What plants are sensitive to the juglone produced by black walnuts?

FAQ
Question: 

What plants are sensitive to the juglone produced by black walnuts?

Answer: 

Juglone is a chemical that inhibits the growth of certain plant species.  When plants produce a chemical that prevents the growth of other plants, it is called allelopathy.  Black Walnut is a common woodland and landscape tree in the Midwest that produces juglone which causes an allelopathic response (inhibition of growth) in other plants.

Walnut fruit
Juglone is produced by all parts of Black Walnut (leaves, stems, fruit, etc.), making it a highly effective competitor for space in the landscape. Photo courtesy of Cindy Haynes. 

Not all plants are sensitive to juglone. Members of the tomato family (tomato, potato, eggplant, pepper) are highly sensitive to juglone.  Some shrubs like lilac, hydrangea, rhododendron, viburnum, and yew are also considered somewhat sensitive to juglone.  There are many other plants, however, that are not impacted by juglone.  Shade loving perennials like bugleweed and bleeding heart can coexist nicely underneath walnuts without any injury.  It is also important to note that many turfgrass species are tolerant of juglone.  They, like many other sun-loving plants, are more likely to perform poorly because of the shade of the walnut tree rather than the juglone.

The degree of symptoms varies with species.  Tomatoes are highly sensitive so they often yellow, grow poorly or look stunted, and eventually die when grown near walnuts.  Plants that are not as sensitive may yellow slightly or grow more slowly, but are rarely killed. And plants that are tolerant to juglone grow well with no signs or symptoms of injury.

A list of some of the sensitive and tolerant species to juglone are listed below.  It is important to note that there are no definitive lists and very few official studies on the impact of juglone on different plant species.  The plants listed below have been observed to grow well or not grow well when near black walnuts in a landscape or woodland setting.

Sensitive to Juglone

 

Tolerant to Juglone

Trees

Alder

Alnus glutinosa

 

Buckeye

Aesculus species

Apple/Crabapple

Malus species

 

Birch (some)

Betula species

White Birch

Betula papyrifera

 

Catalpa

Catalpa species

Linden

Tilia americana

 

Dogwood

Cornus species

Hackberry

Celtis species

 

Hawthorn

Crateagus species

Larch

Larix

 

Hornbeam

Carpinus caroliniana

Magnolia

Magnolia x soulangiana

 

Honey-locust

Gleditsia triacanthos

Silver Maple

Acer saccharinum

 

Maple (most)

Acer species

Norway Spruce

Picea abies

 

Mulberry

Morus species

Pine (most)

Pinus species

 

Redbud

Cercis canadensis

 

 

 

Sycamore

Platanus occidentalis

 

 

 

Oak (most)

Quercus species

 

 

 

Willow (most)

Salix species

Sensitive to Juglone

 

Tolerant to Juglone

Shrubs

Azalea/Rhododendron

Rhododendron species

 

Arborvitae

Thuja species

Chokeberry

Aronia arbutifolia

 

Barberry

Berberis species

Cotoneaster

Cotoneaster species

 

Beauty bush

Kolkwitzia amabilis

Hydrangea

Hydrangea species

 

Daphne

Daphne species

Lilac

Syringa species

 

Dogwood

Cornus species

Viburnum (some)

Viburnum species

 

Elderberry

Sambucus species

Yew

Taxus species

 

Fringe tree

Chionanthus virginicus

 

 

 

Forsythia

Rosythia

 

 

 

Juniper

Juniperus species

 

 

 

Mockorange

Philadelphus species

 

 

 

Rose of Sharon

Hibiscus syricacus

 

 

 

Serviceberry

Amelanchier species

 

 

 

Sumac

Rhus species

Sensitive to Juglone

 

Tolerant to Juglone

Annuals, Perennials and Bulbs

Autumn crocus

Colchicum species

 

Aster

Symphortrichum species

Columbine

Aquilegia species

 

Astilbe

Astilbe species

Daffodil (some)

Narcissus species

 

Begonia (most)

Begonia species

Flowering Tobacco

Nicotiana species

 

Bugleweed

Ajuga species

Lily

Lilium species

 

Bleeding heart

Lamprocapnos spectabilis

Peony (some)

Peaonia species

 

Cranesbill

Geranium species

Petunia

Petunia species

 

Daylily

Hemerocallis species

 

 

 

Ferns (many)

various genera

 

 

 

Hyacinth

Hyacinthus

 

 

 

Iris (many)

Iris species

 

 

 

Phlox

Phlox species

 

 

 

Stonecrop

Sedum species

 

 

 

Tulip (some)

Tulipa species

Sensitive to Juglone

 

Tolerant to Juglone

Fruits

Apple

Malus domestica

 

Black Raspberry

Rubus occidentalus

Blackberry

Rubus species

 

Cherry

Prunus avium

Blueberry

Vaccinium speices

 

Peach

Prunus persica

Grape

Vitus species

 

Plum

Prunus domestica

Pear

Pyrus species

 

 

 

Sensitive to Juglone

 

Tolerant to Juglone

Vegetables

Asparagus

Asparagus officinalis

 

Beans

Phaseolus species

Cabbage

Brassica oleracea

 

Beets

Beta vulgaris

Cucumber

Cucumis sativus

 

Carrots

Daucus carota

Eggplant

Solanum melongena

 

Corn

Zea mays

Pepper

Capsicum annuum

 

Melons

Citrullus species

Potato

Solanum tuberosum

 

Onions

Allium cepa

Rhubarb

Rheum rhabarbarum

 

Squash

Curcurbita species

Tomato

Lycopersican esculentum