
JunipersJuniperus spp. & cvs.low water, Central Valley1.07 gal/sq ft in July
Texas Red OakQuercus buckleyilow water, Central Valley1.07 gal/sq ft in July
Portuguese OakQuercus faginealow water, Central Valley1.07 gal/sq ft in July
Soapbark TreeQuillaja saponarialow water, Central Valley1.07 gal/sq ft in July
Necklace TreeSophora affinislow water, Central Valley1.07 gal/sq ft in July
Bailey AcaciaAcacia baileyanalow water, Central Valley1.07 gal/sq ft in July
Silver WattleAcacia dealbatalow water, Central Valley1.07 gal/sq ft in July
Green WattleAcacia decurrenslow water, Central Valley1.07 gal/sq ft in July
Sydney Golden WattleAcacia longifolialow water, Central Valley1.07 gal/sq ft in JulyTurn this into minutes on your water days
Every city page has a calculator that takes green 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 green ash need per day?
In July in the Central Valley, established green 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 green ash change across California?
Yes. WUCOLS rates green 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, not evaluated in the South Coastal zone, not evaluated 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 still plant green ash?
New planting is no longer recommended in most regions because of the emerald ash borer, which has killed ash trees across much of the country. If you already have one, keep it vigorous with deep summer soakings and watch for borer damage.
What is a seedless green ash?
Female trees produce masses of winged seeds that litter the ground in fall. Male cultivars are seedless, which is why most landscape trees are males. Their pollen is listed as an allergy hazard, though.
Why is my green ash covered in sticky residue?
Whiteflies and scale insects feed on ash and leave sticky honeydew that grows black sooty mold. That is a pest problem, not a sign the tree needs water.
How big does green ash get?
It can grow 50 to 70 feet tall and 35 to 50 feet wide, pyramidal when young and rounder with age. Plan the watering zone around that mature spread.
Can green ash take wet soil?
Yes. It grows wild on floodplains and riverbanks and tolerates occasional flooding. It also handles alkaline soil and moderate salt.
More plant watering guides
Sources
- WUCOLS IV plant water use classification for Fraxinus pennsylvanica cvs., 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