WateringTimesWatering plan, $19
Quercus agrifolia, WUCOLS IV

How often to water oak trees in California

In July in the Central Valley, established oak trees in loam need a deep soak only about once a month or less: about 55 gallons each time under a 10 foot canopy. Coast live oak is a California evergreen with a wide root system extending beyond its canopy. Young trees need help while those roots establish. Around mature trees, careful placement matters: persistent warm, wet soil near the crown can favor root disease.

TreeCalifornia nativeRated for 5 of 6 zones

How often to water oak trees, 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 oak trees 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 to 6 inches down at the edge of a young oak root ball signals that it needs water
  • Dull, folded leaves, wilted shoot tips and early acorn drop on a young oak warrant a check for dry soil
  • Older interior leaves are replaced mainly in spring, so some shedding does not establish thirst
  • Mushrooms or dark, oozing bark near a wet trunk base warrant inspection for root disease
  • Branch dieback can accompany irrigation trouble, drought, borers or disease rather than identifying one watering fault

How to water it

  • Water a young coast live oak over its root ball and nearby soil, widening coverage as roots spread
  • Use drip or a slow hose to moisten the young oak's full root ball without pooling water against its trunk
  • Keep irrigation at least 10 feet from an established oak trunk, and keep a young trunk clear of direct spray
  • Place any mature-tree irrigation toward the outer canopy and beyond, keeping the ground near the root crown dry
  • Leave fallen oak leaves as mulch and keep lawn and thirsty plantings away from the crown and canopy area

Through the seasons

Give new coast live oaks deep soakings through their first summers, tapering help as roots spread. Established coastal and Central Valley trees often rely on winter and spring rain; avoid routine summer wetting near the crown. South Inland and low-desert trees need soil checks for summer irrigation placed away from the trunk. This evergreen replaces older leaves mainly in spring. Check low-desert soil during dry winter spells. WUCOLS rates it very low water on the north-central coast, in the Central Valley and on the south coast. It rates low water in South Inland and moderate water in the low desert. WUCOLS marks it as not suited to the high desert.

In pots

A coast live oak seedling develops a taproot early, so use a deep container and plan to plant it out while young. Check the mix two to three inches down often in California summer heat. Water when it dries, allowing excess to leave the drainage holes, then empty the saucer. Give the roots time to drain between soakings. In winter, rain may supply an exposed pot, but check beneath the surface during dry spells before deciding whether it needs water.

1 Your climate zone six WUCOLS zones, each from its own reference city
0.27gal per sq ft in JulyVery low water use in the Central Valley zone
A year
1.71 gal per sq ft
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses
0.711.42.12.90.04JAN0.07FEB0.11MAR0.15APR0.21MAY0.25JUN0.27JUL0.24AUG0.18SEP0.12OCT0.06NOV0.03DEC0.711.42.12.90.04JFM0.15AMJ0.27JAS0.12OND
Gallons per square foot per month, Central Valley. Peak 0.27 in Jul, 1.71 a year.

Monthly water need by climate zone

Oak Trees: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.040.040.080.31–0.78
Feb0.050.070.080.35–0.93
Mar0.090.110.110.52–1.52
Apr0.120.150.140.64–1.95
May0.150.210.160.78–2.45
Jun0.160.250.170.92–2.79
Jul0.160.270.21–2.85
Aug0.150.240.190.93–2.6
Sep0.120.180.150.74–2.08
Oct0.090.120.110.53–1.49
Nov0.050.060.080.36–0.96
Dec0.030.030.070.27–0.68
Year1.21.711.557.37–21.08

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 very low water in the Central Valley, like oak trees. Plants that drink alike can share one valve and one schedule.

Salt CedarTamarix aphyllavery low water, Central Valley0.27 gal/sq ft in JulyPearl AcaciaAcacia podalyriifoliavery low water, Central Valley0.27 gal/sq ft in JulyMexican Palo VerdeParkinsonia aculeatavery low water, Central Valley0.27 gal/sq ft in JulyFoothill PinePinus sabinianavery low water, Central Valley0.27 gal/sq ft in JulyInterior Live OakQuercus wislizenivery low water, Central Valley0.27 gal/sq ft in JulyBlue OakQuercus douglasiivery low water, Central Valley0.27 gal/sq ft in JulyNuttall's Scrub OakQuercus dumosavery low water, Central Valley0.27 gal/sq ft in JulyCalifornia BuckeyeAesculus californicavery low water, Central Valley0.27 gal/sq ft in JulyTree of HeavenAilanthus altissimavery low water, Central Valley0.27 gal/sq ft in JulyOleanderNerium oleander ssp. & cvs.very low water, Central Valley0.27 gal/sq ft in JulyAgaveAgave americana (and thick-leaved relatives)very low water, Central Valley0.27 gal/sq ft in JulyCactusOpuntia spp. & cvs. (CA natives and non-natives)very low water, Central Valley0.27 gal/sq ft in JulySpanish BroomSpartium junceumvery low water, Central Valley0.27 gal/sq ft in JulyBig SagebrushArtemisia tridentatavery low water, Central Valley0.27 gal/sq ft in JulyCalifornia PoppyEschscholzia californicavery low water, Central Valley0.27 gal/sq ft in JulyCalifornia Scrub OakQuercus berberidifoliavery low water, Central Valley0.27 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 oak trees, 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 oak trees in summer?

In July, established oak trees in loam need a deep watering about once a month or less in the Central Valley, about once a month or less on the south coast and about every 22 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 do oak trees need per day?

In July in the Central Valley, established oak trees need about 0.7 gallons a day under a 10 foot canopy and about 2.7 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 oak trees change across California?

Yes. WUCOLS rates oak trees separately for each of the six California climate zones: very low water in the North-Central Coastal zone, very low water in the Central Valley zone, very low water in the South Coastal zone, low water in the South Inland zone, not suited to this region in the High and Intermediate Desert zone, moderate 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 do I water a newly planted coast live oak?

Check at the root ball edge before soaking. Wet its full depth without leaving the trunk in standing water. Expand the wet area as the tree grows rather than confining irrigation to the planting hole.

Should I change irrigation around a mature oak?

If the tree has received irrigation for years, reduce it gradually rather than stopping abruptly. Move remaining water toward the canopy edge and beyond. Warm, saturated ground near the trunk deserves a drainage and crown check.

Can I grow a lawn or garden under an oak?

Frequent lawn watering can keep the crown area wet through summer. Keep turf and thirsty beds outside the canopy. Any planting beneath an established coastal oak should share its dry-summer care and stay away from the trunk.

How do I water an oak grown from an acorn?

Keep a potted acorn seedling's mix lightly moist while its taproot develops, allowing only slight surface drying. Plant out before roots circle the container.

Does this guide also rate valley oak?

No. These classes belong to coast live oak. Valley oak is a different species, so do not transfer the regional figures to it.

More plant watering guides

Fox Tail AgaveSaltbushParry's AgaveOleanderAgaveCactusSpanish BroomSalt Cedar

Sources