WateringTimesWatering plan, $19
Quillaja saponaria, WUCOLS IV

How often to water soapbark tree in California

In July in the Central Valley, established soapbark tree 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. Soapbark tree is a slender, upright evergreen from Chile with leathery oval leaves and drooping branchlets. Small, star-shaped flowers in late spring and summer are followed by pinwheel-shaped seed pods. It withstands drought once established but looks more lush with occasional deep watering, and its bark contains soapy saponins.

TreeRated for 3 of 6 zones

How often to water soapbark tree, 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 soapbark tree 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 8 inches down at the canopy edge tells you a soapbark tree has gone long enough without a soak
  • Thin, sparse foliage in a long dry summer suggests the tree could use an occasional deep watering
  • Leaves yellowing while the soil stays wet point to poor drainage or watering that comes too often
  • Frost-browned leaves after a cold snap in the low 20s show cold damage, not thirst
  • Lacewings and lady beetles on the flowers are welcome visitors, not a problem to treat

How to water it

  • Water a soapbark tree deeply and infrequently across the root zone with a soaker or drip ring
  • Wet the soil 18 to 24 inches down, then let it dry well before the next soak
  • Plant in full sun in average or poor soil that drains
  • Mulch the root area with wood chips, or plant it in a lawn where it shares deep irrigation
  • Extend the soaker as the narrow crown grows taller and wider

Through the seasons

Give a new soapbark tree regular deep soakings through its first two summers while roots spread. After that it can withstand drought, though occasional deep water keeps the foliage fuller. The tree is evergreen, flowers from late spring into summer, and the pinwheel fruit matures in fall. Prune young trees to develop a narrow, upright form. Winter rain usually covers the cool months on the coast and in the Central Valley. On the south coast, the north-central coast and in the Central Valley, WUCOLS rates soapbark tree low water. WUCOLS has not evaluated it for the high desert, the low desert or South Inland.

In pots

A young soapbark tree can grow in a large container for a few years, and its narrow form suits a patio. Use a deep pot with drainage holes and a well-drained mix. Check 2 to 3 inches down every few days in summer, and water deeply when dry. Empty the saucer after watering. The tree is hardy to the low 20s in the ground, but potted roots are more exposed, so shelter the pot in a hard freeze.

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
0.270.540.801.10.16JAN0.26FEB0.43MAR0.61APR0.83MAY0.99JUN1.07JUL0.95AUG0.72SEP0.47OCT0.22NOV0.14DEC0.270.540.801.10.16JFM0.61AMJ1.07JAS0.47OND
Gallons per square foot per month, Central Valley. Peak 1.07 in Jul, 6.84 a year.

Monthly water need by climate zone

Soapbark Tree: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.150.160.31–––
Feb0.210.260.32–––
Mar0.350.430.46–––
Apr0.470.610.56–––
May0.580.830.64–––
Jun0.640.990.69–––
Jul0.641.070.79–––
Aug0.60.950.74–––
Sep0.50.720.6–––
Oct0.350.470.46–––
Nov0.190.220.33–––
Dec0.120.140.26–––
Year4.86.846.2–––

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 soapbark tree. 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 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 JulyBlackwood AcaciaAcacia melanoxylonlow 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 soapbark tree, 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 soapbark tree in summer?

In July, established soapbark tree in loam needs a deep watering about every 20 days in the Central Valley and about every 27 days on the south coast. 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 soapbark tree need per day?

In July in the Central Valley, established soapbark tree 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 soapbark tree change across California?

Yes. WUCOLS rates soapbark tree 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, not evaluated in the South Inland zone, not evaluated in the High and Intermediate Desert zone, not evaluated in the Low Desert zone. The monthly table above shows how the same rating translates into different gallon amounts as reference evapotranspiration changes.

Why is it called soapbark?

Its bark contains saponins, foaming compounds long harvested in Chile. The name Quillaja comes from a native Chilean word meaning to wash. The saponins also make the plant potentially poisonous.

Can soapbark tree grow in a lawn?

Yes. It looks more lush when planted in an irrigated lawn, as long as the soil drains. Lawn watering may be more than it needs, so watch for yellowing leaves.

Is soapbark tree a good street tree?

Its narrow, columnar form suits confined spaces and streets, especially when shaped while young. Street trees still need deep watering until established.

How cold can soapbark tree take?

It is hardy to at least the low 20s. Colder snaps can brown the leaves, so protect young trees on the coldest nights.

Can you overwater soapbark tree?

Yes. It is native to dry, poor soils in Chile, so constantly wet ground is a poor fit. Water deeply, then let the soil dry well between soakings.

More plant watering guides

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Sources