Can a garden survive SEVEN black walnut trees nextdoor?

August 4, 2026

This week, Mike unlocks the secrets of the dreaded black walnut for a gardener who has SEVEN of the tomato-killing trees growing next door

Courtesy of Wikipedia

Arnold in College Park Maryland, writes:

“I live next door to a person who has about six or seven black walnut trees. Some of the branches reach over my garden. What can I do to battle the juglone these trees produce? I try to quickly rake off most of the leaves. I heard the roots also affect the garden. Could black walnut leaves be guilty? And how far do the roots of black walnut affect the garden?

I had also been using citrus fruits in the garden, but stopped recently. Could that have caused my pH to rise to 7.4? We normally can 15 quarts of beans, but last year we only had enough for one meal.

Any suggestions would be greatly appreciated. Oh, and I wish you could come back to the College Park area again. I really enjoyed your presentations.

A; Thanks Arnold—I, too, miss those days. I was the (mostly remote) garden reporter for the top rated news station WTOP in DC for 20 years (concurrent with You Bet Your Garden on NPR), and made dozens of appearances (maybe over a hundred) in the Greater DC area. I have fond memories of College Park, where a close friend I stayed with when speaking in the area lived near the Zoo, which is part of the Smithsonian and therefore free (a great use for Tax Dollars, say I.)

And you made me remember (and miss) the annual Flower Mart weekend at the National Cathedral (a destination in itself; try and find the Darth Vader “gargoyle” up on the roof!). Produced by the All-Hallows Guild and benefiting the Cathedral’s wonderful gardens, I especially remember the carousel.

To quote the Flower Mart page:

“The All Hallows Guild’s antique carousel is a favorite of the young and young at heart. It dates from around 1890, and is one of only two surviving carousels manufactured by the U.S. Merry-Go-Round Corporation. The carousel was purchased by the Guild in 1963 and we continue to restore and refurbish this historic treasure.”

Anyway, the event is held the first weekend in May and is worth the trip. (Visit the Zoo next.) End of travelogue (you KNOW I can’t help myself!), and back to a question that is well worth the stall:

You have two seemingly unrelated issues. Let’s talk about juglone first.

A naturally occurring compound that black walnut trees use to suppress the growth of other plants in their area, limiting competition for nutrients and water, juglone inhibits the growth of some—but not all plants—in the area of its dripline. Unfortunately, tomatoes are the most negatively affected plant. AND the roots of a mature Black walnut can easily reach 150 feet. (Sorry, I’m only the messenger.)

In other words, it is impossible to grow tomatoes anywhere near a black walnut (much less SEVEN (!)), as most sources agree that the juglone content is most concentrated in the roots. (But juglone is also in every part of the tree: lumber, leaves, nuts…Oh and before I forget: the trees would not raise your soil pH. In fact black walnut trees grow best in a slightly acidic soil, say 6.5 on the pH scale—just like tomatoes.

We’ll get back to your baffling rise in pH in a moment. For now, let’s concentrate on the army of black walnuts growing nearby. Unless you’re trying to grow a garden nearby, these are excellent trees with valuable wood, shelter for birds and food for wildlife via the green grenade softball-sized encased nuts they drop in the early fall. (They come down HARD; never park under a black walnut tree!)

And with that many trees nearby, you MUST be tormented by Evil Squirrels burying the nuts on your property. At my house, we have to rip out LOTS of walnut sprouts in the Spring—and I only have to deal with one tree across the road. (That road and my raised beds seem to protect my tomatoes from their roots, so other than Evil Squirrel mischief and my thinking that someone in the woods is throwing things at me every Fall, it’s not a problem.)

You have the right to prune off or legally demand that your neighbors remove any branch that crosses the property line. It’s the law. At the very least, it might let in more sun for you to grow some of the many native plants that are not only immune, but benefit from growing near black walnuts.

The easiest and most inexpensive solution is to stop trying to grow vulnerable plants there. Ideally you would move your garden to another spot that’s unaffected (like the front of the house as opposed to the back or vice versa).

But I know your neighborhood well and you might not have another in-ground option. To take some blame away from the trees, among the food plants unaffected by juglone are green beans (so the trees are not responsible for your poor harvest last year), and squash. It’s likely your unusually high pH that’s to blame.

That said, the easy and inexpensive answer here—especially if you can’t move the garden next season--is to grow in containers atop the same spot; use the biggest ones you can find; and put them up on bricks to ensure good drainage and avoid their roots touching the soil.

There’s a good variety of {quote} ‘raised beds on legs’ that would be perfect here. Fill them with fresh, clean sifted topsoil, REAL compost (homegrown compost must consist of at least 75% shredded leaves [try and avoid the black walnut leaves], and don’t use whole leaves; they MUST be shredded; and mix in about 20 percent perlite to ensure good drainage).

Although shredded fall leaves will become compost on their own, some green material can be MIXED in. The best addition is used coffee grounds—yes, they qualify as ‘green’ because of their Nitrogen content. Shredded leaves and spent coffee grounds make perfect compost. UNCOOKED kitchen scraps can be used, but nothing that’s been cooked; and certainly, no citrus of any kind. And no grass clippings; leave them on the lawn to feed the turf and you might not need to otherwise feed it.

Then you can grow whatever you like for a small investment (the raised bed frames and joiners) that will nicely amortize over time. Do not use ANY of your current soil. It has a LOT of things wrong with it.

It also sounds like you might be growing in flat ground. If you follow this new version of the show or remember me from WTOP, NPR, and/or as Editor-in-chief of ORGANIC GARDENING, you know what I think of flat earth gardening.

If you want to try building raised beds atop the original soil, placing thick heavy cardboard on the ground before filling the beds will greatly reduce the chance of any roots getting in. Then have a trench dug and rhizome barrier installed on your side of the property line to prevent future incursions. Here’s what Biology Insights has to say about those nasty roots:

“The depth and spread of walnut tree roots are influenced by soil type, moisture availability, and the tree’s age. In fertile, moist soil, a young walnut’s taproot can penetrate 24 to 30 inches deep, while in sandier, drier conditions, it may reach up to 4 feet. Mature trees can have main roots reaching 20 to 23 feet deep, though most of their root mass usually remains within the top 3 to 7 feet of soil.”

So: either move the garden, use containers or raised beds on legs or build raised beds on top of your existing soil beginning with heavy cardboard overtop of the soil to prevent the walnut roots from getting in.

Now for the worst problem: Your soil pH. Soils in the greater DC area (and most of the mid-Atlantic) tends towards acidic, so you must have added something serious to make it so alkaline. Search every soil amendment you have added for their effect on soil pH. (Wood ash is a common culprit.) An excessively alkaline pH is extremely rare in your area. And that high pH inhibits the uptake of many macro and micronutrients that summer garden crops need to survive.

There are other explanations, but your high soil pH is not explained by any of them. Don’t know what you did, but don’t do it again.

And finally, your use of “citrus in the garden” mystifies me. What did you hope to achieve? Full, cut citrus halves are used on stands to attract and feed certain birds; and citrus rinds are an old school way to attract slugs, which you would then dispose of citrus and all in the morning. Are you tossing lots of kitchen waste on top of your garden? It’s no help to the garden, but it is a great way to attract mice, rats and raccoons (which, yes, you have in abundance, but they work at night).

A pH that high would require some form of natural sulfur to correct.

From the University of Minnesota Extension:

Just as you would add lime to acidic soil to raise the pH, you can add sulfur to basic soil to lower it. This is one of the least labor-intensive ways to reduce the pH of your soil, though it takes time. Often, annual or biannual repeat applications are necessary to actually maintain a lower pH. The basic concept is: you add sulfur to your soil, ideally in the fall, and the microbes in your soil will break it down into sulfuric acid. This process takes time, and by applying sulfur in the fall, you can start to reduce your pH before the next growing season.

The Nutrient Management Guide for Commercial Growers has a full list of sulfur products available to fruit and vegetable growers. Organic growers’ options include elemental sulfur, calcium sulfate, potassium sulfate, and langbeinite.

See the ‘high pH section of their website for recommended amounts.

And good luck—you have some work ahead, but you CAN fix this.