WateringTimesWatering plan, $19
Alnus rubra (Alnus oregona), WUCOLS IV

How often to water red alder in California

In July in the Central Valley, established red alder in loam needs a deep watering about every 5 days: about 55 gallons each time under a 10 foot canopy, about 76 gallons a week. Red alder is a fast-growing native deciduous tree of coastal streams and moist forests. It has smooth, mottled grayish-white bark and an open, airy crown of bright green leaves. It fixes its own nitrogen and tolerates salty, brackish water, poor drainage and seasonal flooding. It needs plenty of water and grows best near the coast.

TreeCalifornia nativeRated for 4 of 6 zones

How often to water red alder, month by month

Your city
Canopy width
10 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 red alder 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 under the branches, 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 canopy width

A tree with its canopy width marked across the widest branches and the circle under it shaded blue

Measure across the branches, from the tips of the outer leaves on one side to the tips on the other. A tape works, or pace it out.

Water the whole circle under the branches, shown in blue. The gallons here cover that circle.

A wider canopy means more gallons each watering, not more waterings. While the tree is young, measure again each spring.

How to tell it needs water

  • Soil dry 4 inches down beneath the canopy in summer signals that a red alder needs a deep soak
  • Leaves yellowing and dropping early in summer heat point to a root zone that has dried out
  • White powdery patches on the leaves point to powdery mildew rather than thirst
  • A thinning crown with honey-colored mushrooms at the base warrants a check for root rot
  • Leaves chewed to lace point to caterpillars, not water stress

How to water it

  • Water generously over the whole root zone with a soaker hose or drip, since this tree grows along streams
  • Keep the top 18 inches of soil moist through the dry season, watering again as soon as the surface dries
  • Plant it near the coast or in a low, damp spot such as a bioswale or the edge of a retention basin
  • Keep it well away from foundations, paving and pipes, since its root damage potential is high
  • Mulch the root zone with leaf litter and widen the watered area as the slender crown rises

Through the seasons

A newly planted red alder needs steady, generous water through its first summers while its roots spread. Established trees away from streams still need deep summer irrigation. Leaves come out in spring and drop in fall, and winter rain covers the leafless months on the coast and in the Central Valley. Its stems can freeze below about 15 degrees. WUCOLS rates red alder high water on the north-central coast, in the Central Valley, on the south coast and in South Inland. The high desert and the low desert are marked not suited.

In pots

Red alder grows too fast and too large to stay in a container for long. A young tree can wait a season in a deep pot, but check the mix daily in summer heat, since it needs constant moisture. Water until it drains through, and a little water left in the saucer does it no harm in summer. Plant it out in fall or winter so rain can help it establish. Shelter a potted tree if temperatures fall toward 15 degrees.

1 Your climate zone six WUCOLS zones, each from its own reference city
4.27gal per sq ft in JulyHigh water use in the Central Valley zone
A year
27.38 gal per sq ft
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses
1.12.13.24.30.64JAN1.04FEB1.74MAR2.43APR3.32MAY3.97JUN4.27JUL3.82AUG2.88SEP1.88OCT0.89NOV0.55DEC1.12.13.24.30.64JFM2.43AMJ4.27JAS1.88OND
Gallons per square foot per month, Central Valley. Peak 4.27 in Jul, 27.38 a year.

Monthly water need by climate zone

Red Alder: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.60.641.241.24––
Feb0.841.041.291.39––
Mar1.391.741.842.08––
Apr1.882.432.232.58––
May2.333.322.583.12––
Jun2.583.972.783.67––
Jul2.584.273.174.02––
Aug2.383.822.983.72––
Sep1.982.882.382.98––
Oct1.391.881.842.13––
Nov0.740.891.341.44––
Dec0.50.551.041.09––
Year19.227.3824.829.46––

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 high water in the Central Valley, like red alder. Plants that drink alike can share one valve and one schedule.

Big Leaf MapleAcer macrophyllumhigh water, Central Valley4.27 gal/sq ft in JulyWhite AlderAlnus rhombifoliahigh water, Central Valley4.27 gal/sq ft in JulyRiver BirchBetula nigrahigh water, Central Valley4.27 gal/sq ft in JulyWater BirchBetula occidentalishigh water, Central Valley4.27 gal/sq ft in JulyEuropean White BirchBetula pendulahigh water, Central Valley4.27 gal/sq ft in JulyWhite-Barked Himalayan BirchBetula utilis var. jacquemontiihigh water, Central Valley4.27 gal/sq ft in JulyEuropean BeechFagus sylvaticahigh water, Central Valley4.27 gal/sq ft in JulyBlack CottonwoodPopulus trichocarpa (Populus balsamifera)high water, Central Valley4.27 gal/sq ft in JulyCarolina PoplarPopulus x canadensishigh water, Central Valley4.27 gal/sq ft in JulyWeeping WillowSalix babylonicahigh water, Central Valley4.27 gal/sq ft in JulyPeking WillowSalix matsudanahigh water, Central Valley4.27 gal/sq ft in JulyCoast RedwoodSequoia sempervirenshigh water, Central Valley4.27 gal/sq ft in JulyVine MapleAcer circinatumhigh water, Central Valley4.27 gal/sq ft in JulyHydrangeaHydrangea macrophylla & cvs.high water, Central Valley4.27 gal/sq ft in JulyBlueberriesVaccinium hybrids and cvs (CA native and non- native spp.)high water, Central Valley4.27 gal/sq ft in JulyShell GingerAlpinia zerumbethigh water, Central Valley4.27 gal/sq ft in July

Similar plants that need less water 16

Rated lower than red alder in the Central Valley. Worth a look for a new bed or a lawn replacement.

Citrus TreesCitrus spp.moderate water, Central Valley2.67 gal/sq ft in JulyJapanese MapleAcer palmatummoderate water, Central Valley2.67 gal/sq ft in JulyAvocado TreesPersea americanamoderate water, Central Valley2.67 gal/sq ft in JulyMagnolia TreesMagnolia grandiflora ssp. & cvs.moderate water, Central Valley2.67 gal/sq ft in JulyPalm TreesSyagrus romanzoffiana (Arecastrum romanzoffianum)moderate water, Central Valley2.67 gal/sq ft in JulyApple TreesMalus spp. (edible) e.g, 'Anna' (low chill variety for low desert)moderate water, Central Valley2.67 gal/sq ft in JulyPeach TreesPrunus spp. ediblemoderate water, Central Valley2.67 gal/sq ft in JulyPersimmon TreesDiospyros kakimoderate water, Central Valley2.67 gal/sq ft in JulyAmur MapleAcer ginnalamoderate water, Central Valley2.67 gal/sq ft in JulyFernleaf MapleAcer japonicummoderate water, Central Valley2.67 gal/sq ft in JulyBox ElderAcer negundomoderate water, Central Valley2.67 gal/sq ft in JulyNorway MapleAcer platanoidesmoderate water, Central Valley2.67 gal/sq ft in JulyRed MapleAcer rubrummoderate water, Central Valley2.67 gal/sq ft in JulyChinese MapleAcer truncatummoderate water, Central Valley2.67 gal/sq ft in JulyRed BuckeyeAesculus paviamoderate water, Central Valley2.67 gal/sq ft in JulyRed HorsechestnutAesculus x carneamoderate water, Central Valley2.67 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 red alder, 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 red alder in summer?

In July, established red alder in loam needs a deep watering about every 5 days in the Central Valley, about every 7 days on the south coast and about every 5 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 red alder need per day?

In July in the Central Valley, established red alder needs about 11 gallons a day under a 10 foot canopy and about 43 gallons a day under a 20 foot canopy. Give it in deep waterings spread days apart rather than a little every day, so the whole root zone gets wet.

Does watering for red alder change across California?

Yes. WUCOLS rates red alder separately for each of the six California climate zones: high water in the North-Central Coastal zone, high water in the Central Valley zone, high water in the South Coastal zone, high 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.

Is red alder native to California?

Yes. It grows along the coast from Point Reyes north to Crescent City, inland into the Shasta area, and historically south to the Santa Ynez Mountains. It is a tree of streams, marshes and moist forests.

Can red alder handle wet or salty soil?

Yes. It tolerates poor drainage, seasonal flooding and salty, brackish water, which makes it useful in bioswales and along runoff channels. It also fixes nitrogen.

Do red alder roots damage pavement?

Its root damage potential is rated high, so plant it well away from foundations, paving and pipes. A streamside or open low spot suits it best.

How cold can red alder handle?

Its stems can freeze at about 10 to 15 degrees, and trees have died near 0 to 5 degrees. Coastal winters rarely get that cold, but inland cold snaps can.

Does red alder cause allergies?

Its pollen is listed as an allergy hazard, which matters near homes with sensitive residents. Plant it at a distance from windows and outdoor seating.

More plant watering guides

Black CottonwoodCarolina PoplarOrnamental RhubarbWeeping WillowPeking WillowWillowSteviaDelphinium

Sources