WateringTimesWatering plan, $19
Populus fremontii, WUCOLS IV

How often to water western cottonwood in California

In July in the Central Valley, established western cottonwood 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. Western cottonwood, also called Fremont cottonwood, is a native deciduous tree of rivers, creeks and washes across California. With regular water it grows astonishingly fast and becomes a broad shade tree loved by birds and butterflies. Female trees release cotton. It tolerates sand, clay and seasonal flooding, but shallow watering makes its roots shallow too.

TreeCalifornia nativeRated for 6 of 6 zones

How often to water western cottonwood, 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 western cottonwood 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

  • Ground dry 2 feet below the surface beyond the canopy in summer means western cottonwood needs a deep soak
  • Leaves yellowing and dropping in midsummer can indicate a dry root zone
  • Leaf edges browning in hot, dry wind can follow drought stress
  • Roots heaving up a nearby lawn point to frequent shallow watering

How to water it

  • Give long, slow soaks that wet the soil 2 feet or more beneath and beyond the crown
  • Space waterings so the upper soil dries between them, which pushes roots deeper
  • Plant far from septic systems, pipes and power lines
  • Keep nearby lawn watering infrequent so roots do not stay at the surface
  • Choose a male tree if cotton would be a nuisance

Through the seasons

Water a young western cottonwood deeply and often through its first summers, and it will race upward. Established trees still need deep water in dry months, since they grow naturally along streams. It is deciduous and rests bare in winter. Deep, widely spaced soaks give it deep roots. WUCOLS rates western cottonwood moderate water on the north-central coast, in the Central Valley, on the south coast and in South Inland. In the high desert and the low desert it carries a high water rating.

In pots

Western cottonwood grows far too fast for a container, sometimes many feet in a single year. A cutting or young tree can sit in a deep pot for a few months before planting. Water when the top couple of inches dry, letting it drain fully, and check daily in summer heat. Empty the saucer. Plant it out within the season, before roots circle the pot. Choose a sunny site with room overhead.

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
1.22.43.64.90.4JAN0.65FEB1.09MAR1.52APR2.08MAY2.48JUN2.67JUL2.39AUG1.8SEP1.18OCT0.56NOV0.34DEC1.22.43.64.90.4JFM1.52AMJ2.67JAS1.18OND
Gallons per square foot per month, Central Valley. Peak 2.67 in Jul, 17.11 a year.

Monthly water need by climate zone

Western Cottonwood: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.370.40.780.781.191.24
Feb0.530.650.810.871.491.49
Mar0.871.091.151.32.332.43
Apr1.181.521.41.613.033.12
May1.462.081.611.953.823.92
Jun1.612.481.742.294.564.46
Jul1.612.671.982.514.864.56
Aug1.492.391.862.334.464.17
Sep1.241.81.491.863.423.32
Oct0.871.181.151.332.332.38
Nov0.470.560.840.91.491.54
Dec0.310.340.650.681.041.09
Year1217.1115.518.4134.0333.73

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 western cottonwood. 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 western cottonwood 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 western cottonwood, 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 western cottonwood in summer?

In July, established western cottonwood in loam needs a deep watering about every 8 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 western cottonwood need per day?

In July in the Central Valley, established western cottonwood 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 western cottonwood change across California?

Yes. WUCOLS rates western cottonwood 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, moderate water in the South Inland zone, high water in the High and Intermediate Desert zone, high water in the Low Desert zone. The monthly table above shows how the same rating translates into different gallon amounts as reference evapotranspiration changes.

How fast does western cottonwood grow?

With regular water it is extremely fast, sometimes about 30 feet in a year on a good site. Plan for a big shade tree. Keep it away from power lines.

Why are cottonwood roots lifting my lawn?

Shallow, frequent lawn watering keeps its roots near the surface. Stretch lawn watering out and water the tree deeply instead. Roots then go deeper.

How do I avoid cotton from my tree?

Only female trees produce cotton. Plant a male tree. Some native nurseries grow only male trees for this reason.

Is western cottonwood native?

Yes, it is native along rivers and creeks across much of California. It supports many birds and butterflies. It suits large, wet sites.

Can western cottonwood grow near a septic system?

No, keep it well away from septic systems and pipes. Its roots seek out water aggressively. Plan its location carefully.

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Sources