We have a lot of "juglone areas" in our yard too because of black walnut trees. There are many juglone-tolerant shrubs, but wanted to find out if you know what kind of soil (clay, sandy, loam, etc.) your shrub would be growing in, and what the moisture level is in the area you want to plant.

Also, have you tested the PH of the soil to find out if the soil you want to plant in is acid or more alkaline?

2 hours of sun a day or less is usually considered shade, rather than part shade. Part shade would be between 2 and 6 hours. You'll need a shrub that does well in shade.

Is the shade from a building or other structure? Or from overhead trees?

The tree just came down on Monday, and it's been cloudy/rainy since then, so I have not counted exactly how many hours of sun it gets. But it probably counts as shade, or just barely into part-shade territory. The spot is between two houses, and is also partly shaded by a linden tree, so it doesn't have much of a chance to get direct sun.

I've seen young, black walnut saplings completely regenerate and grow back as saplings and small trees after having been cut to the ground, year after year, because black walnut has such a strong and deep taproot. It's very difficult to get the taproot out, unless you destroy it with Roundup or something. However, I don't have any experience with cutting down a mature, full-size black walnut tree. Since laceyvail has 40 years of gardening experience, I trust her opinion that the juglone will be gone in a year. I assume that a mature black walnut will not regenerate from the roots.

A shrub that may work for you in the meantime is the Maple-leaved Viburnum (Viburnum acerifolium). It's resistant to juglone, will tolerate partial shade to shade, will tolerate clay soil, and is a medium-size shrub. The leaves get a very showy, attractive reddish-magenta-purple color in autumn. Hardy to your Zone in Boston.

It's not the most stunning ornamental-type shrub, as compared to say, a rhododendron or azalea—it looks rather "woods-y"—but the Maple-leaved Viburnum can be a nice background shrub for shade perennials in front of it. It gets pretty white flowers, and purple berries. It suckers freely, and gets about 4 to 6 feet in cultivated situations, so you will need to prune. If you can't find it in a local nursery, you can order it online. I would wait until the fall to plant.

Maple-leaved Viburnum may be a bit of a gamble depending on just how shaded the spot is under your Linden tree and between the two buildings. It will flower better and produce more berries with more sun than you may have available in this spot, but most people say it does okay even in shade.

Ours seem fine in partial shade in proximity to black walnut saplings, but again, we don't have a full-size mature black walnut tree in our yard. Yet!

We also have wild grape (Vitis riparia) that do fine in close proximity to black walnut saplings in partial shade and clay soil, but the wild grape may be a bit messy-looking in a formal Boston garden, and will inevitably climb up your Linden tree.

NOTE: There are other types of Viburnum that are listed as being SUSCEPTIBLE to juglone, such as the Viburnum sieboldii, Viburnum dentatum, Viburnum opulus, and Viburnum plictum, so be sure not to get any of these.

There are also a number of other native New England shrubs, as well as Asian and European shrubs that are listed as resistant to juglone. The Maple-leaved Viburnum and the Wild Grape are the only ones I have any personal experience with. Many of these other shrubs are either too large for your area, prefer sandy soil, or need more sun than you have in this spot. Some are banned in Massachusetts, such as Japanese Barberry (Berberis thunbergii).

You can also contact the New England Wild Flower Society for more info on juglone-resistant shrubs at the link below.

Hope this helps!
-topie

Many of these shrubs below require full sun, or a sandy soil, or may not tolerate clay soils. Some are creepers that become very very large. List contains both U.S. native and non-native shrubs.

American Barberry (Berberis canadensis) 4-6 ft tall, Full Sun.

Climbing Bittersweet (Celastrus scandens) Climber; 20-30 ft long; full sun to partial shade; needs climbing support.

Virgin's Bower (Clematis virginiana) Climber; 12-15 ft long; full sun to partial shade; aggressive spreader; leaves cause skin irritation if touched; needs climbing support.

Forsythia: Native to eastern Asia; 3 to 9 ft. tall; full sun to partial shade.

Smooth Hydrangea (Hydrangea arborescens): 3 to 5 feet tall; partial shade; hardy from zones 3 to 9 but native to more southern areas of U.S. than Massachusetts; needs a moist soil; susceptible to numerous diseases such as bud blight, bacterial wilt, leaf spot, rust and powdery mildew.

Shrubby St.John's wort (Hypericum prolificum): 2 to 3 feet tall; full sun to partial shade; prefers rocky, sandy soils.

Kerria (Kerria japonica): Native to China and Japan; 4 to 8 feet tall; partial shade.

Pasture Rose, Carolina Rose (Rosa carolina): 1 to 3 feet tall; full sun to partial shade; prefers sandy soils.

PERENNIALS:
For partial shade or shade, reported juglone-tolerant. Not all are necessarily clay soil tolerant. The ones we grow successfully in clay have a (*) next to their name:

Dogtooth violet (Erythronium americanum)

Great Blue Lobelia (Lobelia siphilitica)

* Jack in the pulpit (Arisaema triphyllum)

Mayapple (Podophyllum peltatum)

Trillium

* Virginia springbeauty (Claytonia virginica)

* Violet (Viola)

FERNS:
Christmas fern (Polystichum acrostichoides)

* Ladyfern (Athyrium filix-femina) ours are ok

Buckler fern/Wood fern (Dryopteris cristata)

Sensitive fern (Onoclea sensibilis)

I'm thinking about the Hydrangea arborescens, but am not sure because they are prone to so many problems.

One last note: I've read that English boxwood (Buxus sempervirens) is juglone-tolerant, but I'm not sure how well it would do in your level of shade. I think it has to be thinned extensively in shadier situations to prevent fungal diseases. Never have planted a boxwood myself, but it could be an option for you, and would look nice in a formal type of garden setting. If you like boxwoods, I would ask someone else that knows more about them if boxwood would work in shade.

Good luck!