Majestic mature trees are one of the delights of the established neighborhood in which I live. Maples, oaks, conifers, and elms line the streets. In my own yard stands an ailing Siberian Elm that is at least a hundred years old. It will most likely be standing long after the current residents of the neighborhood are gone. No one wants it cut down as long as the old girl still shows signs of life. I think of my self as a "tree hugger" who feels trees older than I am should be able to live out their natural lives. I do not mind raking leaves or trimming branches because the beauty of mature trees adds elegance to my neighborhood that cannot be duplicated in even the most exclusive of new home developments. I even live in an area that participates in the "Tree City USA Community" program that is sponsored by the National Arbor Day Foundation, U.S. Forest Service and others. It is because I have such appreciation for trees that my current search for a chain saw is so disturbing.
Towering over my back yard is a mature black walnut tree which dwarfs the nearby utility pole. I have yet to assess exactly how tall this tree is as its branches extend well into the two properties adjoining mine. Gracing my front yard is another, less mature black walnut tree. It merely towers over my house. It is these trees that I seek to destroy. I don't want to merely cut them down; I want to remove any and all of the root systems that may be located in my yard. Why you ask am I obsessed with destroying these two towering beauties? Because black walnut trees are the evilest of all plant life to an avid gardener. I have not come to this conclusion lightly, but after gardening around black walnut trees for six years, I know it to be true. Black Walnuts (Juglans Nigra L.) range in height from 70-150 feet and a diameter of 2-4 feet. See "Black Walnut" (http://ostermiller.org/tree/blackwalnut.html). These trees are toxic to a large number of ornamental annuals and perennials, trees and shrubs. Along with its cousin, the butternut (Juglans Cinerea L.), black walnuts' emit a chemical compound called juglone which causes yellowing, wilting and eventual death to plants sensitive to the compound. Juglone occurs naturally in all parts of the black walnut but the largest concentrations are found in the walnut buds, nut hulls and root system. See "Black Walnut Toxicity" (www.wvu.edu/~agexten/hortcult/fruits/blkwalnt.htm).
A zone of toxicity exists around black walnut trees due to the emission of juglone from the root system and to a lesser extent from the leaves and twigs. The zone is 50 to 60 feet from the trunk of a mature tree. See "Walnut Toxicity" Home Grown MSU Extension-Livingston County. Take a 100 foot ball of twine, tie it around the base of the tree trunk, and measure out 50-60 feet in a circle completely around the tree. If the branches of the black walnut extend past this circle, extend your circle to include those areas under the tree branch. This is your zone of toxicity and plants which are sensitive to juglone will not thrive and will most likely die if planted in this area. The root system of the black walnut tree causes most of the damage but the nuts, leaves and twigs from the tree will also poison sensitive plants.
My current homestead is not my first experience with a black walnut tree. My last home's backyard was graced with a black walnut that by its' size must have been close to one hundred years old. It was there I learned the joy of being pelted by green shell husks as hard as, but larger, than golf balls. I learned the pounding on the roof was not a hail storm but merely the nuts falling from their branches. Black walnuts are covered by a hard, thick, green husk which has an unpleasant odor and stains anything it comes in contact with. A favorite of squirrels, these husks are ready for harvest in August. Immature husks can be found, or felt, as early as late June or July.
I attempted to adapt and tried to harvest the nuts which are reputed to be excellent in desserts. First you need to collect the husks which smell, stain and are impossible to break. Some books recommend driving a car over them. Then you get to the nut shell. It also stains both your hands and your clothing. If it is not infested with insects, the nut must be cured and watched for mold. Then you get to try and break its' shell. I was not successful in harvesting black walnuts.
I also discovered you use the leaves of a black walnut tree as mulch at your own risk. Prior to learning of the existence of juglone, I shredded the fallen black walnut leaves and utilized them as both mulch and an ingredient in a compost "soup". I was starting a garden in the front yard from scratch in rocky soil and could not afford a truckload of topsoil. I mixed leaves that had sat in the yard for months with ground organic matter from the kitchen and rainwater. I used this mixture to fertilize perennials I had purchased at a local nursery for a quarter apiece. The plants were immature, but were supposed to be fast growing, self-sowing perennials suitable for my climate. My garden stagnated. I repeatedly checked the sun exposure, moisture, and other gardening factors. I finally attributed the lack of growth in my garden to the immaturity of the plants and waited for the next growing season.
Meanwhile I found out about juglone. I removed all of my organic much, and replaced it with bagged topsoil and commercial mulch. I stopped composting any of the leaves from my yard for fear of contamination from the black walnut leaves. The next year my front yard garden bloomed and thrived. The back yard was home to a black walnut tree and a smattering of grass. Only Kentucky bluegrass thrives under black walnut trees but I had not put down new seed yet.
Researchers claim black walnut leaves can be composted because" the toxin breaks down when exposed to air, water and bacteria. The toxic effect can be degraded in two to four weeks." "Black Walnut Toxicity to Plants, Humans and Horses HYG-1148-93" Ohio State University Extension Fact Sheet. This same research claims mulch from the bark is safe after six months. I disagree since the compost I used had been exposed to the elements for a time period exceeding four weeks. As is noted in "Walnut and It's Toxicity Explored" Cornell Cooperative Extension/Yates County by Tom Rood, the safety of black walnut byproducts in compost or mulch is debated. Unless you have the technical tools to chemically test for juglone in your compost or mulch, I think you use composted black walnut leaves or mulch at your own risk, or rather your garden's risk.
I moved to my new home with dreams of rhododendrons, hydrangeas, roses and columbine all of which are juglone sensitive plants that I could not grow in my old garden. The black walnut tree at my old house had a trunk diameter of at least three feet and only the Siberian Elm in my new front yard exceeded two feet. Roses grew on the side of the house so I grew excited about all the new gardening possibilities I had before me. Come fall a large green husk fell on my head in the back yard. I laughed, realizing my escape from the evil black walnut curse had not been complete. This black walnut tree is located in the rear of my yard surrounded by mulberry trees which are compatible with black walnuts. The area is deep shade even on the sunniest days so I planted hosta plants which are juglone tolerant and I had intended to do anyways. I have a sunny area near my rear door so luckily my herbs do not seem to be affected whatsoever by juglone. I had to give up on blueberries and tomatoes but lettuce and carrots grow just fine. I still planned for my flowering shrubs and perennial assortment for the front yard and even started planning where I could put a blueberry bush. I was in denial.
A neighbor told me he thought the tree next to the Siberian elm was a black walnut tree. He told me husks fell on his drive all fall. I couldn't see the tell tale green husks that identify a black walnut so I assumed the husks had been brought by squirrels from the tree in the rear of the lot. I spent my time regrading the front area near the house and redefining and enlarging the garden area. I spent large amounts of time tearing out the overgrown ivy and planning my garden space. I intended to buy mature plants to give the entry area a finished look but my budget and the weather required me to wait another planting season.
Come spring I located all the tulips that had been scattered around the front garden (tulips are said to be juglone sensitive) and looked forward to planting. It was not until my first purchase, a Cinquefoil, suddenly wilted and died that I suspected my neighbor was correct. At first I still could not locate any walnuts. I took a branch sampling and compared it to the tree in the back yard. They were suspiciously similar. I still did not want to believe but I did stop investing in mature shrubs. Over the summer I tried whatever plant was on sale. Some lived, some died. In August, a pair of binoculars confirmed what I had been trying not to see, the dreaded green husks hanging from the tree in my front yard. This house not only had one black walnut tree, it had two. I was in gardening hell.
Time has passed and I have researched plants that are not sensitive to juglone. None of the plants I had dreamed of are on the list and most confusing is trying to choose shrubs which are not susceptible to juglone. Yews are out, barberry in. I am waiting to see if my daffodils will bloom. Some are juglone sensitive. The bunch that was planted near the tree of death formed buds which were then stunted and did not bloom. Some of the fifty daffodils I planted bloomed; others formed no buds at all. I am waiting until spring. Maybe they were immature bulbs.
I have an area that is sheltered from both trees and their roots and it is there both my climbing roses and traditional rose bush thrive. It is a self contained bed between the drive and the house and is already at capacity. I am thankful for this small area and I keep a watch for any part of a black walnut tree which drifts near it and immediately remove any suspicious leaf or twig not to mention walnut. The landscape plan for the rest of the yard is limited to those plants not sensitive to juglone. But don't think I have totally given up on removing these trees from my life. I know the black walnuts are too large for me to remove with a chain saw but for a price you can hire tree services to do that kind of thing. Even if I had them removed, the juglone stays in the remaining roots for 1-5 years. I am willing to dig those out also but the task may be larger than I think. The toxicity zone is 50-60 feet in all directions. Today I can still dream of chain saws, and tree removal services, tomorrow someone may develop a poison that will destroy the entire tree, roots and all, in less than five years. Then I can plant my azaleas.