Planting Near A Walnut Tree

Walnut Tree (Juglans spp.)

When selecting plant material for a home garden it is important to first take inventory of the trees on your property and neighbouring properties. Trees like walnut can present a real challenge for gardeners. Not only do the plants you select have to deal with shade and strong competition for water and nutrients, (as with planting near any large tree), they additionally have to contend with a toxic substance called juglone. Juglone is a chemical given off by the roots, nut hulls and leaves of walnut trees. It acts as a growth inhibitor, which in essence is nature’s way of suppressing the competition in order to ensure its survival. Some plants however are sensitive to the juglone and will die if grown near nearby.

The area directly under the walnut canopy has the highest concentration of juglone but because of the expansive root system of walnut trees, juglone sensitive plants grown within 20 to 30 meters can be adversely affected.

Symptoms

Symptoms of juglone toxicity appear as wilting, yellowing leaves, stunted or slow growth and eventually death. Certain plants are more sensitive to juglone than others. Plants highly sensitive to juglone may die within a few months.

Identifying Black Walnut Trees

The Leaves:

  • The leaves are oddly pinnate containing 5-25 leaflets.
  • These leaflets have serrated edges.
  • The leaves are arranged alternately on the branches.
  • The leaves, when crushed smell like spiced citrus.

The Bark and Branches:

  • The bark is furrowed and dark brown to deep-gray in colour.
  • The bark has rounded ridges and deep crevices running vertically up and down the trunk.
  • There are leaf scars, (that are in the shape of a shamrock), along the twigs, where the leaves pulled away from the branches.
  • The shoots and twigs have chambered pith.

The fruit:

  • Look for round, green fruit casings on the ground or in the tree about the size of a tennis ball.

Flower:

  • Yellow-green catkins. The female flowers have pink or reddish pistils. 

Over all Shape and Form:

  • Walnut trees develop broad canopies reaching 18 m width and 30 m in height.
  • They have a strong central leader with dense, heavy branches.

Note: English walnut trees look almost the same but they are typically grown in orchards. The butternut walnut is not of concern here as it does not produce enough juglone to be a problem.

Plants to Avoid

 (These plants are sensitive to the effects of juglone and will not perform well near a walnut tree). The names in bold are particularly sensitive.

  • Apple
  • Asparagus
  • Aster
  • Autumn Crocus
  • Azaleas
  • Blackberry
  • Black Locust
  • Black Oak
  • Blueberry
  • Birch
  • Cabbage
  • Columbine
  • Cotoneaster
  • Crabapple Spp.
  • Egg Plant
  • European Alder
  • Hydrangea
  • Larch
  • Lilac
  • Lily (Asian)
  • Linden
  • Magnolia (saucer)
  • Mugo Pine
  • Northern Red Oak
  • Norway Spruce
  • Peony
  • Peppers
  • Petunia
  • Potentilla
  • Potato
  • Privet
  • Red Choke Cherry
  • Red Pine
  • Rhododendron
  • Rhubarb
  • Silver Maple
  • Tomato
  • Viburnum (some species)
  • White Birch
  • White pine
  • Yew

Plants to Try

(These plants are more juglone tolerant and can usually be safely planted near a walnut tree). For a more extensive list check Morton Arboretum

  • Arborvitae
  • Astilbe
  • Ajuga
  • American Beech
  • American Chestnut
  • American Elm
  • American Hornbeam
  • Beauty Bush
  • Bleeding heart
  • Box Alder
  • Bearded iris
  • Bittersweet
  • Black-eyed Susan
  • Bugleweed
  • Clematis
  • Coralbells
  • Cranesbill
  • Current
  • Daffodil
  • Daylily
  • Elderberry
  • Flowering Dogwood
  • Forsythia
  • Fringe Tree
  • Hawthorn
  • Hellebore
  • Hickory
  • Hollyhock
  • Honey-locust
  • Honeysuckle
  • Hosta
  • Japanese maple
  • Juniper
  • Korean Spice Viburnum
  • Lamb’s Ears
  • Lily-of-the-valley
  • Lobelia
  • Lungwort
  • Mock Orange
  • Ninebark
  • Pagoda Dogwood
  • Paw Paw
  • Persimmon
  • Redbud
  • Red Maple
  • Rose of Sharon
  • Scarlet Oak
  • Sedum Spp.
  • Service Berry
  • Slipper Elm
  • Snow Drops
  • Solomon’s Seal
  • Southern Catalpa
  • Spiderwort
  • Staghorn Sumac
  • Sugar Maple
  • Summer Phlox
  • Tulips
  • Tulip Tree
  • Violets
  • Virginia Creeper
  • Wild Plum
  • Willow
  • Winged Euonymus 
  • Wisteria
  • White Oak
  • Witch Hazel
  • Woodland Phlox
  • Yarrow
  • Yellow Birch
  • Yellow Buckeye
  • Yucca

For those who wish to grow vegetables near a walnut tree try constructing raised beds and line them well to keep out walnut roots. Container gardening is also an excellent option.

All rights reserved

Terms of use: photos and content may be used for non-profit use and education with proper attribution and link back to page found.

For photos: Kimberley Pacholko Planting Near A Walnut Tree – Horticulture For Home Gardeners

For content: Kimberley Pacholko 2021, Ornamental Garden Specialist, Planting Near A Walnut Tree – Horticulture For Home Gardeners

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s