WateringTimesWatering plan, $19
Iris germanica, WUCOLS IV

How often to water irises in California

In July in the Central Valley, established irises in loam need a deep watering about every 14 days: about 1.5 gallons each time for a plant 2 feet across, about 0.8 gallons a week. This guide follows bearded iris, which grows from a thick rhizome at or just below the soil surface. Roots beneath it need moisture, while the rhizome is vulnerable to rot in soggy ground. Read the soil as well as the leaf fans before deciding a fading clump needs water.

PerennialRated for 6 of 6 zones

How often to water irises, month by month

Your city
Plant width
2 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 irises 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 foot 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 2 to 3 inches down beside a leaf fan signals that bearded iris needs a moisture check
  • Papery outer leaves can be normal aging, so browning alone does not establish thirst
  • Short stalks or shriveled buds can accompany dryness, crowding, shade or heat, so check the soil before increasing irrigation
  • A soft, foul-smelling rhizome or a leaf fan that pulls loose can indicate rot
  • Leaves yellowing from the fan base over wet soil warrant a drainage check rather than another soak

How to water it

  • Water beside the fans, keeping rhizomes near the surface with up to an inch of soil cover in extreme heat
  • Moisten soil about a foot deep beside established iris rhizomes, then let the upper soil dry before watering again
  • Use drip or a slow hose around the clump to keep water out of the leaf fans
  • Keep mulch off rhizomes and place it only on open soil between clumps
  • Use a mound or raised bed in heavy clay and widen coverage as the clump spreads into a ring

Through the seasons

Keep soil around newly planted iris roots lightly moist through the first warm season as they anchor. Established clumps use most water while leaves and flower stalks grow in late winter and spring, and as roots develop in fall. Growth slows after bloom in hot weather, so reduce water without stopping all soil checks. Coastal and Central Valley rain can supply cool-season moisture; check both deserts through dry winter spells. WUCOLS rates bearded iris low water on the north-central coast, in the Central Valley and on the south coast. It rates moderate water in South Inland, the high desert and the low desert.

In pots

Bearded iris needs a freely draining pot with space for roots below the surface rhizome. Choose a container at least 12 inches wide and deep. Feel the mix beside the rhizome a couple of inches down during California heat. Water when dry there, letting excess leave the drainage holes, then empty the saucer. Reduce irrigation after flowering without letting the roots dry completely. Shelter pots from prolonged winter soaking and keep checking during dry spells.

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

Irises: 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 irises. Plants that drink alike can share one valve and one schedule.

AgapanthusAgapanthus orientalislow water, Central Valley1.07 gal/sq ft in JulyGeraniumsPelargonium x hortorum and cvs.low water, Central Valley1.07 gal/sq ft in JulySalviaSalvia greggii ssp., cvs. & hybridslow water, Central Valley1.07 gal/sq ft in JulySucculentsEcheveria spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyRussian SagePerovskia spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyYarrowAchillea millefolium (non-native hybrids)low water, Central Valley1.07 gal/sq ft in JulyMountain AlyssumAlyssum montanumlow water, Central Valley1.07 gal/sq ft in JulySilver SageSalvia argentealow water, Central Valley1.07 gal/sq ft in JulyPurple MulleinVerbascum phoeniceumlow water, Central Valley1.07 gal/sq ft in JulySilvery YarrowAchillea clavennaelow water, Central Valley1.07 gal/sq ft in JulyFern Leaf YarrowAchillea filipendulinalow water, Central Valley1.07 gal/sq ft in JulyCalifornia Native YarrowAchillea millefolium (CA native cultivars)low water, Central Valley1.07 gal/sq ft in JulyWoolly YarrowAchillea tomentosalow water, Central Valley1.07 gal/sq ft in JulyPerennial HollyhockAlcea rosea cvs.low water, Central Valley1.07 gal/sq ft in JulyMountain Lady's MantleAlchemilla alpinalow water, Central Valley1.07 gal/sq ft in JulyLady's MantleAlchemilla mollislow 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 irises, 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 irises in summer?

In July, established irises in loam need a deep watering about every 14 days in the Central Valley, about every 18 days on the south coast and about every 6 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 do irises need per day?

In July in the Central Valley, established irises need about 0.1 gallons a day for a plant 2 feet across and about 0.4 gallons a day for a plant 4 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 irises change across California?

Yes. WUCOLS rates irises 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.

How do I water newly divided iris rhizomes?

Water thoroughly at planting to settle soil around the trimmed roots. Keep the root zone lightly moist while new growth develops. Late-summer divisions may need temporary shade as well as water; do not assume winter rain has already arrived.

Why does water run off a crowded iris pot?

A pot packed with rhizomes can shed water before it reaches the roots. Check below the rhizomes after a slow soaking. Divide and repot a crowded clump to restore room for mix and roots.

Do iris bulbs need the same watering?

Dutch iris grows from bulbs below ground and follows a different planting rhythm. It grows through winter and spring, then needs dry soil after foliage yellows into dormancy. The bearded iris ratings here should not be transferred to bulbous irises.

Should I water bearded iris after flowering?

Reduce irrigation gradually while keeping the green fans. Those leaves support new growth after the flowers are gone. Remove spent stalks and let the soil dry well between soakings.

What should I do with a rotting iris rhizome?

Remove softened tissue with a clean knife and disinfect the blade between cuts. Expose the remaining rhizome to air and check drainage. Resume watering according to soil moisture rather than keeping the clump continuously damp.

More plant watering guides

Silver WattleGreen WattleSydney Golden WattleBlackwood AcaciaBlue Leaf WattleSilvery YarrowFern Leaf YarrowCalifornia Native Yarrow

Sources