WateringTimesWatering plan, $19
Vitex trifolia 'Purpurea', WUCOLS IV

How often to water Arabian lilac in California

In July on the north-central coast, established Arabian lilac in loam needs a deep watering about every 13 days: about 8.8 gallons each time for a plant 4 feet across, about 4.6 gallons a week. Arabian lilac is a fast-growing evergreen to semi-evergreen shrub whose gray-green leaves turn up velvety purple undersides. Lavender flower spikes appear at the branch tips from summer into fall, sometimes into winter. Along the coast an established plant gets by on occasional deep soakings, while inland heat raises its needs.

ShrubRated for 2 of 6 zones

How often to water Arabian lilac, month by month

Your city
Plant width
4 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 Arabian lilac 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 the plant covers, 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 plant width

A shrub with its width marked from one side to the other and the circle under it shaded blue

Measure across the plant, from the tips of the leaves on one side to the tips on the other.

Water the whole area the plant covers, shown in blue. The gallons here cover that area.

A wider plant means more gallons each watering, not more waterings. While it is young, measure again each spring.

How to tell it needs water

  • Soil dry 4 to 6 inches down at the edge of the canopy signals that Arabian lilac needs a deep soak
  • Gray-green leaves that stay limp into the morning over dry soil can indicate thirst
  • A few older leaves dropping as new ones emerge is normal shedding, not a sign of drought
  • Sparse new growth through a hot inland summer can follow root zones that dry out between soakings
  • Leaves yellowing while the bed stays soggy for days suggest water is pooling around the roots

How to water it

  • Water Arabian lilac across its root zone with drip or a slow hose rather than a quick surface sprinkle
  • Wet the soil to about a foot and a half, then hold off until the upper few inches dry out
  • Plant it in full to part sun in well-drained soil, mounding the planting area where clay stays wet
  • Mulch beneath the spreading branches, keeping the mulch a few inches back from the trunk
  • Extend the watered ring as the shrub widens, since it can reach 10 to 15 feet across

Through the seasons

Water a new Arabian lilac deeply through its first summer, then widen the gaps between soakings as roots spread. Established shrubs stay leafy through mild winters, shedding older leaves as new ones push out. Flowering runs from summer into fall, and irrigation matters most through the dry warm months. Winter rain covers the cool months on the north-central coast and the south coast in most years. WUCOLS rates Arabian lilac moderate water on the north-central coast and low water on the south coast. WUCOLS has not evaluated it for the Central Valley, South Inland, the high desert or the low desert.

In pots

Arabian lilac makes a striking container shrub, but its fast growth fills a pot quickly. Give it a large pot with open drainage holes. In summer heat, feel the mix 2 inches down every few days and water when it is dry there. Let the excess flow out, then tip the saucer so roots do not sit wet. Trim it back occasionally to keep the top in proportion to the pot. Leaves can drop near 28 degrees and stems can be hurt near 25, so move a potted plant to shelter before a hard frost.

1 Your climate zone six WUCOLS zones, each from its own reference city
Not ratedWUCOLS does not rate Arabian Lilac for the Central Valley zone
A year
no figure
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses

WUCOLS lists Arabian Lilac as not evaluated for the Central Valley zone, so no monthly figure is computed here.

Monthly water need by climate zone

Arabian Lilac: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.37–0.31–––
Feb0.53–0.32–––
Mar0.87–0.46–––
Apr1.18–0.56–––
May1.46–0.64–––
Jun1.61–0.69–––
Jul1.61–0.79–––
Aug1.49–0.74–––
Sep1.24–0.6–––
Oct0.87–0.46–––
Nov0.47–0.33–––
Dec0.31–0.26–––
Year12–6.2–––

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 not evaluated in the Central Valley, like Arabian lilac. Plants that drink alike can share one valve and one schedule.

Formosa Sugar PalmArenga englerinot rated, Central Valleyno Central Valley ratingChilean Feather BambooChusquea culeou (C. breviglumis)not rated, Central Valleyno Central Valley ratingBlackbrushColeogyne ramosissimanot rated, Central Valleyno Central Valley ratingGlaucous Scorpion VetchCoronilla valentina glaucanot rated, Central Valleyno Central Valley ratingWillowleaf CotoneasterCotoneaster salicifoliusnot rated, Central Valleyno Central Valley ratingMadagascar SagoCycas thouarsii (SHADE)not rated, Central Valleyno Central Valley ratingIrish HeathDaboecia cantabricanot rated, Central Valleyno Central Valley ratingButterfly PalmDypsis lutescens (Areca)not rated, Central Valleyno Central Valley ratingUmbrella BambooFargesia murielaenot rated, Central Valleyno Central Valley ratingBlue Fountain BambooFargesia nitida (Sinarundinaria nitida) (BAMBOO)not rated, Central Valleyno Central Valley ratingPrickly HeathGaultheria mucronata (Pernettya mucronata)not rated, Central Valleyno Central Valley ratingOtterbossieGossypium harknessiinot rated, Central Valleyno Central Valley ratingBox-leaved HollyIlex crenatanot rated, Central Valleyno Central Valley ratingBellyache BushJatropha gossypiifolianot rated, Central Valleyno Central Valley ratingMountain LaurelKalmia latifolianot rated, Central Valleyno Central Valley ratingBarbados CherryMalpighia glabranot rated, Central Valleyno Central Valley rating
Minutes for your sprinklers

Turn this into minutes on your water days

Every city page has a calculator that takes Arabian lilac, 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 much water does Arabian lilac need per day?

In July on the north-central coast, established Arabian lilac needs about 0.7 gallons a day for a plant 4 feet across and about 2.6 gallons a day for a plant 8 feet across. Give it in deep waterings spread days apart rather than a little every day, so the whole root zone gets wet.

Does watering for Arabian lilac change across California?

Yes. WUCOLS rates Arabian lilac separately for each of the six California climate zones: moderate water in the North-Central Coastal zone, not evaluated 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 are my Arabian lilac leaves purple underneath?

That is its normal look: gray-green above and velvety purple below. Leaf color does not signal thirst, so judge water by soil moisture and leaf firmness. Crushed leaves give off a peppery scent.

Does Arabian lilac self-seed?

It can self-sow and turn weedy. Pull seedlings while they are small, and keep the shrub away from wild land. Watering only the shrub's own root zone also gives stray seedlings less help.

How cold can Arabian lilac take?

It stays evergreen to about 28 degrees, its stems survive to about 25, and its roots to at least 20. A plant that loses leaves to frost uses less water until it regrows. Feel the soil before soaking it.

Can Arabian lilac take wind and heat?

It tolerates windy sites and inland heat. Both dry the soil faster, so check moisture more often in exposed spots. A layer of mulch helps hold water between soakings.

Should I prune Arabian lilac?

It grows fast and gets big, so give it room and trim it back from time to time. Trimming brings flushes of fresh growth. Check the soil as each new flush develops.

Can you overwater Arabian lilac?

Yes. It is grown in well-drained soil, and constantly wet ground invites root problems. Let the top few inches dry before the next soak, especially near the coast where it gets by on less.

More plant watering guides

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Sources