You see, silly, black walnut trees, including branches, leaves, nuts, and, most importantly, roots, contain a substance called juglone, which sounds like a character from Jersey Shore and is just as dangerous to vegetables. Now, it's not deadly for all fruit and veggies, but let's just say don't try to grow tomatoes in a row garden within 50 feet of the drip line of the merciless and fiendish tree, that goes for potatoes, eggplant, peppers, and cole vegetables, too. The good news is that some tasty and fun plants WILL grow within sight of these harbingers of death, including melons and carrots, squash, corn, and beans, so you can still do the row thing right up next to Mount Doom, no problem. Guys like me are suckers for cherry tomatoes and hot peppers, so I just had to find a way around this dilemma.
And don't get me started on the baseball-sized nut pods that fall off these things, you can't even eat the nuts contained within. I opened one up once, only to get coated in a greenish substance that soaked into my skin and didn't fade for like two weeks, my hands were green, I shit you not, green. They're also delightfully invisible when mowing the lawn and produce a wonderfully relaxing sound when coming into contact with any kind of mower blade that will send you running for the telephone, clutching your chest. But you'll need to clear them off your grass if you don't want a huge brown spot on your lawn that will never ever go away, so approach with caution.
Like Minas Tirith (for all of you who don't know what Minas Tirith, it's ok, just go with it), my garden has ever existed within the shadow of the Black Gates, a shining beacon of hope in an ocean of the lost and the dark. The above-ground square-foot garden is the vanguard, our last defense against the armies of the night. But it takes vigilance, I'm out there all of the time making sure there are no leaves of the accursed in my bed, I've also plucked a soft maple tree or two from the soil, flown in on a helicopter from across the yard. But trust me, the effort you put into weeding an above-ground bed is nothing compared to the effort you'll put into weeding a row garden. I have plenty of friends that were driven into the ground and soured on gardening by their parents, forcing them to slave for half hours on end, weeding row gardens when they should have been at the gas station, playing Street Fighter II, or smoking cigarettes under the neighbor's porch, or in the woods, poking a dead raccoon with a stick. I won't lie to you and tell you that weeds don't love the nutritious and luxurious soil of a box garden, they do, but they are so much easier to pull out of loose, moist soil that's neither too wet nor too dry, and it's harder for them to get blown up into the bed in the first place, so you have far less of them, and since your garden is so low-maintenance, you'll be looking for any excuse to spend time with it.
Within reach of Mordor, there is still hope, even if you cannot see it. Enjoy your box garden.