WateringTimesWatering plan, $19
Eucalyptus rudis, WUCOLS IV

How often to water flooded gum in California

In July in the Central Valley, established flooded gum 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. Flooded gum, also called desert gum, is a fast-growing eucalyptus from streambanks and seasonally flooded ground in southwestern Australia. Its bark turns rough and fibrous with age, and its adult leaves are slightly glossy and sickle-shaped. It accepts periodic flooding and tolerates drought, but drought stress worsens redgum lerp psyllid, a pest that infests it heavily in California.

TreeRated for 6 of 6 zones

How often to water flooded gum, 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 flooded gum 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 flooded gum's root ball means it is ready for a slow soak
  • Whitish, caplike covers on the leaves, above sticky and sooty ground, are the work of redgum lerp psyllid
  • Early leaf drop in a dry summer can follow psyllid feeding, drought stress or both, and a deep soak helps with either
  • Topsoil that stays soggy around the trunk base after watering invites the root rots eucalyptus are prone to

How to water it

  • Soak a young flooded gum over its root ball, then widen the wet ring as the crown spreads toward 40 feet
  • Place drip emitters or a slow soaker beneath the outer canopy of an established tree, well away from the trunk
  • Water slowly and deeply rather than with the frequent, shallow sprinkling used on lawns
  • Let the topsoil dry between soakings so the root crown never stays wet for long
  • Leave nitrogen fertilizer off the root zone, because excess nitrogen pushes the soft shoots psyllids prefer

Through the seasons

Water a young flooded gum deeply through its first summers, widening the wet area as the roots spread. Established trees tolerate drought. Still, this streambank species gains from a deep soak now and then through long summer and fall droughts, which also keeps psyllid numbers down. It is evergreen. Winter rain covers the cool months on the coast and in the Central Valley, while desert trees need soil checks in dry winters. Along the north-central coast, in the Central Valley, on the south coast and in South Inland, WUCOLS rates flooded gum low water. In the high desert and the low desert, the rating rises to moderate water.

In pots

Flooded gum grows fast into a tree 20 to 60 feet tall, so keep a seedling in a container only until planting time. Use a deep pot with open holes in the base and a gritty, free-draining mix. In summer heat, push a finger 2 inches into the mix every few days and water once that depth is dry. Water until it drains, then empty the saucer. In winter, water only when the mix is dry. Watch new shoots for psyllid caps and honeydew, since females lay eggs on young leaves and drought stress worsens the damage. Get it into the ground before its roots coil.

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

Flooded Gum: 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 flooded gum. 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 flooded gum, 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 flooded gum in summer?

In July, established flooded gum 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 flooded gum need per day?

In July in the Central Valley, established flooded gum 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 flooded gum change across California?

Yes. WUCOLS rates flooded gum 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.

What is the sticky mess under my flooded gum?

It is most likely honeydew from redgum lerp psyllid, which can infest flooded gum heavily in California. Black sooty mold grows on the honeydew, and heavy infestations make the tree drop leaves early. Deep soaks that keep the tree out of drought stress reduce psyllid numbers.

Is flooded gum the same as Eucalyptus grandis?

No. Eucalyptus grandis, the rose gum, is also called flooded gum, but this guide covers Eucalyptus rudis from southwestern Australia. Pest tables use the name for both, so check the botanical name before applying advice. Eucalyptus rudis is the flooded gum most infested by redgum lerp psyllid.

Can flooded gum take wet soil?

Yes. It grows wild on streambanks and seasonally flooded ground, and it accepts periodic flooding. Irrigation that keeps the topsoil soggy around the trunk is another matter, since it is susceptible to Armillaria and Phytophthora root rots. Let the surface dry between soakings.

Should I fertilize flooded gum?

Usually not. Eucalyptus rarely need nitrogen to grow well, and extra nitrogen produces the succulent new shoots that psyllid nymphs and egg-laying females prefer. Keep lawn and shrub fertilizer out of the root zone too.

When should I prune flooded gum?

Remove dead or hazardous branches whenever they appear. Do other pruning in December or January in southern California, or from November through March in the north. Borer adults are inactive then, and moisture stress is low. Pruning pushes soft new growth that psyllids favor, so keep cuts light.

Does flooded gum handle wind and salt?

Yes. It tolerates salt, wind and poor soils, and its wind resistance is rated medium high. On an exposed site, keep watering a young tree deeply until it is established.

More plant watering guides

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Sources