WateringTimesWatering plan, $19
Sagina subulata (Arenaria), WUCOLS IV

How often to water Irish moss in California

In July in the Central Valley, established Irish moss in loam needs a deep watering about every 8 days: about 2.2 gallons each time for a plant 2 feet across, about 1.9 gallons a week. Irish moss is a low, evergreen groundcover in the carnation family that forms a dense, mossy mat of slender stems rooting at the nodes. Tiny white flowers dot it in spring. It prefers cool, moist conditions and moderately fertile, rocky or sandy soil, and it struggles in intense heat and drought. Overwatering can also be a problem.

Ground coverPerennialRated for 4 of 6 zones

How often to water Irish moss, 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 Irish moss 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 1.5 feet 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

  • A mat that feels dry when you press a finger into the soil beneath in summer means Irish moss needs water
  • Patches turning brown in a hot, dry spell point to drought and heat stress
  • Mat browning and thinning in soggy soil points to too much water
  • Small new colonies appearing nearby come from its own seed

How to water it

  • Water lightly and often enough to keep the soil just moist
  • Let the surface dry slightly between waterings
  • Plant in sun with some midday shade, in rocky or sandy soil
  • Use it between stepping stones and in paving gaps
  • Keep it out of spots that stay soggy

Through the seasons

Water new plantings often enough to keep the soil moist while stems root. Established mats want steady moisture in summer and some midday shade inland, but not soggy soil. Most growth comes in cool, moist spring weather, and it reseeds into small colonies. Irish moss gets a moderate water rating from WUCOLS along the north-central coast, in the Central Valley and on the south coast. South Inland carries a high water rating. Both desert zones are marked not suited.

In pots

Irish moss looks charming in shallow bowls, troughs and between pot feet, where its mossy mounds soften hard edges. Use a sandy, well-drained mix. Water when the surface just starts to dry, letting it drain. In summer, shallow containers can need water daily, so check often and give midday shade. Never let the pot sit in water. In winter, water only when the mix dries.

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
1.02.03.04.00.4JAN0.65FEB1.09MAR1.52APR2.08MAY2.48JUN2.67JUL2.39AUG1.8SEP1.18OCT0.56NOV0.34DEC1.02.03.04.00.4JFM1.52AMJ2.67JAS1.18OND
Gallons per square foot per month, Central Valley. Peak 2.67 in Jul, 17.11 a year.

Monthly water need by climate zone

Irish Moss: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.370.40.781.24––
Feb0.530.650.811.39––
Mar0.871.091.152.08––
Apr1.181.521.42.58––
May1.462.081.613.12––
Jun1.612.481.743.67––
Jul1.612.671.984.02––
Aug1.492.391.863.72––
Sep1.241.81.492.98––
Oct0.871.181.152.13––
Nov0.470.560.841.44––
Dec0.310.340.651.09––
Year1217.1115.529.46––

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 moderate water in the Central Valley, like Irish moss. Plants that drink alike can share one valve and one schedule.

DahliasDahlia spp.moderate water, Central Valley2.67 gal/sq ft in JulyStar JasmineTrachelospermum jasminoides and cvs.moderate water, Central Valley2.67 gal/sq ft in JulyHoneysuckleLonicera japonicamoderate 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 JulyIvyHedera helixmoderate water, Central Valley2.67 gal/sq ft in JulyCalla LiliesZantedeschia aethiopica SHADE IN DESERTmoderate water, Central Valley2.67 gal/sq ft in JulyStrawberriesFragaria spp. & cvs. (CA native and non-natives species)moderate 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 JulyGreen Supreme ManzanitaArctostaphylos uva-ursi 'Green Supreme'moderate water, Central Valley2.67 gal/sq ft in JulyMassachusetts ManzanitaArctostaphylos uva-ursi 'Massachusetts'moderate water, Central Valley2.67 gal/sq ft in July

Similar plants that need less water 16

Rated lower than Irish moss in the Central Valley. Worth a look for a new bed or a lawn replacement.

BougainvilleaBougainvillea & spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyAgapanthusAgapanthus orientalislow water, Central Valley1.07 gal/sq ft in JulyGeraniumsPelargonium x hortorum and cvs.low water, Central Valley1.07 gal/sq ft in JulyLantanaLantana camara ssp. & 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 JulyJunipersJuniperus 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 JulySagebrushArtemisia spp. (shrubby)low 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 July
Minutes for your sprinklers

Turn this into minutes on your water days

Every city page has a calculator that takes Irish moss, 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 Irish moss in summer?

In July, established Irish moss in loam needs a deep watering about every 8 days in the Central Valley, about every 11 days on the south coast and about every 5 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 Irish moss need per day?

In July in the Central Valley, established Irish moss 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 Irish moss change across California?

Yes. WUCOLS rates Irish moss separately for each of the six California climate zones: moderate water in the North-Central Coastal zone, moderate water in the Central Valley zone, moderate 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 Irish moss take foot traffic?

It tolerates light to moderate foot traffic. It is ideal between stepping stones. Do not use it for heavy play areas.

Why is my Irish moss turning brown?

Heat and drought brown it, but so does overwatering. Check the soil before watering. Give it midday shade inland.

Is Irish moss a real moss?

No, it is a flowering plant in the carnation family with moss-like leaves. It has tiny white flowers. It spreads by rooting stems and seed.

Does Irish moss need sun?

It grows best in full sun with some midday shade. Hot inland sun stresses it. Cool coastal gardens suit it.

What pests bother Irish moss?

It is generally disease and pest free. Aphids can appear. Good drainage prevents most problems.

More plant watering guides

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Sources