WateringTimesWatering plan, $19
Gunnera manicata, WUCOLS IV

How often to water giant gunnera in California

In July in the Central Valley, established giant gunnera 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. Giant gunnera is a huge herbaceous perennial from Brazil with rough, deeply veined leaves up to 6 feet across on prickly stalks. Conical spikes of reddish-green flowers rise around the base in late spring. It is a high water plant that needs constantly damp soil and sun or light shade, and it grows poorly anywhere dry. Plants sold under this name are often a look-alike hybrid.

PerennialRated for 4 of 6 zones

How often to water giant gunnera, 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 giant gunnera 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 turning dry around the crown in summer signals giant gunnera needs water right away
  • Huge leaves wilting at midday and failing to recover by evening can indicate a dry root zone
  • Leaf edges browning and crisping in sun and wind can follow even a short dry spell
  • Small, sparse leaves through the summer point to dry soil or deep shade

How to water it

  • Keep the root zone constantly wet with drip, soakers or a bog setting
  • Water before the surface dries, especially in summer heat
  • Plant at a pond edge or low spot in sun or light shade
  • Mulch over the crown in winter to protect it from frost
  • Leave plenty of room, since each leaf can span several feet

Through the seasons

Keep a new gunnera wet from planting, and never let established plants dry out in the warm months. It is herbaceous, dying back in winter and sending up new leaves in spring. Frost can damage the crown, so mulch over it for winter. Hot, dry wind is hard on the huge leaves, so a sheltered spot helps. WUCOLS rates giant gunnera high water on the north-central coast, in the Central Valley, on the south coast and in South Inland. WUCOLS marks it as not suited to the high desert or the low desert.

In pots

Giant gunnera is too large for most containers, but a young plant can grow in a very large tub of rich, moisture-holding mix. Keep the mix wet at all times, standing the tub in a tray of water through summer. Check daily in heat. In winter, as the leaves die back, keep the mix damp and cover the crown with mulch against frost. Divide a crowded tub 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

Giant Gunnera: 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 giant gunnera. 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 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 giant gunnera 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 giant gunnera, 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 giant gunnera in summer?

In July, established giant gunnera 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 giant gunnera need per day?

In July in the Central Valley, established giant gunnera 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 giant gunnera change across California?

Yes. WUCOLS rates giant gunnera 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.

How big does giant gunnera get?

Its leaves can reach about 3 to 6 feet across on stout, prickly stalks. A mature clump needs a lot of room. Plan for a wide, constantly wet planting area.

Why are my gunnera leaves small?

Gunnera grows poorly on dry soil or in deep shade. Keep the soil constantly damp and give it sun or light shade. Leaves size up as moisture improves.

How do I protect gunnera in winter?

Frost can damage the crown. Cover it with a thick layer of mulch. Keep the soil damp, not flooded.

Is my plant really giant gunnera?

Many plants sold under this name turn out to be a hybrid with the closely related Chilean gunnera. The two look very similar. Both need the same constant moisture.

Can giant gunnera grow in a dry garden?

No, it needs permanently damp soil. It grows poorly on dry soil. Plant it only where a pond, stream or bog keeps the soil wet.

More plant watering guides

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Sources