Describe the "small mound next to the girdled area, please. Are you describing callus tissue? Air layers don't get "irritated or distressed" when rubbed, but 'checking' them can result in unnecessary breakage of roots. If you use clear wrap to hold your rooting medium in place, then wrap that with aluminum foil to keep the sun from over-heating the medium or impacting root development, there should be no reason to peek. The roots will be conspicuous enough once they start growing. Also, some plants are genetically predisposed, even in the tropics, to stronger growth at certain times of the year - often it's in the rainy period. If the plant you're layering does exhibit cyclical growth patterns - try starting your layers about 1 month before you expect the strongest growth. It's difficult to suggest where you might be able to improve things if we don't know what you're doing. Watering an enclosed air layer daily sounds like a LOT of water, so you might be failing because you're asking the roots to transition back and forth between appropriate moisture levels to too wet; or, the medium might be consistently too wet. But that doesn't explain the dead branches. When you layer, you cut completely through the cambium down to the xylem. The plant can then still transport water and nutrients upward through the xylem to parts distal to the layer. Downward nutrient flow and polar flow of auxin terminates and collects in tissues immediately distal to the top ring of the layer, which is where roots should form. Tips: A) If you establish a layer on a branch or stem that isn't vertical, make your top and bottom cuts so they ARE horizontal. This means the cuts on a round branch that is say 10* to a vertical axis would be slightly elliptical, while a branch that's 60* to a vertical axis (30* to the horizon) would be would be much more elliptical. The reason for this is, the flow of auxin (stimulates rooting) is polar. Auxin will always find its way to the lowest part of a cut, which is where rooting will occur; and often, it might be the only root that grows from the layer site. You'd be better served if a multitude of roots emanated directly from the upper ring of your layer cut. B) You can help ensure success by applying a tourniquet immediately below wherever you want roots to grow on a branch. As soon as you see a bulge forming above the tourniquet, sprinkle an appropriate powdered rooting aid on the end of a piece of electrical tape. The rooting aid should cover enough tape to wrap one revolution around the layer site. The tape should be 2-3 times as long o/a as the part that's covered. Use a piece of string, a zip tie, or other method to secure the tape so it remains in place. Blanching (excluding light) the future layer site stimulates root initials to 'preform' and the rooting hormone and added moisture levels under the tape contribute significantly to the collective boost. You'll find a lot more info here. Al

What I've read about composting says that the juglone breaks down in about a year. Might take a little longer since compost provides a warmer, bacteria-rich environment to do the job. Or you could apply compost liberally to the area the trees occupied. Depending on where you live in MN, I might know someone interested (maybe a couple of someones!). PM sent. If you get no takers for the walnut here, you might try the GW Woodworking forum. It would be a shame to let beautiful wood like that go to waste! Here is a link that might be useful: Woodworking forum

It may be that the tree ran a root in your patch's general direction in the last 5 years...you don't know what is going on underground. Every year, those trees are gaining height and circumference both above and below ground. I have also gardened with 2 giant black walnut trees...I planted in a raised container and had no problems. My eighty-something grandfather had rhubarb planted in the same location for 50 years. 45 years ago, the neighbor planted a black walnut tree. about 4 years ago, grandpa's rhubarb started to wilt when it rained. He didn't know about juglone (despite his rockin green thumb) and last year when I pointed out the neighbor's tree and explained, he said, "Whell I'll bee!" He moved the rhubarb to the front flower bed, where it does great. I suspect the trees get to an age where they reach "killer" toxicity...perhaps more juvenile trees are not as much of a threat (that combined with the circumference, etc).

Thanks everyone for all the opinions, thoughts, and comments in this thread. It has been very interesting and I appreciate the comments. I still haven't reached a final decision on the tree, and I'll continue to take my time in making a decision but thought I'd give a sort of partial update. I do plan to get a quote for removing the tree (but not removing the stump or roots) in order to weigh my options fully, and I am planning to put the raised beds where I initially described, near the black walnut. However I have planned a supposedly juglone-tolerant vegetable garden for those raised beds, with a few exceptions just to see how they'll do. The beds themselves will be 4 4x8 beds; each bed is 1 ft tall. I am considering removing and replacing some of the soil below each bed, but I think that removing it on a large scale (up to a foot down as suggested) would not be practical for me. Instead, I'm considering using some kind of permeable barrier that would provide some drainage but would prevent roots from growing through. That may be overkill if the plants are juglone tolerant, but I am planning to experiment with a few juglone-sensitive plants in the areas farthest from the tree, so a barrier could help with that. If the tree is still standing late next summer when the walnuts start falling, I'm actually going to look into getting a bike helmet for my kid--thanks very much for this suggestion which I wouldn't have thought of on my own. It might sound silly to some, but those things are relatively big and heavy to be falling from so high, and a bit scary when you have a little one who likes to play in your garden (especially when she still had a soft spot right on top of her head!). A few folks have commented that it seems like black walnuts would be pretty light, but I'll just say this: my husband doesn't garden, so he doesn't really realize when the walnuts have started to fall. Instead, what happens is we'll be in the garage when we'll hear a BANG loud enough that my (usually mild-mannered) husband will jump and exclaim, "Holy &**$, what in the #$*$ was that!?" It really is quite alarming if you don't know what it is.