Walnut Guild 🌳

A large black walnut tree lives in the back yard.

I would like to find California native companion plants for it, but have had a difficult time.

Something about the soil makes me think it’s poor. It’s clay to begin with, but also full of gravel, construction debris and covered by barrier plastic and pea gravel, pavers and bricks in many places. Few things grow well.

The walnut and neighboring buildings cast the yard in shade. California is frequently in drought, so it’s dry. I’ve recently learned walnuts are allelopathic, releasing the toxin juglone. An arborist we consulted regarding the health of the walnut wasn’t too concerned about juglone toxicity wrt other trees in the yard, fwiw.

The Black Walnut Dispatch inspires me to take and share notes so we might all learn together.

The permaculture discipline has also been helpful, not least because it has many handy phrases like guild (recreations of plant communities found in nature) and companion plants (symbiotic or mutually supportive), and concepts like a seven-layer garden and soil building.

I’ve found Gaia’s Garden by Toby Hemenway a concise introduction to permaculture, and it even has an in-depth description of a walnut guild!

Paul Stamets, a hero, is a fan of permaculture and proposes a Stametsian Model with an eighth layer for fungi.

Las Pilitas Nursary is a rich source of native plant and permaculture information. CNPS also enables us to search shade plants by zipcode. Lists of juglone-tolerant species abound, eg 1.

So, the challenge is: build a juglone-, drought- and shade-tolerant California native guild around the walnut.

Here are the plants I’ve tried:

Latin name Common name Layer Health* Proximity* Sun* Water* Notes
Achillea millefolium californica California yarrow Herb 3 1 4 1 Suspect more sun needed, but one in the front yard in shade is fuller. Juglone tolerant per 1
Allium triquetrum Three-cornered leek Herb 5 1 2-4 1 Self-propagating. Juglone tolerant per 1. Curious to try a native Allium like Allium unifolium
Agapanthus praecox orientalis Lilly of the Nile Shrub 2 1 3 1 This was doing well, but then started yellowing. Agapanthus is prolific in the front yard in shade, for comparison
Aquilegia eximia Serpentine columbine Shrub 1 1 2 2 The columbine’s health steadily declined after planting, dropping leaves and never flowering.
Artemisia douglasiana California Mugwort Herb 2 2 4 1 Leaves look good, but growth is slow. Suspecting it needs more water
Asarum caudatum Western wild ginger Root 4 3 2 2 Leaves look good, but growth is slow and it hasn’t flowered. I suspect it needs more water
Brugmansia arborea Trumpet flower Low tree 4 2 4 1 Flowering and leaves look good. Suspect more sun needed
Callistemon rigidus Bottlebrush tree Low tree 5 3 4 1 Flowers profusely year-round
Citrus tangerina Tangerine tree Low tree 2 1 3 1 The tree produces inedible fruit and its leaves are chlorotic and sparse :( I suspect it gets insufficient sun. An arborist mentioned citrus trees are “hungry”, so this one may just need fertilizer. There’s a lemon tree in the front yard that looks great, for comparison
Camellia japonica Camelia Low tree 1 & 5 3 2-3 2 Two camellias on the property outside dripline. One in good health, but one suddenly whithered. Suspecting gophers although they left the other alone.
Claytonia sibirica Candy flower Herb 5 3 2 2 Leaves and growth look good
Clinopodium douglasii Yerba buena Ground 4 1 2 2 Leaves look good, but growth is slow
Dietes iridioides African iris Shrub 5 1 3 1 Flowers and seeds readily. Juglone tolerant per 1
Festuca californica California fescue Ground   1 2 1 New planting🤞
Fragaria californica Wild strawberry Ground 3 1 3 1 Spreading and leaves look good, but not flowering. Suspect more sun needed
Hedera helix English ivy Vine 5 2 3 1 Well-established when I moved in. Grows vigorously on wall at dripline. Less vigorously inside dripline
Heracleum maximum Cow parsnip Shrub 3 1 2 2 Under dripline. Planted two and both died back, but one returned when the rains came. Leaves good so far
Holodiscus discolor Cream bush Shrub 4 1 2 2 Leaves look good, but slow growing
Horkelia californica California horkelia Ground 4 1 3 1 Hasn’t flowered or spread. Suspect more sun needed
Hydrangea macrophylla Hydrangea Shrub 1 3 3 1 A tall shrub growing in shade when I moved in. Declining health perhaps due to low water or sun
Iris douglasiana Douglas Iris Shrub 4 1 3 1 Planted two. One died. The other’s leaves look good, but it hasn’t flowered. There’s another iris nearby that’s flowering, for comparison. Juglone tolerant per 1
Ligustrum japonicum Japanese Privet Low tree 5 1 2 1 Predates me. Healthy/invasive.
Lupinus arboreus Yellow bush lupine Shrub   1 4 1 New planting in a relatively sunny spot🤞 I read somewhere nitrogen fixers are generally juglone-tolerant
Lupinus variicolor Varied lupine Shrub   1 4 1 As above
Mimulus aurantiacus Bush monkeyflower Shrub 4 3 2 1 Planted in shade. Leaves and growth look good, but waiting for flowers
Mimulus aurantiacus Bush monkeyflower var ? Shrub 4 1 3 1 A lower, spreading mimulus. Leaves and growth look good, but waiting for flowers
Nandina domestica Heavenly bamboo Shrub 5 2 3-4 1 Leaves look healthy.
Oxalis pes-caprae Sourgrass Herb 5 1 2-4 1-2 Under dripline. It’s invasive, but in the spirit of permaculture I’m trying to learn from it. Makes me want to try a native oxalis like Oxalis oregana
Pittosporum eugenioides Tarata Low tree 5 1 2 1 Predates me. Healthy. Looks like a volunteer.
Pittosporum tobira Mock orange Low tree 5 3 5 1 Flowering and leaves look good
Prunus cerasifera Purple leaf ornamental plum Low tree 3 1 3 1 I think this is a plum. The tree leaves regularly, but hasn’t flowered and has dying branches. I suspect it was planted when the walnut was smaller and let more light through.
Plantago subnuda Tall coastal plantain Herb   1 2 2 New planting🤞
Rudbeckia californica California coneflower Shrub 5 1 4 1 Planted in a pot (away from slugs) but in range of leaf fall
Stachys bullata Wood mint Herb   1 2 2 New planting🤞 Juglone-tolerant per 2
Symphyotrichum chilense California aster Shrub 4 3 3 1 Leaves look good, slow growing
Taraxacum officinale Dandelion Herb 4 1 3 1 Self-propagating. Leaves look good. If it flowers and spreads, I’ll increase the health grade to 5

* Numeric ranges:

Footnotes

  1. Landscaping and Gardening Around Walnuts and Other Juglone Producing Plants  2 3 4 5

  2. Plants Resistant to Walnut Toxicity 

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