WateringTimesWatering plan, $19
Quercus lobata, WUCOLS IV

How often to water valley oak in California

In July in the Central Valley, established valley oak in loam needs a deep watering about every 20 days: about 55 gallons each time under a 10 foot canopy, about 19 gallons a week. Valley oak is a deciduous California native and the fastest growing of the state's oaks, with deeply lobed leaves and a broad crown. It grows wild in the Central Valley, Sierra foothill valleys and the Coast Ranges, where its roots can reach year-round groundwater. A young tree shoots up quickly with water. An old tree suffers when soil stays wet around its trunk.

TreeCalifornia nativeUC Arboretum All-StarRated for 4 of 6 zones

How often to water valley oak, 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 valley oak 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

  • Dry soil 6 inches down at the edge of a young valley oak's root ball means it is time for a deep soak
  • Little or no new shoot growth on a young tree in summer, with dry soil below, points to a thirsty root zone
  • Wilting while the soil is moist can mean crown rot, so check the bark at the soil line for dark patches
  • White fungal fans between the bark and wood near the base point to oak root fungus, which wet soil near the crown favors
  • Leaf drop in fall and bare winter branches are normal for this deciduous oak and do not mean thirst

How to water it

  • Water a young valley oak over its root ball and a widening ring beyond it, since its fast early growth spreads the roots
  • Keep summer water at least 10 feet from the trunk of an established tree, or put it in the outer two-thirds of the root zone
  • Aim sprinklers and drip so water never hits the trunk or pools at the root crown
  • Leave the root crown uncovered, with no soil or mulch piled against the trunk
  • Do not add a new lawn under an old valley oak, though a young tree planted into a lawn can thrive

Through the seasons

Give a young valley oak deep soakings in summer while it shoots up as a slender whip before the crown fills out. In the wild, established trees live on groundwater and winter rain. During long droughts, summer water kept well away from the trunk has helped old trees survive. Leaves drop in fall and the tree rests bare through winter. Winter rain covers the cool months on the north-central coast and in the Central Valley, where WUCOLS rates it low water. It rates moderate water on the south coast and in South Inland. WUCOLS marks it as not suited to the high desert or the low desert.

In pots

Valley oak grows fast and reaches for groundwater, so keep it in a container only as a seedling waiting to be planted. Use a tall pot and check the mix 2 to 3 inches down every few days in summer. In Central Valley heat, check it daily. Water until it drains from the holes, then empty the saucer. Keep the root crown level with the mix, never buried. Plant it out early, because the young tree soon fills a pot with roots. Once the leaves drop in fall, the bare tree needs only light watering.

1 Your climate zone six WUCOLS zones, each from its own reference city
1.07gal per sq ft in JulyLow water use in the Central Valley zone
A year
6.84 gal per sq ft
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses
0.631.31.92.50.16JAN0.26FEB0.43MAR0.61APR0.83MAY0.99JUN1.07JUL0.95AUG0.72SEP0.47OCT0.22NOV0.14DEC0.631.31.92.50.16JFM0.61AMJ1.07JAS0.47OND
Gallons per square foot per month, Central Valley. Peak 1.07 in Jul, 6.84 a year.

Monthly water need by climate zone

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

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.150.160.780.78––
Feb0.210.260.810.87––
Mar0.350.431.151.3––
Apr0.470.611.41.61––
May0.580.831.611.95––
Jun0.640.991.742.29––
Jul0.641.071.982.51––
Aug0.60.951.862.33––
Sep0.50.721.491.86––
Oct0.350.471.151.33––
Nov0.190.220.840.9––
Dec0.120.140.650.68––
Year4.86.8415.518.41––

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

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 valley oak, 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 valley oak in summer?

In July, established valley oak in loam needs a deep watering about every 20 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 valley oak need per day?

In July in the Central Valley, established valley oak needs about 2.7 gallons a day under a 10 foot canopy and about 11 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 valley oak change across California?

Yes. WUCOLS rates valley oak separately for each of the six California climate zones: low water in the North-Central Coastal zone, low water in the Central Valley zone, moderate water in the South Coastal zone, moderate water 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.

Can I water under an old valley oak?

Keep regular water at least 10 feet from the trunk and away from the root crown. Soil kept wet at the base favors oak root fungus and crown rot. In a long drought, a deep soak in the outer part of the root zone can help the tree.

Can valley oak grow in a lawn?

A young valley oak planted into a lawn can do well, because it grows up with that watering. Adding a new lawn under an old tree is different, and it can kill the tree. Either way, keep sprinkler spray off the trunk.

How fast does valley oak grow?

Fast for an oak. With water, a young tree can reach about 20 feet in five years and add as much again in the next five. Height growth then slows as the crown fills out.

Why are old valley oaks dying in some valleys?

Valley oaks depend on access to groundwater. Native plant growers have seen whole stands die where the water table dropped far below the surface. Old trees can also decline when a lawn or frequent watering is added around the trunk.

Is valley oak good for wildlife?

Yes. Birds eat the acorns and nest in the limbs. Deer also browse the leaves when other food runs short.

More plant watering guides

AgapanthusGeraniumsOlive TreesFig TreesCrape MyrtleWisteriaLantanaSalvia

Sources