WateringTimesWatering plan, $19
Iris sibirica, WUCOLS IV

How often to water Siberian iris in California

In July in the Central Valley, established Siberian iris in loam needs a deep watering about every 5 days: about 1.5 gallons each time for a plant 2 feet across, about 1.9 gallons a week. Siberian iris is a clumping perennial that grows from spreading rhizomes into a vase of slender, grassy leaves about 2 feet tall. In late spring and early summer it sends up beardless flowers marked with white or gold flashes. Most are blue-purple, but white, yellow and wine forms exist. It loves evenly moist soil and thrives at pond edges, though established clumps tolerate some drought.

PerennialRated for 3 of 6 zones

How often to water Siberian iris, 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 Siberian iris 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 an inch or two down in the clump signals that Siberian iris needs water, since it prefers evenly moist ground
  • Leaf tips browning in summer heat can indicate a dry root zone, especially in hot afternoon sun
  • Soft, collapsing rhizomes in soggy, airless soil can point to bacterial soft rot
  • Fewer flowers from a crowded clump call for division rather than more water
  • Sparse bloom after a mild winter reflects too little winter chill, not a watering problem

How to water it

  • Water across the whole clump with drip or a soaker line, keeping the soil evenly moist
  • Soak about 8 inches deep and water again before the top inch dries in summer
  • Plant in moist, fertile, organically rich soil that drains, or along a pond or stream edge
  • Give it full sun with some afternoon shade where summers run hot
  • Divide crowded clumps and keep new divisions moist for 6 to 8 weeks while they root

Through the seasons

Keep new plants and divisions moist through their first season. Established clumps want steady moisture from spring growth through bloom and summer, though they tolerate some drought after a season or two. Leaves die back in winter, and a cold winter rest improves the next spring's flowers. WUCOLS rates Siberian iris moderate water on the north-central coast and in the Central Valley, and high water on the south coast. It marks South Inland as not suited to it. WUCOLS has not evaluated it for the high desert or the low desert.

In pots

Siberian iris can grow in a large, deep container if the mix stays evenly moist. Use a rich, organic potting mix and a pot with drainage holes. In hot weather, check the mix daily and water before the top inch dries. Water until it drains, then empty the saucer. Divide the clump when it crowds the pot. After the leaves die back in late fall, keep the mix just damp and let the pot get winter cold, which helps flowering.

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
0.791.62.43.20.4JAN0.65FEB1.09MAR1.52APR2.08MAY2.48JUN2.67JUL2.39AUG1.8SEP1.18OCT0.56NOV0.34DEC0.791.62.43.20.4JFM1.52AMJ2.67JAS1.18OND
Gallons per square foot per month, Central Valley. Peak 2.67 in Jul, 17.11 a year.

Monthly water need by climate zone

Siberian Iris: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.370.41.24–––
Feb0.530.651.29–––
Mar0.871.091.84–––
Apr1.181.522.23–––
May1.462.082.58–––
Jun1.612.482.78–––
Jul1.612.673.17–––
Aug1.492.392.98–––
Sep1.241.82.38–––
Oct0.871.181.84–––
Nov0.470.561.34–––
Dec0.310.341.04–––
Year1217.1124.8–––

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 Siberian iris. Plants that drink alike can share one valve and one schedule.

DahliasDahlia spp.moderate water, Central Valley2.67 gal/sq ft in JulyFernsNephrolepis cordifolia (SHADE IN DESERT)moderate water, Central Valley2.67 gal/sq ft in JulyDayliliesHemerocallis spp. & cvs.moderate water, Central Valley2.67 gal/sq ft in JulyBegoniasBegonia & ssp. & cvs. (shade in the desert)moderate water, Central Valley2.67 gal/sq ft in JulyCalla LiliesZantedeschia aethiopica SHADE IN DESERTmoderate water, Central Valley2.67 gal/sq ft in JulySageSalvia officinalis and cvs.moderate water, Central Valley2.67 gal/sq ft in JulyBicolor MonkshoodAconitum cammarummoderate water, Central Valley2.67 gal/sq ft in JulyGarden MonkshoodAconitum napellusmoderate water, Central Valley2.67 gal/sq ft in JulyCarpet BugleAjuga reptans (shade)moderate water, Central Valley2.67 gal/sq ft in JulySnowdrop WindflowerAnemone sylvestrismoderate water, Central Valley2.67 gal/sq ft in JulyMountain SandwortArenaria montanamoderate water, Central Valley2.67 gal/sq ft in JulySwamp MilkweedAsclepias incarnatamoderate water, Central Valley2.67 gal/sq ft in JulyOrange MilkweedAsclepias tuberosamoderate water, Central Valley2.67 gal/sq ft in JulyGreater MasterwortAstrantia majormoderate water, Central Valley2.67 gal/sq ft in JulyHardy BegoniaBegonia grandismoderate water, Central Valley2.67 gal/sq ft in JulyWax BegoniaBegonia semperflorensmoderate water, Central Valley2.67 gal/sq ft in July

Similar plants that need less water 16

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

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 JulyIrisesIris germanicalow 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 July
Minutes for your sprinklers

Turn this into minutes on your water days

Every city page has a calculator that takes Siberian iris, 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 Siberian iris in summer?

In July, established Siberian iris in loam needs a deep watering about every 5 days in the Central Valley and about every 5 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 Siberian iris need per day?

In July in the Central Valley, established Siberian iris needs about 0.3 gallons a day for a plant 2 feet across and about 1.1 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 Siberian iris change across California?

Yes. WUCOLS rates Siberian iris separately for each of the six California climate zones: moderate water in the North-Central Coastal zone, moderate water in the Central Valley zone, high water in the South Coastal zone, not suited to this region 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 my Siberian iris not blooming?

Crowding, too much shade and warm winters can all cut flowering. It blooms best after a cold winter, so mild coastal gardens may see fewer flowers. Divide crowded clumps and give it more sun.

Can Siberian iris grow in wet soil?

Yes. It loves moisture and thrives near streams and pond edges where soil stays evenly moist. Avoid stagnant, airless mud, which can lead to rhizome rot.

When should I divide Siberian iris?

Divide clumps about every three years, or when they get crowded and bloom less. Cut the leaves back to 6 to 8 inches and keep at least two fans on each piece. Water the divisions well for 6 to 8 weeks.

Is Siberian iris toxic?

The rhizomes can cause stomach upset if eaten, and the sap can irritate skin. Wear gloves when dividing clumps.

How is Siberian iris different from bearded iris?

Its flowers are beardless and generally smaller than bearded iris blooms. Its leaves are narrow and grassy, forming a vase-shaped clump.

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Sources