The tree bordering the vegetable garden will likely have roots growing into the space. If so, it may create problems. The one 30 ft away, most likely has roots growing into the space, and it too may create problems. I doubt the other one will be an issue, but you'll need to have a little understanding of the chemical that causes the problem.

If you have the ability, removing the roots is the best option. Juglone isn't water soluble, so it doesn't travel far from the source. It also breaks down relatively fast in the presence of oxygen and microbial activity. However, if roots are left in the ground, they will exude the chemical until they have broken down completely. So, just killing the trees won't work. You have to physically remove the roots, then work air, nitrogen, and organic matter into the soil to create an active soil biome which will help decompose both the juglone, and any root mass that was left behind. Ideally, you would do this a few years before you plant, but there are juglone resistant crops which can be grown in the areas heavy with roots and rootlets.

As for the tree far enough from the space... just don't work the leaves, twigs, nuts, hulls, bark, etc... into the soil and you should be fine. As the plant material is breaking down, the chemical is released. Once juglone is exposed to air and microbial activity, it only lasts a few weeks before it too breaks down, but it's incremental. It takes time for each part of the plant material to decompose. So, you can compost leaves, but working them into the soil before you plant may not be the best choice.

First, pause a minute, the trees may be of considerable value.

• ''...a mature stand of black walnut trees can bring about $100,000 per acre in timber value alone. ..''

Now, think about your gardening. Are you really sure you have a problem?

Juglans nigra - Plant Finder - Black walnut roots produce chemicals called juglones which are very toxic to certain other plants such as azaleas, rhododendrons, blueberries, peonies and solanaceous crops (tomatoes, peppers, potatoes). Most of the toxicity is limited to within the drip line of the tree, but the area of toxicity typically increases outward as the tree matures.

I have a large black walnut tree in the front yard, clay soil. I did experiment with some veggies in a flower bed and the veggies grew but stayed small (8 years later i still have some garlic coming up). The current tenants of the bed are various perennial flowers and they thrive without any help, not even water. Those (Black Eye Susan, bronze fennel, echinacea, irises and asian lily) really are fully resistant. There is a range of resistance and IMHO none of the veggies I tried is fully so, although I tried them early before the soil became better (see comment below). They were chard, allium and cucurbita. carrots and beans are also thought to have some resistance.

Near the orchard (same clay) I have two black walnut trees, about 20 and 25 ft from the edge. I planted peaches, persimmon, pawpaw and mulberry (all resistant) in the nearest spots. I also dug a trench at the border, and I girdled the trees. The girdled trees have fully recovered, but so far I got no problems. BW roots are fairly easy to identify, being black with yellow wood, and I have not seen live BW roots past the trench, although I stopped looking 5 years ago.

A friend has a front yard orchard in very sandy soil, with a meager lawn. All trees within a radius from the BW suffer, and its striking to see that tree health improves as you get farther. That BW (which is very large) has a poisoning range of order 40 ft, but I wonder if the poor soil plays a role.

In highly biological soils juglone does not persist, so maybe my flowerbed (20 ft from a large BW) got better by trapping leaves in fall and letting nature doing its thing. Same for the orchard, which got a lot of wood chips and is now a thriving prairie. I would not be worried about dead roots. Cover crops, for example, will indirectly degrade juglone. In a petri dish with juglone and the widespread pseudomonas bacteria, the juglone disappears in minutes. Numerous fungi are thought to also degrade juglone. You may start by renting a trencher to kill all roots past the trench and down to the trench depth, keeping the most sensitive plants (tomatoes) as far away as possible, and proceeding with tree cutting once problems show up.

You've got plenty of info here about the effects of juglone, but let me also highlight Albert's first point. If you decide to remove any Black Walnut tree(s), look into the potential value. Black Walnut is a sought after type of wood and you may very well offset the removal costs or probably walk away with a profit.

I agree with Albert that your trees MIGHT have some value, and certainly you should check into it. But you should also be prepared that all you might have is firewood.

Because of the cost of their blades, and the chance that at some time someone may have attached a sign such as a "No Trespassing" sign or "Yard Sale" (or a fence), many sawmills will not take a chance on a tree that has been in a yard or along a boundary.

I used to work for a hardwood lumber company and every time a storm would bring trees down, we were inundated with phone calls from people who had lost a tree and whose neighbors told them that they really had a goldmine. Sadly, we had to give them the bad news--firewood value only.

"...I want to start a vegetable + fruit/nut tree farm..."

And you want to remove the Black Walnuts? I would think the nut value would surpass veggie value. Were you going to put all this in one acre? Grow the fruit trees between the walnuts and the veggies and put the taters, maters and peppers at the furthest point from the walnuts. Though not as strong at Black Walnut, many nut trees contain some level of juglone.

tj