WateringTimesWatering plan, $19
Osmunda regalis, WUCOLS IV

How often to water royal fern in California

In July in the Central Valley, established royal fern 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. Royal fern is a large deciduous fern that builds a clump of broad, airy fronds. The fertile fronds carry rusty brown spore clusters at their tips that look like flowers. In the wild it grows along streams and in bogs, sometimes in standing water, and it wants soil that never dries out.

PerennialRated for 3 of 6 zones

How often to water royal fern, 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 royal fern 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 even an inch down beside a royal fern crown means it needs water now, since this fern grows in wet ground
  • Frond edges browning and crisping in summer sun warrant a soil check and possibly more shade
  • Fronds wilting at midday on a sunny site suggest the roots cannot keep up with the heat
  • Yellow fronds over wet soil seldom mean overwatering in this bog fern, so look at sun and heat first
  • Fronds turning yellow and then red-brown in fall mark the start of dormancy, not thirst

How to water it

  • Water at the base of the clump with a soaker line or slow hose, wetting the soil well beyond the crown
  • Keep the root zone moist about a foot deep, watering again as soon as the surface begins to dry
  • Plant in rich, acidic soil packed with compost or leaf mold, which holds moisture around the fibrous roots
  • Site it in part shade or dappled light, giving it more sun only where the ground stays wet, such as a pond edge
  • Mulch the bed thickly with leaf mold and widen the watered area as the clump expands

Through the seasons

A newly planted royal fern needs constantly moist soil through its first year while the crown roots in. Established clumps still need wet or evenly moist soil from spring until the fronds color in fall. In winter the plant is dormant, and winter rain covers the cool months on the coast and in the Central Valley. Resume watering when the fiddleheads unroll in spring. WUCOLS rates royal fern high water on the north-central coast, in the Central Valley and on the south coast. WUCOLS has not evaluated it for South Inland, and marks it as not suited to the high desert or the low desert.

In pots

Royal fern can grow in a large pot or a container water garden, since it tolerates soggy soil. Check the mix every few days in mild weather and daily in summer heat, and never let it dry through. Unlike most potted plants, it tolerates a little water left in the saucer during summer heat. Use a rich, peaty mix and a pot wide enough for the spreading clump. In fall the fronds die back, so empty the saucer and keep the dormant crown barely moist until 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

Royal Fern: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.60.641.24–––
Feb0.841.041.29–––
Mar1.391.741.84–––
Apr1.882.432.23–––
May2.333.322.58–––
Jun2.583.972.78–––
Jul2.584.273.17–––
Aug2.383.822.98–––
Sep1.982.882.38–––
Oct1.391.881.84–––
Nov0.740.891.34–––
Dec0.50.551.04–––
Year19.227.3824.8–––

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 high water in the Central Valley, like royal fern. 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 royal fern 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 royal fern, 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 royal fern in summer?

In July, established royal fern in loam needs a deep watering about every 3 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 royal fern need per day?

In July in the Central Valley, established royal fern 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 royal fern change across California?

Yes. WUCOLS rates royal fern 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, not evaluated 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 royal fern grow in standing water?

Yes. Stream banks and bogs are its natural home, and it sometimes grows with its base in standing water. A pond margin or rain garden suits it, as long as that water does not vanish in summer.

Can royal fern take full sun?

Only with constant moisture, and best where summers stay cool. In most California gardens, give it part shade or dappled light. A wet pond edge lets it handle more sun.

Why is it called flowering fern?

The rusty brown spore clusters at the tips of fertile fronds look like flower spikes. It does not truly flower. Those brown tips are normal and do not mean the frond has dried out.

Why are my royal fern fronds turning brown in fall?

Royal fern is deciduous, and its fronds turn yellow to red-brown before dying back. That is normal dormancy. Water less once the fronds are down, but do not let the bed dry out completely.

How do I divide royal fern?

Divide it in early spring or in fall. Keep a crown with roots on each piece and soak the divisions right after planting. Keep them constantly moist while they reroot.

More plant watering guides

Ornamental RhubarbWeeping WillowPeking WillowWillowSteviaDelphiniumCoast RedwoodVariegated Sweet Flag

Sources