WateringTimesWatering plan, $19
Eryngium maritimum, WUCOLS IV

How often to water sea holly in California

In July in the Central Valley, established sea holly 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. Sea holly is a clump-forming perennial from European coastal sand dunes, with stiff, waxy, spiny blue-green leaves. Thistle-like blue flower heads sit in collars of spiky bracts. It wants full sun and sharp, sandy drainage. Rich soil, shade and soggy ground are its enemies, and wet roots rot.

PerennialRated for 4 of 6 zones

How often to water sea holly, 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 sea holly 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 beside the clump in summer means sea holly can take a soak
  • Lower leaves browning and flower heads shriveling early in a long hot spell can point to a dry root zone
  • A clump that collapses at the base over wet, heavy soil points to root rot
  • A white powdery film on the leaves is powdery mildew, so judge soil moisture separately
  • Soft, lanky growth with weak stems can point to soil that is too rich or too wet

How to water it

  • Water at the base of the clump, soaking about a foot deep, then let the soil dry before the next round
  • Plant in full sun in sandy or gravelly soil that drains fast, skipping compost and rich amendments
  • Mulch with gravel rather than bark so the crown stays dry
  • Water sparingly once it is established on the south coast and in South Inland
  • Water early in the day so any wet leaves dry quickly

Through the seasons

Water a new sea holly regularly while it roots in, then let the soil dry between soakings. Blue flower heads appear from spring through late summer and last a long time, on the plant or cut and dried. Established clumps need deep but infrequent soakings in dry weather. Winter rain covers the cool months on the coast and in the Central Valley, so add nothing then. Its WUCOLS rating is moderate water for the Central Valley and the north-central coast. South Inland and the south coast rate low water. WUCOLS has not evaluated it for the low desert or the high desert.

In pots

Sea holly grows well in a deep pot of sandy, gritty mix that drains fast. In summer, test the mix with a finger every few days and wait until the top 2 inches feel dry. Soak it thoroughly, let the excess pour out, and never leave the pot standing in a saucer, since wet mix rots the crown. Full sun suits it in a container too. In winter, water only lightly, and move the pot out of steady rain if the mix stays wet.

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
0.671.32.02.70.4JAN0.65FEB1.09MAR1.52APR2.08MAY2.48JUN2.67JUL2.39AUG1.8SEP1.18OCT0.56NOV0.34DEC0.671.32.02.70.4JFM1.52AMJ2.67JAS1.18OND
Gallons per square foot per month, Central Valley. Peak 2.67 in Jul, 17.11 a year.

Monthly water need by climate zone

Sea Holly: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.370.40.310.31––
Feb0.530.650.320.35––
Mar0.871.090.460.52––
Apr1.181.520.560.64––
May1.462.080.640.78––
Jun1.612.480.690.92––
Jul1.612.670.791––
Aug1.492.390.740.93––
Sep1.241.80.60.74––
Oct0.871.180.460.53––
Nov0.470.560.330.36––
Dec0.310.340.260.27––
Year1217.116.27.37––

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 sea holly. 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 sea holly 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 sea holly, 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 sea holly in summer?

In July, established sea holly in loam needs a deep watering about every 5 days in the Central Valley, about every 18 days on the south coast and about every 14 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 sea holly need per day?

In July in the Central Valley, established sea holly 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 sea holly change across California?

Yes. WUCOLS rates sea holly separately for each of the six California climate zones: moderate water in the North-Central Coastal zone, moderate water in the Central Valley zone, low water in the South Coastal zone, low water 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 sea holly grow at the beach?

Yes. It grows wild on coastal sand dunes and shingle and makes a good seaside plant. Sandy, windy spots suit it as long as it gets full sun.

Can I dry sea holly flowers?

Yes. The flower heads last a long time and can be cut and dried for winter arrangements. Wear gloves, since the bracts are spiny.

Why is my sea holly rotting?

Wet, heavy or rich soil is the usual cause, since it grows naturally in sand. Move it to a raised bed or gravel garden and water less often.

Does sea holly need fertilizer?

No. Very fertile, rich soil does not suit it, and lean, sandy ground does. Skip feeding and compost.

How do I grow sea holly in clay soil?

Clay holds too much water for this dune plant. Build a raised bed or mound with sand and gravel, and water only once the top 2 inches are dry.

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Sources