Black Walnut - Juglans Nigra - Companion Plants

Black Walnut - Juglans nigra - Tolerant Plants 

Black Walnut, Juglans nigra, is allelopathic, which means they secrete substances poisonous (probably juglones, although there has not been enough research to say for sure) to other plants. It is a great way of dealing with the competition and can make "companion" planting problematic. Below is a list of plants that either like being near a Black Walnut or just do not mind. It is not exhaustive, but its relative shortness gives a clue as to how effective Black Walnut is at discouraging close neighbours. The harmful effects are strongest on soil that is both wet and low in organic matter like sand or clay and weakest on well-drained, rich soil. After removing a Black Walnut tree, the soil will return to normal again surprisingly quickly. Some studies suggest as little as two months (but I would be inclined to leave it for a year - Ed).  

Well-composted material from black walnuts does not pose a problem, but to be on the safe side it is recommended not to use it for seeds and seedlings. You will often see advice saying that black walnut woodchips should be well aged before use as a mulch, but this is being overcautious as the wood itself contains very little juglone, apart from the bark, which is only really high in juglone during the growing season, and trees are typically felled in winter. Within a fortnight of being chipped, practically all of it will have decayed.

Annuals

Calendula officinalis, pot marigold,

Opomoea, Morning Glory

Viola wittrockiana, Pansy

Bulbs

Crocus

Eranthis hyemalis, winter aconite

Galanthus nivalis, snowdrop

Muscari botryoides, grape hyacinth

Narcissi / Daffodils

Scilla siberica, blue squill

Herbaceous Perennials

Ajuga reptans, Bugle

Astilbe

Campanula latifolia

Dryopteris cristata, Crested Wood Fern

Galium odoratum, Sweet Woodruff

Geranium sanguineum, Bloody Cranesbill/Geranium

Hemerocallis, Daylily

Heuchera varieties

Hosta fortunei

Hosta marginata

Hosta undulataIris sibirica

Monarda didyma

Phlox paniculata

Polemonium reptans, Jacobs ladder

Primula x polyantha, Primrose

Pulmonaria, Lungwort

Sedum spectabile, Stonecrop

Shrubs & Climbers

Clematis Red / Rouge Cardinal

Daphne mezereum

Hibiscus syriacus

Parthenocissus quinquefolia, Virginia creeper

Rhododendron Exbury hybrids