WateringTimesWatering plan, $19
Juglans nigra, WUCOLS IV

How often to water eastern black walnut in California

In July in the Central Valley, established eastern black walnut in loam needs a deep watering about every 8 days: about 55 gallons each time under a 10 foot canopy, about 47 gallons a week. Eastern black walnut is a massive, fast-growing deciduous tree from central and eastern North America. It is grown for shade, fine timber and edible nuts in staining green husks. It sends down a very deep taproot. Its roots and leaves release juglone, which stunts some plants growing beneath it.

TreeRated for 3 of 6 zones

How often to water eastern black walnut, 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 eastern black walnut 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 to 6 inches down at the canopy edge of a young black walnut means it needs a deep soak
  • Leaflets yellowing and dropping early in late summer, over dry soil, can point to drought stress on a young tree
  • Small dark cankers that ooze and stain the bark, each with a pinhead hole, point to thousand cankers disease rather than thirst
  • Wilting over soil that stays waterlogged warrants a check for root rot, which can affect black walnut
  • Tomatoes, azaleas or blueberries wilting under the canopy may be reacting to juglone, not to dry soil

How to water it

  • Water a young tree over its root ball and well beyond it, since the taproot heads straight down
  • Apply water slowly so it soaks 18 inches or more, then let the upper several inches dry
  • Spread emitters across the outer canopy of an older tree and keep the trunk base dry
  • Plant in deep, rich, well drained soil in full sun, where the taproot can go down unchecked
  • Give deep soakings through dry summers so the tree avoids the stress that invites walnut twig beetles

Through the seasons

Water a new black walnut deeply through its first few summers so the taproot keeps heading down. Established trees are tough about heat and compacted soil, but deep summer soakings still matter, since stressed walnuts draw twig beetles. Nuts ripen in October inside yellow-green husks, and the tree stands bare through winter. Winter rain covers the cool months on the coast and in the Central Valley. WUCOLS rates it moderate water in the Central Valley, on the north-central coast and on the south coast. WUCOLS marks South Inland, the high desert and the low desert as not suited for it.

In pots

Black walnut grows a very deep taproot and transplants poorly, so a container is only a short stop for a seedling. Use a deep, narrow pot. Check the mix 2 inches down every few days in summer, and water until it drains through the bottom. Empty the saucer afterward. Plant the seedling out while it is still small, before the taproot has nowhere left to go. Through winter the leafless seedling needs only light, occasional water.

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

Eastern Black Walnut: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.370.40.78–––
Feb0.530.650.81–––
Mar0.871.091.15–––
Apr1.181.521.4–––
May1.462.081.61–––
Jun1.612.481.74–––
Jul1.612.671.98–––
Aug1.492.391.86–––
Sep1.241.81.49–––
Oct0.871.181.15–––
Nov0.470.560.84–––
Dec0.310.340.65–––
Year1217.1115.5–––

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 moderate water in the Central Valley, like eastern black walnut. Plants that drink alike can share one valve and one schedule.

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

Similar plants that need less water 16

Rated lower than eastern black walnut in the Central Valley. Worth a look for a new bed or a lawn replacement.

Olive TreesOlea europaea ssp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyFig TreesFicus carica ssp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyCrape MyrtleLagerstroemia spp., hybrids & cvs.low water, Central Valley1.07 gal/sq ft in JulyAloeAloe spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyPomegranate TreesPunica granatumlow water, Central Valley1.07 gal/sq ft in JulyEucalyptusEucalyptus polyanthemoslow water, Central Valley1.07 gal/sq ft in JulyPine TreesPinus canariensislow water, Central Valley1.07 gal/sq ft in JulyJunipersJuniperus spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyTexas Red OakQuercus buckleyilow water, Central Valley1.07 gal/sq ft in JulyPortuguese OakQuercus faginealow water, Central Valley1.07 gal/sq ft in JulySoapbark TreeQuillaja saponarialow water, Central Valley1.07 gal/sq ft in JulyNecklace TreeSophora affinislow water, Central Valley1.07 gal/sq ft in JulyBailey AcaciaAcacia baileyanalow water, Central Valley1.07 gal/sq ft in JulySilver WattleAcacia dealbatalow water, Central Valley1.07 gal/sq ft in JulyGreen WattleAcacia decurrenslow water, Central Valley1.07 gal/sq ft in JulySydney Golden WattleAcacia longifolialow 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 eastern black walnut, 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 eastern black walnut in summer?

In July, established eastern black walnut in loam needs a deep watering about every 8 days in the Central Valley and about every 11 days on the south coast. 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 eastern black walnut need per day?

In July in the Central Valley, established eastern black walnut needs about 6.8 gallons a day under a 10 foot canopy and about 27 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 eastern black walnut change across California?

Yes. WUCOLS rates eastern black walnut 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, not suited to this region 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.

What can I plant under a black walnut?

Avoid juglone-sensitive plants such as tomatoes, azaleas, peonies, apples and blueberries under the canopy. Choose tolerant plants instead. Keep their irrigation from soaking the walnut's trunk.

Can I transplant a black walnut?

Only while it is very small. Its deep taproot makes older trees hard to move. Plant seedlings where you want them to stay.

When will my black walnut produce nuts?

Some trees bear at about six years, but a substantial crop usually takes around 20 years. Nuts fall in October inside green husks that heavily stain hands and clothing.

What are the oozing spots on my walnut's branches?

Small dark cankers that ooze, each with a tiny hole, point to thousand cankers disease spread by the walnut twig beetle. Chemical controls are not recommended, so keep the tree free of drought stress. Have an arborist confirm the diagnosis.

Is black walnut harmful to dogs?

It is listed as a problem for dogs and horses. Keep pets from chewing fallen husks and nuts, and rake them up in fall.

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Sources