This came up in another forum so I am posting it here.
My yard has a massive 70 foot tall Black Walnut tree. It is a small yard so everything grows near the tree or close to it. All fruit trees get mulched with Walnut leaves. Tomato beds get Black Walnut compost.
I’ve not noticed any negative effects on any of my fruits or vegetables.
My yard had a black walnut between the sidewalk and the street. One set of roots extended to one of the front gutters. No tomato or potato could live between sidewalk and street or near the gutter. Garlic, squash and other plants were severely stunted. Even thyme eventually succumbed, though parsley, chives, oregano, mint, sorrel and other herbs survived. Live BW roots is another matter compared to dead BW material. I did have BW leaves in mulch and they did not affect mulched plants much.
Black walnut…at least in my yard have got to be one of the fastest growing trees i’ve seen. I have 3 now all planted by squirrels and they have exploded in height in just a few short years. I leave them because of the shade they provide although i did prune some of the lower large branches off one of them. They also fruit pretty fast from seed…just a few years and you can have at least a handful of nuts.
Raspberries dont’ seem to care much because they grow right under one of them.
Black walnut is seriously allelopathic to many species including most fruit trees. Blue Grass is insensitive to juglone and grows symbiotically with walnut. Maples are highly sensitive. Juglone is produced heaviest by the roots. Leaves have relatively little but will affect sensitive species such as solanums (tomato, potato, eggplant, pepper).
Have you found Black Walnut to hurt your tomatoes/fruit trees? In your personal observation?
I have grown tomatoes for over a dozen years on this property. I have several mature fruit trees (15 years old or more) Cherry, Plum, Apple, Fig, Persimmon as well as Mulberry, Blueberry. And many new ones (loquat, pears, quince etc.). They all do decently well.
Oh, I also have several Japanese Maples not far from the Black Walnut. They are also doing very well.
Inconsistent results have been the bane of juglone allelopathy research. For every report of toxicity in a tested species, another report will find no effect. Researchers have pointed out a number of problems with initial assumptions and laboratory trials, which are summarized below: • Juglone, a highly toxic chemical, is not found in intact tissues of black walnut trees (Strugstad and Despotovski 2013). Instead, living tissues contain a nontoxic precursor called hydrojuglone, which is transformed in the soil to make juglone (Achatz and Rillig 2014). • Most hydrojuglone is contained in the roots and shells of walnuts (Figure 2). There is little in the leaves and virtually none in the wood (Lee and Campbell 1969). • Many researchers use artificial experimental methods to test for allelopathy. For instance, soilless media and laboratory extractions of juglone from walnut tissues do not occur in nature (Inderjit and Foy 2001). • Allelopathic responses are enhanced when potting media are used instead of soil. This is attributed to the increased permeability of the media compared to soil (Parepa and Bossdorf 2016). The lack of field test evidence to support laboratory results has spurred critics to insist that experimental testing include a functional soil system to more closely mimic what happens in nature. They note several conditions and activities that may account for the lack of positive field test results: • Juglone undergoes chemical, physical, and biological degradation in the soil (Inderjit 2001). • Organic matter and clay particles in soils can bind juglone, reducing its movement within the soil (Inderjit 2001). Figure 2. Walnut surrounded by husk. Photo courtesy of Monika Pickles. • Juglone does not persist in soils with high microbial activity (Jilani et al. 2008; von Kiparski et al. 2007).
And the conclusions by the authors:
Mulch well with arborist wood chips to retain soil moisture and to nourish beneficial soil life including mycorrhizae. • Enjoy your walnut trees! Not only are they robust landscape plants they provide food and habitat for wildlife. In areas with thousand-cankers disease, however, they should not be planted. • Use walnut wood chips for mulch if you have them. They will not harm plants and work just as well as those from any other woody species.
Have you verified you actually have a black walnut.?
Pecans, white walnuts, hickory…all have some juglone…but not nearly the same quantity/dosage.
Besides raspberries, sweet potatoes, tulips, daylilies, daffodils, oriental lilies, Lenten rose (helleborus), catmint, wormwood, golden rain tree, juniperus virginiana…………are some trees and plants I know will grow under a black walnut. The jury’s out on mountain laurel and deciduous azaleas…in other words I’m trying it and they look a little sick.
K8t, I have muscadines growing in and all the way through the crown of black walnut trees with no issues. I would still avoid planting a muscadine in any area where a tree’s roots will be in competition because it will reduce production of fruit.
Ramv, do things your own way. I have no interest in disagreeing. What I do have is 50 acres of black walnut trees growing and producing walnuts. I also grow about 350 tomato plants each year. If you guess that I don’t plant tomatoes in the walnuts, you are correct.
Does anyone know of nut-free cultivars of eastern black walnut? If they existed they would be a quick-growing shade tree. They have some problems - their compound leaves have sort of messy stems and the alleopathy. But good God, the rain of Freeman maple samaras was like snow in our neighborhood this year. So even they have their problems (e.g. poor branching structure).
I also have a friend who has a small orchard in his spacious front yard. At the corner stands a large BW. Trees within 40 ft of it are stunted. He basically gets all his fruit from past the 45 ft line. he should trench at 30 ft.
Maple helicopters are the worst…especially if you have open gutters.
MY mil needs a new tree (west side of house). She had a maple but it had dual trunks and split right down the middle. Too bad because it provided a ton of shade. I think i’m going to plant a seedling oak in its place. Red oak. Don’t see a lot of them as yard trees around here.
Hmmmm… I think a park near here was hit bad with that a few years back. Pretty soon we won’t have any hardwoods left! With elms, ash all toast… I do have some burr oak seedlings…they just seem a little slower growing then the reds.
“Oak wilt is always fatal to trees in the red oak group, which includes northern red oak, northern pin oak, and black oak. Trees that were infected with the oak wilt fungus this spring will begin rapidly dropping their leaves in July and August.”
I didnt’ realize it was fatal to the tree. I’ll have to check mine over (i have many).