"Or I could just let it grow and worry about it next year." I can not recommend that procedure. I tried that last year! I had such a problem getting everything planted (two feet of rain between thaw and normal planting time), that, by the time I got around to dealing with weeds, it was too hot for me to expend the energy to clean everything up. (I have a heart condition, pacemaker, and can not do much "heavy lifting", or even steady work without very frequent rests, and working very hard in 100F temperatures is not possible.) It was just so hopeless out there with crabgrass in my asparagus (the neighbor on that side of my garden uses crabgrass as the variety of choice for his lawn), I let it go. I have just been greeted with the results of that: crabgrass sprouting everywhere! I had a drier spring this year, and had almost everything planted on time, and have had cool enough weather that I have the crabgrass and other weeds under control. I used the hoeing and pulling method, but I will use some pre-emergent in the future. If it gets too hot and I keep having more crabgrass sprout before I find the pre-emergent, I will use "roundup". I will use a cheap paintbrush and paint the seedlings with it. I am not afraid of roundup. I was able to defeat it in my bluegrass lawn by painting some encroaching sprigs of it with a small artist brush using a "roundup" substitute, and the space I garden in now, was the backyard of a neighboring house that had a Bermuda grass lawn that I sprayed several times over about a two month period the year I bought it (and a few sprigs sometimes for the next several years. I have not had any appear for quite a while now, and never killed any desirable plants or lawn grass with it.

it depends on the biological activity in the soil, and also where the leftover roots are. near a root is much worse than away. Juglone lasts hours in the presence of some common bacteria, but it lasts year in heavy, barren soils. If you want to do your best, till the area, tilling in good amounts of undigested OM (leaves, but manure or grass clippings or hay or straw would do too). That will create a bacteria rich soil, nicely prepare the bed for the asp, and you will be safer next spring.

There are many good fact sheets on the Web regarding juglone toxicity, but I'll attach a helpful one. It's worth noting that walnut leaves CAN be composted as long as you don't intend to use it right away. Also the allelopathic chemicals come from just about all parts of the plant, including the roots and run-off from the branches and leaves. Here is a link that might be useful: Click here for some good information

I, too have issues with the Evil trees - I have neighbors on either side who have 2 full grown trees each! I only have space for one dwarf peach tree because of all the shade (I do have several bushes & small trees like Rose of Sharon). I've been here 18 years now and have learned a thing or two about gardening under these trees since it's either the roots putting out the poison or the dripline killing my plants. It took me years to figure out the rain barrels I was using for the veggie garden was truly wiping out my tomatoes & cucumbers every season by the 4th of July & now I use straw bales to grow them so the poison doesn't touch them. I've found a lot of plants they say will work, don't & a lot that do. It's a matter of trial & error. I remove the plants asap when I notice them succumbing to poison & rinse off the roots thoroughly, then plant in new soil elsewhere (If I can save them in time). Sometimes it works, sometimes not. Ive lost all my Columbine except the wild Michigan ones that are protected- my Mom's friend received permission to take some, & I got her "extras", too! So, I'm helping save a protected species while getting columbines in my gardens! Yay!!! Feel free to contact me to ask any questions. Here's a great link to get you started (tho I have plants growing that here say no & plants that should but don't...): https://www.oakgov.com/msu/Documents/publications/oc0280_black_walnut.pdf