[permaculture] Black Walnut Guild
robscott at freeshell.org
robscott at freeshell.org
Tue Feb 15 16:02:25 EST 2005
In response to the disparaging comments about Black Walnut, I'm posting my
research on Black Walnut ecology and companion planting. A list of
productive species for Black Walnut understory appears at the bottom.
Urbana Permaculture Project
Black Walnuts (Juglans nigra) and Hackberry (Celtis occidentalis) occur
together naturally, both are reported to be allelopathic, for separate but
overlapping sets of plants. In warmer climates, the closely related
Sugarberry (Celtis laevigata) would be a more fruitful associate.
Why is Black Walnut toxic?
Black Walnuts produce a toxin called "juglone" in all parts of the tree.
It is an antirespiratory compound with a phenolic ring. It probably
evolved to deter insect pests, not plants or humans. Fishermen have used
ground up walnut hulls to attract fish to the surface of the water; the
juglone slows fish respiration and the fish come to the surface to
breathe. Juglone in leaf litter degrades in about 2 days, so raked up leaf
mulch is not toxic. Walnut tree roots constantly release juglone, and this
is why nearby plants often die.
What companion plants help Black Walnut grow?
Control experiments in Illinois found that Autumn Olive (Elaeagnus sp.)
work better as a symbiont for promoting Black Walnut growth than Black
Locust (Robinia pseudoacacia). Both fix nitrogen, but the Autumn Olive
doesn't compete with the Black Walnut as much and seems to reduce deer
browse. The net effect of Black Locust was to set back Black Walnut by
shading. Degraded sites will yield different results as Black Locust
better restores depleted soils.
What naturally grows under Black Walnut?
Redbud (Cercis canadensis), Pawpaw (Asimina triloba), and Spicebush
(Calycanthus occidentalis) grow as understory shrubs under Black Walnut
naturally in Central Illinois. Ground level wildflowers are no less
abundant under Black Walnuts than in other natural forest communities.
Does Black Walnut create a lot of shade?
Black Walnuts let through a lot of sunlight. Shade is "dappled" even after
leaves have fully emerged. Bud break in Black Walnut occurs in late
spring, allowing sun penetration to the forest floor for a few months
before leafing out. A rust fungus commonly causes anthracnose in Black
Walnut leading to early leaf-drop and dormancy in the fall, adding another
month of full sun penetration. Understory shrubs have been shown to reduce
anthracnose infection by breaking the ground-to-leaf cycle.
What productive plants can grow under Black Walnut?
(in no particular order)
American Black Currant - Ribes americanum
European Currant - Ribes nigra, Ribes rubrum, Ribes alba
Missouri Gooseberry - Ribes missouriensis
American Elderberry - Sambucus canadensis
Black Raspberry - Rubus ideaus
Siberian Pea Shrub - Caragana arboescens
Mulberries - Morus nigra, Morus alba
Alpine Strawberries - Fragaria vesca
Goldenseal - Hydrastis canadensis
Wild Ginger - Asarum canadense
Pawpaw - Asimina triloba
Redbud - Cercis canadensis - legume
Bamboo - Phyllostachys spp.
"Rose of Sharon" Hibiscus - Hibiscus Syriacus
Lamb's Quarters - Chenopodium alba
Catnip - Nepata cataria
Daylily - Hemerocallis sp
Sunchokes - Helianthus tuberosa
This is a good way to control the spread of sunchokes, and the tubers are
of fine size and quality even when shade grown. Dandelions, Violets and
Creeping Charlie have also grown naturally in Illinois Black Walnut
Guilds. Toby Hemenway mentions Woldberry (Lycium spp) in Gaia's Garden for
growing near Walnut, but it doesn't grow well in Illinois.
More information about the permaculture