WateringTimesWatering plan, $19
Syringa vulgaris, WUCOLS IV

How often to water common lilac in California

In July in the Central Valley, established common lilac in loam needs a deep watering about every 8 days: about 8.8 gallons each time for a plant 4 feet across, about 7.6 gallons a week. Common lilac is a deciduous shrub or small tree, 8 to 16 feet tall, grown for its fragrant spring flower clusters. It flowers best after a long, cold winter rest, which limits where it shines in California. Established plants want deep soakings with drying between them and do poorly in waterlogged ground.

ShrubRated for 4 of 6 zones

How often to water common 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 common 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 beneath the outer branches of an established lilac signals that it needs a deep soak
  • Leaves that stay limp into the evening over dry ground can indicate thirst during summer heat
  • A white, powdery film on summer leaves is mildew, a disease that extra water will not cure
  • Yellowing leaves and weak new shoots over soggy soil can indicate poor drainage, which lilac tolerates badly
  • New shoots crowding the base come from suckering roots or a rootstock, not from a watering change

How to water it

  • Water an established lilac in a wide ring beneath the outer branches rather than against the trunk
  • Soak the soil 12 to 18 inches deep, then let the upper several inches dry before watering again
  • Run drip emitters or a slow hose at soil level so water sinks in instead of running off
  • Plant in well-drained, neutral to alkaline soil, building a low mound where clay holds water
  • Widen the watered ring as the shrub spreads, and pull rootstock suckers on grafted plants

Through the seasons

Give a new lilac deep soakings through its first summer while roots spread. Established shrubs take deeper, wider spaced soakings. Flowers open in mid to late spring, and the leafy summer months are when irrigation matters most. After leaf fall the shrub rests and needs a long cold spell to ripen next year's buds, so mild winters reduce bloom. Late frost can kill opening buds. Winter rain usually supplies the dormant shrub on the north-central coast and in the Central Valley. High desert plants need checks in dry winters. WUCOLS rates common lilac low water on the north-central coast and moderate water in the Central Valley, South Inland and the high desert. WUCOLS marks it as not suited to the south coast or the low desert.

In pots

Common lilac is a big shrub, so a container suits a young plant or a compact cultivar for a few years. Use a wide, heavy pot with open drainage holes and a loose mix. Check the mix 2 inches down every few days in summer heat, and more often in valley sun. Water until excess drains away, then empty the saucer. After leaf fall, water lightly but do not let the mix dry out completely. Leave the pot outdoors in winter so the plant gets the cold rest it needs to flower.

1 Your climate zone six WUCOLS zones, each from its own reference city
2.67gal per sq ft in JulyModerate water use in the Central Valley zone
A year
17.11 gal per sq ft
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses
0.761.52.33.00.4JAN0.65FEB1.09MAR1.52APR2.08MAY2.48JUN2.67JUL2.39AUG1.8SEP1.18OCT0.56NOV0.34DEC0.761.52.33.00.4JFM1.52AMJ2.67JAS1.18OND
Gallons per square foot per month, Central Valley. Peak 2.67 in Jul, 17.11 a year.

Monthly water need by climate zone

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

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.150.4–0.780.74–
Feb0.210.65–0.870.93–
Mar0.351.09–1.31.46–
Apr0.471.52–1.611.89–
May0.582.08–1.952.39–
Jun0.642.48–2.292.85–
Jul0.642.67–2.513.04–
Aug0.62.39–2.332.79–
Sep0.51.8–1.862.14–
Oct0.351.18–1.331.46–
Nov0.190.56–0.90.93–
Dec0.120.34–0.680.65–
Year4.817.11–18.4121.27–

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 moderate water in the Central Valley, like common lilac. Plants that drink alike can share one valve and one schedule.

RosesRosa hybrids..bushmoderate water, Central Valley2.67 gal/sq ft in JulyAzaleasRhododendron spp. (CA native and non-native spp.)moderate water, Central Valley2.67 gal/sq ft in JulyCamelliasCamellia japonica (SHADE IN DESERT)moderate water, Central Valley2.67 gal/sq ft in JulyGardeniasGardenia spp. & cvs.moderate water, Central Valley2.67 gal/sq ft in JulyBird of ParadiseStrelitzia reginae (shade in desert)moderate water, Central Valley2.67 gal/sq ft in JulyHibiscusHibiscus rosa-sinensismoderate water, Central Valley2.67 gal/sq ft in JulySago PalmCycas revolutamoderate water, Central Valley2.67 gal/sq ft in JulyStar JasmineTrachelospermum jasminoides and cvs.moderate water, Central Valley2.67 gal/sq ft in JulyArborvitaeThuja occidentalis ssp. & cvs.moderate water, Central Valley2.67 gal/sq ft in JulyBambooBambusa spp.moderate water, Central Valley2.67 gal/sq ft in JulyLilacsSyringa hybrids (including Descanso hybrids)moderate water, Central Valley2.67 gal/sq ft in JulySpireaSpiraea spp. (CA native and non native spp.)moderate water, Central Valley2.67 gal/sq ft in JulyButterfly BushBuddleja davidii and hybridsmoderate water, Central Valley2.67 gal/sq ft in JulySageSalvia officinalis and cvs.moderate water, Central Valley2.67 gal/sq ft in JulyRed BuckeyeAesculus paviamoderate water, Central Valley2.67 gal/sq ft in JulyWestern ServiceberryAmelanchier alnifoliamoderate water, Central Valley2.67 gal/sq ft in July

Similar plants that need less water 16

Rated lower than common lilac in the Central Valley. Worth a look for a new bed or a lawn replacement.

LavenderLavandula spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyRosemaryRosmarinus officinalislow water, Central Valley1.07 gal/sq ft in JulyBougainvilleaBougainvillea & spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyOlive TreesOlea europaea 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 JulyLantanaLantana camara ssp. & cvs.low water, Central Valley1.07 gal/sq ft in JulySalviaSalvia greggii ssp., cvs. & hybridslow water, Central Valley1.07 gal/sq ft in JulyAloeAloe spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulySucculentsEcheveria spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyJunipersJuniperus spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyRussian SagePerovskia spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulySagebrushArtemisia spp. (shrubby)low water, Central Valley1.07 gal/sq ft in JulyWild PrivetLigustrum vulgarelow water, Central Valley1.07 gal/sq ft in JulyCoralberrySymphoricarpos orbiculatus (SHADE)low water, Central Valley1.07 gal/sq ft in JulySydney Golden WattleAcacia longifolialow water, Central Valley1.07 gal/sq ft in JulyBlue Leaf WattleAcacia salignalow 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 common 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 often should I water common lilac in summer?

In July, established common lilac in loam needs a deep watering about every 8 days in the Central Valley 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 common lilac need per day?

In July in the Central Valley, established common lilac needs about 1.1 gallons a day for a plant 4 feet across and about 4.3 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 common lilac change across California?

Yes. WUCOLS rates common lilac separately for each of the six California climate zones: low water in the North-Central Coastal zone, moderate water in the Central Valley zone, not suited to this region in the South Coastal zone, moderate water in the South Inland zone, moderate water in the High and Intermediate Desert zone, not suited to this region 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 my lilac not blooming in California?

Common lilac needs a long, cold winter rest to mature its flower buds, so warm winters cut bloom. Low chill cultivars flower more reliably in mild areas, though even they do best after a cold winter. A late frost can also kill buds that have begun to open.

Does powdery mildew mean my lilac needs more water?

No. The white coating is a fungal disease that often shows up on lilac leaves in summer. It spoils the look of the foliage but does little lasting harm. Thinning the center of the shrub improves airflow.

Why are shoots coming up around my lilac?

Common lilac spreads by suckering roots and can form a colony over time. On a grafted plant, the shoots may come from the rootstock instead. Cut unwanted suckers at the base early so they do not crowd the main stems.

Can you overwater lilac?

Yes. Lilac does poorly in soggy, poorly drained soil, where its roots sit wet and decline. Let the upper soil dry between soakings. Keep it away from a frequently watered lawn.

Will lilac grow in alkaline soil?

Yes. It tolerates neutral to alkaline soil and struggles in strongly acidic ground. In heavy clay, drainage is a bigger concern than pH.

More plant watering guides

Mugo PineCamphor TreeCreeping FigWhite ForsythiaPaperbark MapleSilver MapleJapanese BeautyberryEastern Dogwood

Sources