WateringTimesWatering plan, $19
Eucalyptus sideroxylon, WUCOLS IV

How often to water red ironbark in California

In July in the Central Valley, established red ironbark 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. Red ironbark is a fast-growing evergreen eucalyptus from eastern Australia, with rough, deeply furrowed dark bark. Its habit ranges from upright to weeping, with blue-green leaves and fluffy pink flower clusters that honeybees visit. Once established it gets by on occasional deep soakings. Those soakings matter in long dry spells, since drought-stressed eucalyptus draw borers.

TreeRated for 6 of 6 zones

How often to water red ironbark, 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 red ironbark 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 6 inches down under the outer canopy of a young ironbark means it is time for a slow, deep soak
  • Discolored, wilting leaves and dying limbs after a long dry summer point to drought stress in the root zone
  • Holes in the bark with stains or oozing liquid on the trunk point to longhorned borers, which favor stressed trees
  • A thinning, yellowing crown over soil that stays wet around the trunk points to root rot rather than thirst
  • Leaves turning bronze in winter is normal for this tree and is not a sign that it needs water

How to water it

  • Water a young ironbark over its root ball and a ring beyond it, then move the wet band out as the canopy spreads
  • On an established tree, apply water under the outer edge of the canopy and keep it away from the trunk
  • Run drip emitters slowly until water reaches a foot or more below the surface, then let the soil dry well
  • Keep lawn sprinklers off its root zone, since frequent shallow watering favors root disease in eucalyptus
  • Plant in full sun in soil that drains at least moderately well, and never let water stand around the root crown

Through the seasons

Give a new ironbark slow, deep soakings through its first summers, until roots spread well past the planting hole. After that, water it in long dry spells. If the tree has been on regular irrigation, do not stop all at once, since sudden drought stress invites borers. The tree is evergreen and flowers between fall and spring. WUCOLS rates red ironbark low water on the north-central coast, in the Central Valley, on the south coast and in South Inland. Winter rain covers the cool months on the coast and in the Central Valley. It rates moderate water in the high desert and in the low desert, where dry winters call for soil checks.

In pots

Red ironbark grows far too large for a permanent container, so keep it in a nursery can only until planting time. Check the mix 2 inches down every few days in summer, and daily during inland or desert heat. Water until it runs from the drainage holes, then empty the saucer so the roots never sit in water. A dark can on hot paving heats fast, so shade the pot itself. In winter, cool weather slows drying, so test the mix with a finger before each 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
0.761.52.33.00.16JAN0.26FEB0.43MAR0.61APR0.83MAY0.99JUN1.07JUL0.95AUG0.72SEP0.47OCT0.22NOV0.14DEC0.761.52.33.00.16JFM0.61AMJ1.07JAS0.47OND
Gallons per square foot per month, Central Valley. Peak 1.07 in Jul, 6.84 a year.

Monthly water need by climate zone

Red Ironbark: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.150.160.310.310.740.78
Feb0.210.260.320.350.930.93
Mar0.350.430.460.521.461.52
Apr0.470.610.560.641.891.95
May0.580.830.640.782.392.45
Jun0.640.990.690.922.852.79
Jul0.641.070.7913.042.85
Aug0.60.950.740.932.792.6
Sep0.50.720.60.742.142.08
Oct0.350.470.460.531.461.49
Nov0.190.220.330.360.930.96
Dec0.120.140.260.270.650.68
Year4.86.846.27.3721.2721.08

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 low water in the Central Valley, like red ironbark. 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 red ironbark, 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 red ironbark in summer?

In July, established red ironbark in loam needs a deep watering about every 20 days in the Central Valley, about every 27 days 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 does red ironbark need per day?

In July in the Central Valley, established red ironbark 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 red ironbark change across California?

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

Does red ironbark attract bees?

Yes. Its fluffy pink flower clusters draw honeybees while the tree is in bloom. Plant it away from a pool or patio if bees near seating are a concern.

Why does my eucalyptus have holes in the bark?

Holes with stains or oozing liquid are a common sign of eucalyptus longhorned borers. Red ironbark is among the more resistant species, but any eucalyptus can be attacked when badly stressed. Deep soakings in long dry spells are the main defense.

When should I prune red ironbark?

Do routine pruning in December or January, when the borer beetles are not active. Avoid heavy pruning, which can sunburn newly exposed bark and leave the tree short of leaves. Remove borer-infested limbs as soon as you find them.

Can red ironbark grow near the coast?

Yes. It tolerates seaside conditions, and it has grown in Santa Monica since at least 1908. Coastal trees still need slow, deep soakings while young.

Will red ironbark grow in clay soil?

Yes, it tolerates clay soil. Clay holds water longer, so let it dry well between soakings. Waterlogged soil around the root crown invites Armillaria and Phytophthora root rots.

How cold can red ironbark get?

It is cold hardy to about 20 degrees F. Nights colder than that put it at risk of damage. In frost-prone gardens, choose a warm, sunny site.

More plant watering guides

Chaste TreeRoger's Red GrapeWhite Rain LilyDouble Knock Out RoseCat ThymeWhite IronbarkCast Iron PlantLeather Oak

Sources