WateringTimesWatering plan, $19
Rheum palmatum var. tanguticum, WUCOLS IV

How often to water ornamental rhubarb in California

In July in the Central Valley, established ornamental rhubarb 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. Ornamental rhubarb is a big rhizomatous perennial from China with jagged, deeply cut leaves that open dark reddish purple in late spring and mature to deep green with red undersides. In summer, branching stems up to 6 feet tall carry clusters of tiny white, pink or deep red flowers. It needs deep, moist, fertile soil and plenty of room.

PerennialRated for 2 of 6 zones

How often to water ornamental rhubarb, 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 ornamental rhubarb 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 inches down near the crown during summer signals ornamental rhubarb needs water
  • Huge leaves collapsing at midday and staying limp into evening can indicate thirst
  • Leaf edges browning and crisping in hot sun can follow a dry root zone
  • A soft, rotting crown in waterlogged soil points to crown rot

How to water it

  • Water around the crown with a soaker or slow hose, keeping water off the crown itself
  • Wet the soil about a foot deep, and water again before the surface dries out
  • Plant in deep, moist, fertile soil, ideally in sun
  • Mulch with organic matter in early spring
  • Give it ample space, since the leaves spread wide

Through the seasons

Keep a new plant evenly moist from spring through summer. Established clumps still want deep, moist soil throughout the growing season. It is deciduous, with leaves emerging in late spring and dying back in fall. Cut back faded leaves at the end of the season, and divide clumps in early spring. WUCOLS rates ornamental rhubarb moderate water on the north-central coast. In the Central Valley it carries a high water rating. WUCOLS has not evaluated it for the south coast, South Inland, the high desert or the low desert.

In pots

Ornamental rhubarb is a large plant for a container, but a young one can grow in a very big tub of rich mix. Keep the mix moist, watering when the top inch dries and letting it drain well. In warm weather it may need water daily. Empty the saucer. Cut faded leaves and flower spikes at season's end. In winter, while it is dormant, keep the mix barely damp.

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

Ornamental Rhubarb: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.370.64––––
Feb0.531.04––––
Mar0.871.74––––
Apr1.182.43––––
May1.463.32––––
Jun1.613.97––––
Jul1.614.27––––
Aug1.493.82––––
Sep1.242.88––––
Oct0.871.88––––
Nov0.470.89––––
Dec0.310.55––––
Year1227.38––––

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 ornamental rhubarb. Plants that drink alike can share one valve and one schedule.

Japanese Sweet FlagAcorus gramineushigh water, Central Valley4.27 gal/sq ft in JulyRed 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 July

Similar plants that need less water 16

Rated lower than ornamental rhubarb 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 ornamental rhubarb, 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 ornamental rhubarb need per day?

In July in the Central Valley, established ornamental rhubarb 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 ornamental rhubarb change across California?

Yes. WUCOLS rates ornamental rhubarb separately for each of the six California climate zones: moderate water in the North-Central Coastal zone, high water in the Central Valley zone, not evaluated 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.

Can I eat ornamental rhubarb?

No, it is grown as an ornamental and is harmful if eaten. Keep pets away from it. Wear gloves when handling.

How big does ornamental rhubarb get?

It can reach about 5 to 8 feet tall and wide in flower. The leaves alone are very large. Give it plenty of room.

Why is my rhubarb crown rotting?

Crown rot follows waterlogged soil. Keep water off the crown and improve drainage. Mulch around, not over, the crown.

When should I divide ornamental rhubarb?

Divide it in early spring as growth begins. Replant pieces in deep, fertile soil. Keep them moist while they settle.

What pests affect ornamental rhubarb?

Slugs and black aphids can feed on it. Check leaves early in the season. Damage is not a sign it needs water.

More plant watering guides

Blood Twig DogwoodUmbrella Sedge and PapyrusUmbrella PlantFoxgloveRed-veined EnkianthusAbyssinian BananaEuropean BeechLeopard Plant

Sources