WateringTimesWatering plan, $19
Euphorbia milii, WUCOLS IV

How often to water crown of thorns in California

In July in the Central Valley, established crown of thorns in loam needs a deep watering about every 20 days: about 8.8 gallons each time for a plant 4 feet across, about 3.0 gallons a week. Crown of thorns is a spiny succulent shrub from Madagascar, grown for tiny flowers framed by long-lasting bracts in red, pink, yellow or white. It handles dry soil well and blooms through the warm season. Cold, wet soil is its main enemy, so water deeply only after the ground or mix has dried.

ShrubSucculentRated for 4 of 6 zones

How often to water crown of thorns, month by month

Your city
Plant width
4 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 crown of thorns 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

  • Soil dry 2 to 3 inches down beside the stems in summer means a plant in the ground is ready for water
  • Leaves dropping during a hot, dry spell while the plant is still in bloom can mean it needs a deeper soak
  • Some leaf drop in late fall, ahead of the winter rest, is normal and does not call for more water
  • Soft, blackened stems near the soil line over damp ground point to stem or root rot
  • Sparse bracts in a hot inland summer can mean the plant wants midday shade and a little more moisture

How to water it

  • Water at the base of the plant, soaking the root area while keeping the spiny stems dry
  • Let the soil dry 2 to 3 inches down between summer soakings, and give very little water during the winter rest
  • Plant in sandy or rocky soil with sharp drainage, or in a raised bed where the ground is clay
  • Give it midday shade in South Inland and low desert gardens so it keeps flowering through the heat
  • Use a thin layer of gravel around the stems instead of an organic mulch that stays damp

Through the seasons

Keep a new crown of thorns lightly moist while it roots in, then let the soil dry between soakings. Established plants flower through the warm months and need summer water mainly in hot, dry spells. Some leaves drop before the winter rest, when the plant needs very little water and dislikes cold, wet soil. On the south coast and in the Central Valley, winter rain usually supplies all it needs. WUCOLS rates crown of thorns low water in the Central Valley, on the south coast, in South Inland and in the low desert. WUCOLS marks it as not suited to the north-central coast or the high desert.

In pots

Crown of thorns does very well in a pot, outdoors in summer or indoors by a bright window. Use a sandy, fast-draining mix in a pot with a drainage hole. In summer heat, check the mix every few days and water once the top inch or two is dry. Soak until water runs out, then empty the saucer. During the winter rest, after some leaves fall, water sparingly and keep the pot above 35 degrees F and out of cold rain.

1 Your climate zone six WUCOLS zones, each from its own reference city
1.07gal per sq ft in JulyLow water use in the Central Valley zone
A year
6.84 gal per sq ft
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses
0.280.570.851.10.16JAN0.26FEB0.43MAR0.61APR0.83MAY0.99JUN1.07JUL0.95AUG0.72SEP0.47OCT0.22NOV0.14DEC0.280.570.851.10.16JFM0.61AMJ1.07JAS0.47OND
Gallons per square foot per month, Central Valley. Peak 1.07 in Jul, 6.84 a year.

Monthly water need by climate zone

Crown of Thorns: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan–0.160.310.31–0.31
Feb–0.260.320.35–0.37
Mar–0.430.460.52–0.61
Apr–0.610.560.64–0.78
May–0.830.640.78–0.98
Jun–0.990.690.92–1.12
Jul–1.070.791–1.14
Aug–0.950.740.93–1.04
Sep–0.720.60.74–0.83
Oct–0.470.460.53–0.6
Nov–0.220.330.36–0.38
Dec–0.140.260.27–0.27
Year–6.846.27.37–8.43

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 low water in the Central Valley, like crown of thorns. Plants that drink alike can share one valve and one schedule.

LavenderLavandula spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyRosemaryRosmarinus officinalislow water, Central Valley1.07 gal/sq ft in JulyBougainvilleaBougainvillea & spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyOlive TreesOlea europaea ssp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyCrape MyrtleLagerstroemia spp., hybrids & 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 JulyAloeAloe spp. & cvs.low 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 JulySagebrushArtemisia spp. (shrubby)low water, Central Valley1.07 gal/sq ft in JulyWild PrivetLigustrum vulgarelow water, Central Valley1.07 gal/sq ft in JulyCoralberrySymphoricarpos orbiculatus (SHADE)low water, Central Valley1.07 gal/sq ft in JulySydney Golden WattleAcacia longifolialow water, Central Valley1.07 gal/sq ft in JulyBlue Leaf WattleAcacia salignalow 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 crown of thorns, 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 crown of thorns in summer?

In July, established crown of thorns in loam needs a deep watering about every 20 days in the Central Valley, about every 27 days on the south coast and about every 22 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 crown of thorns need per day?

In July in the Central Valley, established crown of thorns needs about 0.4 gallons a day for a plant 4 feet across and about 1.7 gallons a day for a plant 8 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 crown of thorns change across California?

Yes. WUCOLS rates crown of thorns separately for each of the six California climate zones: not suited to this region in the North-Central Coastal zone, low water in the Central Valley zone, low water in the South Coastal zone, low water in the South Inland zone, not suited to this region in the High and Intermediate Desert zone, low water in the Low Desert zone. The monthly table above shows how the same rating translates into different gallon amounts as reference evapotranspiration changes.

Is crown of thorns sap dangerous?

Yes. The milky sap irritates skin and can damage eyes, and chewing the plant can blister the mouth. Wear gloves and eye protection when you prune it, and keep it away from children and pets.

Why is my crown of thorns dropping leaves?

Some leaf drop before the winter rest is normal. Leaves also fall when the soil stays cold and wet, so check drainage before adding water. New leaves come only on new stem growth in spring.

Why is my crown of thorns not blooming?

Give it more sun, since it flowers best in full sun along the south coast. In hot inland gardens, midday shade and steadier moisture improve the bloom. A plant resting in winter may pause until warm weather returns.

Can crown of thorns grow outdoors in California?

Yes, where frost is rare. It dislikes temperatures below 35 degrees F. Cover a plant in the ground on cold nights, or grow it in a pot you can move. It also makes a good seaside plant.

Why do bugs stick to my crown of thorns flowers?

The flower stalks are sticky and sometimes trap gnats, but the plant is not carnivorous. Trapped insects do not mean it needs more or less water.

More plant watering guides

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Sources