How often to water allium in California
In July in the Central Valley, established allium needs about 1.9 gallons a week for a plant 2 feet across. Alliums are ornamental onions that grow from bulbs. They have narrow, grasslike leaves and round or flat-topped clusters of small star or cup-shaped flowers on bare stalks in spring. Many kinds are California natives or come from the Mediterranean, and all parts smell of onion. Most go dormant in summer, and wet soil then rots the bulbs.
How often to water allium, month by month
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.
How this is worked out: the plant’s WUCOLS rating times your city’s climate for the month, over the area the plant covers. Skip a watering after a good soaking rain.
How to tell it needs water
- Soil dry 2 inches down in spring while leaves are green signals allium needs water
- Leaves wilting before flowers open can indicate a dry spring
- Leaves yellowing and dying back at peak bloom is normal and signals summer rest
- Soft, rotting bulbs or white fuzzy growth at the base point to bulb rot from wet soil
How to water it
- Water from fall rains through spring bloom, while leaves are growing
- Soak several inches down, then let the top couple of inches dry
- Stop watering once leaves die back, and keep summer sprinklers away
- Plant bulbs in sun to part shade in loose soil with good to excellent drainage
- Divide crowded clumps from bulb offsets and replant at the same depth
Through the seasons
Most alliums grow through the cool, wet months, flower in spring, then rest in summer. Water only during that growing window if rain falls short. Leaves of most die back around peak bloom, and the bulbs want dry soil until fall. Some kinds self-sow. WUCOLS rates allium moderate water on the north-central coast, in the Central Valley and on the south coast. South Inland matches that moderate water rating. WUCOLS marks it as not suited to the high desert or the low desert.
In pots
Alliums grow well in deep pots of gritty, well-drained mix. Water when the top inch is dry while leaves are growing, letting excess drain. Empty the saucer. Once leaves wither after bloom, stop watering and keep the pot dry and shaded through summer. Resume watering when new shoots appear in fall or winter. Repot crowded bulbs while they are dormant.
- A year
- 17.11 gal per sq ft
- Reference
- Sacramento climate table
- Counts
- Plant need, before sprinkler losses
Monthly water need by climate zone
Allium: gallons per square foot per month, by WUCOLS climate zone
| Month | N. Coast | C. Valley | S. Coast | S. Inland | Hi Desert | Lo Desert |
|---|---|---|---|---|---|---|
| Jan | 0.37 | 0.4 | 0.78 | 0.78 | – | – |
| Feb | 0.53 | 0.65 | 0.81 | 0.87 | – | – |
| Mar | 0.87 | 1.09 | 1.15 | 1.3 | – | – |
| Apr | 1.18 | 1.52 | 1.4 | 1.61 | – | – |
| May | 1.46 | 2.08 | 1.61 | 1.95 | – | – |
| Jun | 1.61 | 2.48 | 1.74 | 2.29 | – | – |
| Jul | 1.61 | 2.67 | 1.98 | 2.51 | – | – |
| Aug | 1.49 | 2.39 | 1.86 | 2.33 | – | – |
| Sep | 1.24 | 1.8 | 1.49 | 1.86 | – | – |
| Oct | 0.87 | 1.18 | 1.15 | 1.33 | – | – |
| Nov | 0.47 | 0.56 | 0.84 | 0.9 | – | – |
| Dec | 0.31 | 0.34 | 0.65 | 0.68 | – | – |
| Year | 12 | 17.11 | 15.5 | 18.41 | – | – |
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 6
Rated moderate water in the Central Valley, like allium. Plants that drink alike can share one valve and one schedule.
CannasCanna spp.moderate water, Central Valley2.67 gal/sq ft in July
GladiolusGladiolus hybrids & selectionsmoderate water, Central Valley2.67 gal/sq ft in July
Spanish IrisIris xiphiummoderate water, Central Valley2.67 gal/sq ft in July
Creeping ButtercupRanunculus spp. (summer growing)moderate water, Central Valley2.67 gal/sq ft in July
Poppy AnemoneAnemone coronariamoderate water, Central Valley2.67 gal/sq ft in July
Persian CyclamenCyclamen persicum and hybrids (shade)moderate water, Central Valley2.67 gal/sq ft in JulySimilar plants that need less water 9
Rated lower than allium in the Central Valley. Worth a look for a new bed or a lawn replacement.
Star of BethlehemOrnithogalum arabicumlow water, Central Valley1.07 gal/sq ft in July
Ivy Leaf CyclamenCyclamen hederifoliumlow water, Central Valley1.07 gal/sq ft in July
Summer SnowflakeLeucojum aestivumlow water, Central Valley1.07 gal/sq ft in July
White Rain LilyZephyranthes candidalow water, Central Valley1.07 gal/sq ft in July
HyacinthHyacinthus spp.low water, Central Valley1.07 gal/sq ft in July
Sea SquillDrimia maritimalow water, Central Valley1.07 gal/sq ft in July
Naked LadyAmaryllis belladonnavery low water, Central Valley0.27 gal/sq ft in July
DaffodilNarcissus spp.very low water, Central Valley0.27 gal/sq ft in July
Giant ScillaScilla peruviana (Scilla hughii)very low water, Central Valley0.27 gal/sq ft in JulyTurn this into minutes on your water days
Every city page has a calculator that takes allium, 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 much should I water allium in summer?
In July, established allium needs about 1.9 gallons in the Central Valley, 1.4 gallons on the south coast and 1.8 gallons in the South Inland zone each week, for a plant 2 feet across. Water deeply and let the top of the soil dry before the next watering. Skip a watering after a soaking rain.
How much water does allium need per day?
In July in the Central Valley, established allium 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 allium change across California?
Yes. WUCOLS rates allium 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, moderate 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.
Why is my allium dying after it blooms?
Most alliums go dormant in summer, and leaves die back with peak bloom. That is normal. Stop watering and let the bulbs rest.
Are ornamental alliums edible?
Many ornamental onions are edible, though some are grown only for show. The genus carries a low poison rating. Confirm the species before eating any.
Why are my allium bulbs rotting?
Overly damp soil leads to bulb rot, white rot and other fungal problems. Improve drainage and stop summer watering. Plant in raised beds or slopes where clay holds water.
Do alliums spread?
Many form offsets and some self-sow. Divide offsets in spring for the best results. Some seed takes years to germinate.
Are there California native alliums?
Yes, many alliums are native to California. They follow the same pattern of winter growth and summer rest. Native kinds suit dry summer gardens.
More plant watering guides
Sources
- WUCOLS IV plant water use classification for Allium spp., the University of California survey California agencies use for landscape plan reviewRead August 23, 2026 on wucols.ucdavis.edu
- Model Water Efficient Landscape Ordinance, adopted text and appendices, effective 2025-01-02 · monthly reference evapotranspiration per city, Appendix CRead August 23, 2026 on water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/Water-Use-And-Efficiency/MWELO-Rulemaking/Final-MWELO-Text-and-Appendices_20250103.pdf
- UC Statewide IPM Program, irrigation scheduling using evapotranspirationRead September 30, 2026 on ipm.ucanr.edu/PMG/GARDEN/ENVIRON/evap.html
- Shaw and Pittenger, Landscape Irrigation System Evaluation and Management, UC Cooperative Extension, 2009Read September 30, 2026 on ucanr.edu/sites/default/files/2013-02/160836.pdf
- Pittenger, Water Management in Gardens and Landscapes, UC Riverside, 2017Read September 30, 2026 on ucanr.edu/sites/default/files/2017-03/258022.pdf