WateringTimesWatering plan, $19
Apocynum cannabinum, WUCOLS IV

How often to water Indian hemp in California

In July in the Central Valley, established Indian hemp 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. Indian hemp, also called hemp dogbane, is a native perennial 2 to 6 feet tall that spreads by rhizomes into colonies. Flat-topped clusters of tiny greenish white flowers from late spring through summer draw many pollinators, then long, narrow pods release silky seeds. It grows in both damp and dry places, and all parts exude a toxic milky sap.

PerennialCalifornia nativeRated for 3 of 6 zones

How often to water Indian hemp, 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 Indian hemp 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 dry 3 inches down within the patch in summer signals Indian hemp needs water
  • Leaves drooping and yellowing early in a long dry spell can indicate thirst
  • Stems spreading well beyond the bed show rhizomes are running
  • Yellowing patches in waterlogged soil point to poor drainage

How to water it

  • Water the whole patch with a soaker, since it grows as a colony
  • Soak several inches down, then let the top few inches dry
  • Plant in full sun in sandy, well-drained soil
  • Contain it with a barrier or plant it where spreading is welcome
  • Leave dead stems standing 12 to 24 inches tall for nesting native bees

Through the seasons

Water new plants regularly as they spread. Established colonies take moderate summer water and handle dry spells. It flowers from late spring into late summer, then forms long pods with silky seeds. It dies back in winter, and dead stems left standing shelter native bees. WUCOLS rates Indian hemp moderate water on the north-central coast and in the Central Valley. In South Inland it carries a low water rating. WUCOLS has not evaluated it for the south coast, the high desert or the low desert.

In pots

Indian hemp can grow in a large pot, which keeps its rhizomes from taking over a bed. Use sandy, well-drained mix and water when the top couple of inches dry, letting it drain. In summer, check every couple of days. Empty the saucer. Wear gloves when handling it, since the sap is toxic. In winter, cut stems back and water lightly until spring growth.

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

Indian Hemp: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.370.4–0.31––
Feb0.530.65–0.35––
Mar0.871.09–0.52––
Apr1.181.52–0.64––
May1.462.08–0.78––
Jun1.612.48–0.92––
Jul1.612.67–1––
Aug1.492.39–0.93––
Sep1.241.8–0.74––
Oct0.871.18–0.53––
Nov0.470.56–0.36––
Dec0.310.34–0.27––
Year1217.11–7.37––

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 Indian hemp. 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 Indian hemp 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 Indian hemp, 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 Indian hemp in summer?

In July, established Indian hemp in loam needs a deep watering about every 5 days in the Central Valley and about every 14 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 Indian hemp need per day?

In July in the Central Valley, established Indian hemp 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 Indian hemp change across California?

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

Is Indian hemp poisonous?

Yes, all parts are considered highly toxic to people and mammals. It is believed to be poisonous to dogs. Wear gloves and keep pets away.

Does Indian hemp spread?

Yes, it spreads aggressively by rhizomes and can be weedy. Plant it where colonies are welcome or contain it. Pull runners promptly.

Is Indian hemp good for pollinators?

Yes, its small flowers attract many pollinators. Native bees also nest in its hollow dead stems. Leave some stems standing over winter.

Is Indian hemp native to California?

Yes, it grows across much of North America, including California. It is found in both damp and dry habitats. It suits native and pollinator gardens.

How do I propagate Indian hemp?

Sow seed or divide clumps. It also spreads on its own by rhizomes. Water new divisions until they root.

More plant watering guides

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Sources