WateringTimesWatering plan, $19
Acorus gramineus, WUCOLS IV

How often to water Japanese sweet flag in California

In July in the Central Valley, established Japanese sweet flag in loam needs a deep watering about every 3 days: about 1.5 gallons each time for a plant 2 feet across, about 3.0 gallons a week. Japanese sweet flag is a grasslike perennial from East Asia that forms fans of narrow, glossy leaves about a foot tall, spreading slowly by rhizomes. It grows in very wet soil or partly submerged at pond edges. Dry soil quickly scorches the leaf tips, so steady moisture is the whole secret.

PerennialRated for 4 of 6 zones

How often to water Japanese sweet flag, 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 Japanese sweet flag 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 surface feeling dry to the touch around the clump in summer signals Japanese sweet flag needs water
  • Leaf tips turning brown and crisp point to soil that has been allowed to dry
  • Fans losing their upright stance and splaying open can indicate thirst in hot sun
  • Yellowing in hot afternoon sun even in wet soil suggests it needs more shade

How to water it

  • Keep the root zone constantly moist with drip, a soaker, or a bog setting
  • Water before the surface dries, especially in summer heat
  • Plant along streams, ponds and bog gardens, or in a low spot that stays wet
  • Give it afternoon shade in hot summer areas
  • Space plants 8 to 12 inches apart so rhizomes can fill in

Through the seasons

Keep a new planting wet from day one, and never let established clumps dry out. Summer heat is when it needs the most attention, especially away from the coast, where afternoon shade also helps. It is evergreen to semi-evergreen and keeps its fans through winter, when rain and cool weather ease the load. Along the north-central coast and the south coast, and inland through the Central Valley and South Inland, WUCOLS assigns Japanese sweet flag a high water rating. Neither desert is a fit: WUCOLS marks it as not suited to the high desert or the low desert.

In pots

Japanese sweet flag works in a pot only if the mix never dries. Use a moisture-holding mix and stand the pot in a saucer or tray of water during summer. Check daily in heat and top up the water. A pot can also be set at a pond edge with its rim just above the water. In winter, keep the mix moist but empty a saucer that stays cold and stagnant. Divide crowded clumps in spring.

1 Your climate zone six WUCOLS zones, each from its own reference city
4.27gal per sq ft in JulyHigh water use in the Central Valley zone
A year
27.38 gal per sq ft
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses
1.12.13.24.30.64JAN1.04FEB1.74MAR2.43APR3.32MAY3.97JUN4.27JUL3.82AUG2.88SEP1.88OCT0.89NOV0.55DEC1.12.13.24.30.64JFM2.43AMJ4.27JAS1.88OND
Gallons per square foot per month, Central Valley. Peak 4.27 in Jul, 27.38 a year.

Monthly water need by climate zone

Japanese Sweet Flag: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.60.641.241.24––
Feb0.841.041.291.39––
Mar1.391.741.842.08––
Apr1.882.432.232.58––
May2.333.322.583.12––
Jun2.583.972.783.67––
Jul2.584.273.174.02––
Aug2.383.822.983.72––
Sep1.982.882.382.98––
Oct1.391.881.842.13––
Nov0.740.891.341.44––
Dec0.50.551.041.09––
Year19.227.3824.829.46––

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 high water in the Central Valley, like Japanese sweet flag. Plants that drink alike can share one valve and one schedule.

Red GingerAlpinia purpuratahigh water, Central Valley4.27 gal/sq ft in JulyShell GingerAlpinia zerumbethigh water, Central Valley4.27 gal/sq ft in JulySiberian BuglossBrunnera macrophyllahigh water, Central Valley4.27 gal/sq ft in JulyMarsh MarigoldCaltha palustrishigh water, Central Valley4.27 gal/sq ft in JulyUmbrella Sedge and PapyrusCyperus spp. (CA native and non-native species)high water, Central Valley4.27 gal/sq ft in JulyUmbrella PlantDarmera peltata (Peltiphyllum)high water, Central Valley4.27 gal/sq ft in JulyFoxgloveDigitalis purpurea cvshigh water, Central Valley4.27 gal/sq ft in JulyLeopard PlantFarfugium japonicum cvs. (Ligularia tussilaginea cvs.)high water, Central Valley4.27 gal/sq ft in JulyTransvaal DaisyGerbera jamesonii & hybridshigh water, Central Valley4.27 gal/sq ft in JulyGiant GunneraGunnera manicatahigh water, Central Valley4.27 gal/sq ft in JulyWhite Ginger LilyHedychium coronariumhigh water, Central Valley4.27 gal/sq ft in JulyJapanese IrisIris ensatahigh water, Central Valley4.27 gal/sq ft in JulyRushJuncus aquatic spp. (native and non-native spp.)high water, Central Valley4.27 gal/sq ft in JulyCardinal FlowerLobelia cardinalis hybrids and cvs. (CA native and non-native spp.)high water, Central Valley4.27 gal/sq ft in JulyBananaMusa spp. (shade in low desert)high water, Central Valley4.27 gal/sq ft in JulySensitive FernOnoclea sensibilishigh water, Central Valley4.27 gal/sq ft in July

Similar plants that need less water 16

Rated lower than Japanese sweet flag in the Central Valley. Worth a look for a new bed or a lawn replacement.

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
Minutes for your sprinklers

Turn this into minutes on your water days

Every city page has a calculator that takes Japanese sweet flag, 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 Japanese sweet flag in summer?

In July, established Japanese sweet flag in loam needs a deep watering about every 3 days in the Central Valley, about every 5 days on the south coast and about every 4 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 Japanese sweet flag need per day?

In July in the Central Valley, established Japanese sweet flag needs about 0.4 gallons a day for a plant 2 feet across and about 1.7 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 Japanese sweet flag change across California?

Yes. WUCOLS rates Japanese sweet flag separately for each of the six California climate zones: high water in the North-Central Coastal zone, high water in the Central Valley zone, high water in the South Coastal zone, high water in the South Inland zone, not suited to this region 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.

Can Japanese sweet flag grow in a pond?

Yes, it grows in partly submerged conditions at pond and stream edges. Keep the crown near the waterline rather than deep under it. It also does well in boggy soil.

Why are my sweet flag tips brown?

Leaf scorch from dry soil is the usual cause. Keep the soil constantly moist. Give it afternoon shade in hot areas.

Can Japanese sweet flag take full sun?

It grows in full sun to part shade where soil stays wet. In hot summer areas it does best with afternoon shade. Sun dries soil faster, so check more often.

Is Japanese sweet flag a grass?

No, it only looks grasslike. It belongs to the sweet flag family. Its spring flowers are insignificant.

Are there gold or striped sweet flags?

Yes, selections such as 'Ogon' have yellow leaves, and others are striped white or yellow. All need the same wet soil.

More plant watering guides

White Ginger LilyClimbing HydrangeaSnowball HydrangeaLacecap HydrangeaJapanese IrisRushBrazilian Plume FlowerCardinal Flower

Sources