WateringTimesWatering plan, $19
Albizia julibrissin, WUCOLS IV

How often to water silk tree in California

In July in the Central Valley, established silk 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. Silk tree, often sold as mimosa, is a fast-growing, wide-spreading deciduous tree with feathery leaves and fluffy, fragrant pink flowers in early summer. It needs summer heat to bloom well. Once rooted it copes with dry spells in coastal and valley gardens, but it is often short lived and reseeds freely.

TreeRated for 6 of 6 zones

How often to water silk 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 silk 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 4 inches down under the outer branches of a young silk tree means it is time to water
  • Leaves yellowing and dropping in midsummer on a young tree, with dry soil below, point to thirst
  • Wilting and leaf drop on one limb after another while the soil is moist can mean Fusarium wilt, a lethal disease of this tree
  • Leaves turning yellow while the ground stays soggy point to root rot, which this tree is also prone to
  • Fine webbing and skeletonized leaves in summer come from mimosa webworm, not from dry soil

How to water it

  • Water a young silk tree over its root ball and a ring beyond it, widening the ring as the low branches spread
  • Soak slowly to about 18 inches, then allow the top few inches to dry before the next watering
  • Set emitters under the outer canopy of an older tree rather than against the trunk
  • Plant in soil that drains well, away from heavy, wet ground where root rot takes hold
  • Rake fallen flowers, leaves and pods off drip lines so water still reaches the soil

Through the seasons

Water a new silk tree deeply through its first summer or two, then taper off as roots spread. Established trees bloom from about May into July and set flat seed pods that can hang on through winter. Leaves drop in fall, and the bare tree needs little water until spring. Rain usually covers the dormant months on the coast and in the Central Valley. WUCOLS rates silk tree low water on the north-central coast, in the Central Valley and on the south coast. Moderate water is the rating for South Inland, the high desert and the low desert, where summer heat raises its needs.

In pots

A young silk tree or a compact cultivar can live in a big container for a few seasons. In summer, probe the mix 2 to 3 inches down every couple of days, and daily when desert heat sets in. Give it a slow soak until water escapes the drainage holes, and do not leave water sitting in the saucer. Fast growth fills a pot with roots quickly, so a tree that wilts soon after watering needs more room. Once the leaves fall, water the bare tree only when the mix has dried.

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

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

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.150.160.310.780.740.78
Feb0.210.260.320.870.930.93
Mar0.350.430.461.31.461.52
Apr0.470.610.561.611.891.95
May0.580.830.641.952.392.45
Jun0.640.990.692.292.852.79
Jul0.641.070.792.513.042.85
Aug0.60.950.742.332.792.6
Sep0.50.720.61.862.142.08
Oct0.350.470.461.331.461.49
Nov0.190.220.330.90.930.96
Dec0.120.140.260.680.650.68
Year4.86.846.218.4121.2721.08

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 silk 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 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 silk 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 silk tree in summer?

In July, established silk tree 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 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 silk tree need per day?

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

Yes. WUCOLS rates silk 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, moderate 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.

Why are my silk tree's leaves closing?

The leaflets fold up at night and when touched, which is normal. Closed leaves in the evening do not mean the tree is thirsty. Check the soil only if leaves droop or yellow during the day.

Is silk tree invasive?

It reseeds freely and has become invasive in the southeastern United States. Sterile cultivars such as 'Merlot Majik' and 'Summer Chocolate' reseed far less. Pull any seedlings while they are small.

Why is my silk tree dying?

Fusarium wilt is a common and lethal disease of silk tree, and it causes wilting even in moist soil. The tree is also short lived, with an average life span of about 30 years. Extra water will not save a tree with wilt.

Are silk tree seeds poisonous?

Yes. The seeds contain a toxin that can harm dogs and livestock. Rake up fallen pods where dogs play.

How messy is a silk tree?

Very. It sheds flowers in summer, then leaves and seed pods, so expect clean-up for months. Keep it away from pools and patios, and clear litter from drip emitters.

Does silk tree need full sun?

It grows in sun or part shade but needs summer heat to flower well. A cool, shaded spot gives fewer blooms. Plants in shade also dry out more slowly, so check the soil before watering.

More plant watering guides

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Sources