WateringTimesWatering plan, $19
Lobelia siphilitica, WUCOLS IV

How often to water great blue lobelia in California

In July on the north-central coast, established great blue lobelia in loam needs a deep watering about every 6 days: about 1.5 gallons each time for a plant 2 feet across, about 1.8 gallons a week. Great blue lobelia is a clumping perennial from stream banks, swamps and wet meadows of eastern North America. Stiff, leafy stalks carry spikes of blue tubular flowers from late summer into early fall. It wants rich soil that stays moist all season. Dry soil is what sets it back, not wet ground.

PerennialRated for 2 of 6 zones

How often to water great blue lobelia, 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 great blue lobelia 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 that feels dry just an inch or two down beside the clump means great blue lobelia needs water now
  • Lance-shaped leaves drooping in the morning, before the sun reaches them, point to a root zone that has dried out
  • Leaves that sicken while the soil stays soggy call for a look at other causes, since this lobelia tolerates wet soil
  • Ragged holes and slime trails on the leaves point to snails and slugs, which favor the damp ground this plant needs

How to water it

  • Water great blue lobelia at the base of the clump with a soaker hose or drip, keeping the soil evenly moist
  • Soak the root zone well, then check again before the top inch has a chance to dry out
  • Spread a layer of compost or leaf mulch around the clump to hold moisture, keeping it off the crown
  • Plant it in rich, humusy soil in part shade, such as the damp edge of a pond, stream or rain garden
  • Widen the watered area as the clump grows or as seedlings fill in around it

Through the seasons

Keep a new great blue lobelia evenly moist through its first season while it settles. Established clumps still need constant moisture, so this is not a plant to leave dry between soakings. It grows through spring, then blooms from late summer into early fall. The stalks die back for winter and new growth returns in spring. Winter rain covers the cool months on the coast while the clump rests. WUCOLS rates great blue lobelia high water on the north-central coast. It rates moderate water on the south coast. WUCOLS has not evaluated it for the Central Valley, South Inland, the high desert or the low desert.

In pots

Great blue lobelia can grow in a pot if the mix never dries out. Use a deep container with rich, moisture-holding mix and drainage holes. Check the top inch every day or two in summer, and daily when the pot sits in afternoon sun. Water until it drains from the holes. Move the pot into part shade during south coast heat, since sun dries it fast. After the stalks die back in fall, keep the mix lightly damp through winter rather than wet or bone dry.

1 Your climate zone six WUCOLS zones, each from its own reference city
Not ratedWUCOLS does not rate Great Blue Lobelia for the Central Valley zone
A year
no figure
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses

WUCOLS lists Great Blue Lobelia as not evaluated for the Central Valley zone, so no monthly figure is computed here.

Monthly water need by climate zone

Great Blue Lobelia: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.6–0.78–––
Feb0.84–0.81–––
Mar1.39–1.15–––
Apr1.88–1.4–––
May2.33–1.61–––
Jun2.58–1.74–––
Jul2.58–1.98–––
Aug2.38–1.86–––
Sep1.98–1.49–––
Oct1.39–1.15–––
Nov0.74–0.84–––
Dec0.5–0.65–––
Year19.2–15.5–––

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 not evaluated in the Central Valley, like great blue lobelia. Plants that drink alike can share one valve and one schedule.

Lilyleaf LadybellsAdenophora liliifolianot rated, Central Valleyno Central Valley ratingArnicaArnica montananot rated, Central Valleyno Central Valley ratingFrilly BergeniaBergenia ciliatanot rated, Central Valleyno Central Valley ratingCabbage on a StickBrighamia insignisnot rated, Central Valleyno Central Valley ratingBasket PlantCallisia fragransnot rated, Central Valleyno Central Valley ratingForest SedgeCarex sylvaticanot rated, Central Valleyno Central Valley ratingUmbrella DracaenaDianella ensifolianot rated, Central Valleyno Central Valley ratingRusty FoxgloveDigitalis ferrugineanot rated, Central Valleyno Central Valley ratingBig-Flowered FoxgloveDigitalis grandifloranot rated, Central Valleyno Central Valley ratingWoolly FoxgloveDigitalis lanatanot rated, Central Valleyno Central Valley ratingSunset FoxgloveDigitalis obscuranot rated, Central Valleyno Central Valley ratingMale FernDryopteris filix-masnot rated, Central Valleyno Central Valley ratingAlpine Sea HollyEryngium alpinumnot rated, Central Valleyno Central Valley ratingPurple SpurgeEuphorbia dulcisnot rated, Central Valleyno Central Valley ratingQueen of the MeadowFilipendula ulmarianot rated, Central Valleyno Central Valley ratingDropwortFilipendula vulgaris (Filipendula hexapetala)not rated, Central Valleyno Central Valley rating
Minutes for your sprinklers

Turn this into minutes on your water days

Every city page has a calculator that takes great blue lobelia, 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 great blue lobelia need per day?

In July on the north-central coast, established great blue lobelia needs about 0.3 gallons a day for a plant 2 feet across and about 1.0 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 great blue lobelia change across California?

Yes. WUCOLS rates great blue lobelia separately for each of the six California climate zones: high water in the North-Central Coastal zone, not evaluated in the Central Valley zone, moderate water 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 great blue lobelia need full sun?

No. It takes full sun only in cool climates or where the soil stays wet. In most California gardens, part shade suits it better. Afternoon shade helps the soil hold moisture.

Can great blue lobelia grow in a rain garden?

Yes. It naturally grows along streams, in swamps and in low wet meadows. Plant it in the wetter, lower part of a rain garden. The drier rim suits it less.

Is great blue lobelia poisonous?

Yes, it is listed as poisonous. Keep children and pets from chewing on it. Plant it away from play areas.

Does great blue lobelia spread?

It forms clumps and can self-seed into colonies where conditions suit it. Divide crowded clumps in spring. Water new divisions until they root.

What pollinators visit great blue lobelia?

Bumblebees and other long-tongued bees are the main visitors. Hummingbirds and butterflies also come to the blue flowers. The flowers open in late summer and carry on into early fall.

Is great blue lobelia native to California?

No. It is native to eastern North America. It grows in California gardens with steady moisture, but it is not a local wildflower.

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Sources