WateringTimesWatering plan, $19
Centaurea montana, WUCOLS IV

How often to water perennial cornflower in California

In July in the Central Valley, established perennial cornflower 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. Perennial cornflower, also called mountain bluet, is a spreading perennial from the mountains of Europe, 1 to 2 feet tall. From late spring into summer it carries rich blue flowers with fringed outer petals around reddish centers. It spreads by creeping stems and seed, likes sun and well-drained soil, and tolerates poor ground.

PerennialRated for 2 of 6 zones

How often to water perennial cornflower, 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 perennial cornflower 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

  • Leaves drooping in a hot spell while the soil is dry a few inches down mean the clump needs water
  • Mildew spots on the foliage by midsummer are a fungal problem this plant is prone to, not a water shortage
  • Stems flopping open in the middle of the clump call for staking or division, not extra water
  • Leaves yellowing and crowns softening in soil that stays wet point to overwatering, since it wants good drainage
  • Seedlings and rooted stems popping up around the clump are normal, and they multiply where the soil stays moist

How to water it

  • Water the base of the clump with drip or a soaker, wetting the soil 6 to 8 inches deep
  • Let the top couple of inches dry between waterings, since it handles dry to medium moisture
  • Plant in full sun or part shade in well-drained soil, even if that soil is poor
  • Cut the plant back after its first flush of flowers to renew the foliage and limit seeding
  • Divide clumps every 2 to 3 years, and keep water to the bed itself so runners stay in bounds

Through the seasons

Keep new plants moist until they root and start to spread. Established clumps flower from late spring into summer, and deadheading can bring a few more blooms in fall. The foliage dies back in winter, when rain usually covers its needs on the north-central coast and in the Central Valley. WUCOLS rates perennial cornflower low water on the north-central coast. In the Central Valley it rates moderate water. WUCOLS has not evaluated it for the south coast, South Inland, the high desert or the low desert.

In pots

Perennial cornflower grows well in a container, which also keeps its creeping stems and seedlings in check. Use a gritty, well-drained mix and a pot with drainage holes. Through hot weather, push a finger into the mix every second day and water when the first inch feels dry. Water until it drips from the base, and do not let the pot sit in standing water. Cut the plant back after its first bloom to keep it compact. In winter, once the foliage dies down, water only lightly.

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

Perennial Cornflower: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.150.4––––
Feb0.210.65––––
Mar0.351.09––––
Apr0.471.52––––
May0.582.08––––
Jun0.642.48––––
Jul0.642.67––––
Aug0.62.39––––
Sep0.51.8––––
Oct0.351.18––––
Nov0.190.56––––
Dec0.120.34––––
Year4.817.11––––

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 perennial cornflower. 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 perennial cornflower 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 perennial cornflower, 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 water does perennial cornflower need per day?

In July in the Central Valley, established perennial cornflower 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 perennial cornflower change across California?

Yes. WUCOLS rates perennial cornflower separately for each of the six California climate zones: low water in the North-Central Coastal zone, moderate water in the Central Valley zone, not evaluated in the South Coastal zone, not evaluated 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.

Does perennial cornflower spread?

Yes. It spreads by creeping stems and self-sows readily, especially where the soil stays moist. Deadhead after bloom to limit seedlings, and divide clumps every 2 to 3 years.

Should I cut back perennial cornflower after flowering?

Yes. Cutting it back after the first bloom renews the foliage and keeps seedlings down. Deadheading may also bring a few extra flowers in fall.

Why is my perennial cornflower flopping?

Its stems tend to sprawl, so the plant needs staking. Give it support early in the season, and divide old clumps in spring or fall.

What colors does perennial cornflower come in?

The species has rich blue flowers with reddish centers. Cultivars with white or pink flowers are also sold.

Can perennial cornflower grow in shade?

Yes. It grows in full sun or part shade, and it also suits coastal gardens.

More plant watering guides

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Sources