Walnut
Juglans regia
Botanical family: Juglandaceae
A large tree with a broad crown (Juglans regia, Juglandaceae family), grown for its nuts and its precious wood. Monoecious, it bears male catkins and discreet wind-pollinated female flowers, and its compound leaves are aromatic. Sources: Tela Botanica, “Juglans regia L.” (Coste's flora); Plants For A Future, “Juglans regia”.
Full sun
Deep, chalky
Moderate: water the young tree in dry spells in spring and summer
Hardy (~-25 °C), bud break and young growth sensitive to late frosts
Overwinters in your zone
Wind-pollinated (anemophilous)
Better crops with several plants or two varieties
Role in permaculture
Under its broad crown, better to grow plants with little sensitivity to juglone.
Poor companions
Allelopathy, reputed or observed: may slow some neighbours
Known pests & diseases
Pests and diseases that commonly affect this plant, tap to learn how to recognise and manage them.
Documented synergies
Relationships backed by a named source, with their real scope. A synergy without a named reference has no place here, no “it is said that…”.
The walnut releases juglone through its roots, leaves, and husk, a molecule that slows the germination and growth of sensitive species, including the Solanaceae (tomato, potato). But beware of the legend: the effect is strong in the laboratory, far more modest and disputed in the field. A field study did NOT find marked juglone allelopathy on understorey vegetation. To be taken seriously without dramatising.
scientific study
- · De Scisciolo B., Leopold D.J., Walton D.C. (1990), Journal of Chemical Ecology 16(4):1111-1130, DOI 10.1007/BF01021015
- · Medic A. et al. (2021), Agriculture 11(8):784, DOI 10.3390/agriculture11080784
A crucial distinction for a French garden: the heavy allelopathic reputation comes from the American BLACK walnut (Juglans nigra), the largest known juglone producer. The walnut of French orchards, however, is the common walnut (Juglans regia), which produces far less and rarely affects sensitive plants. Transferring the black walnut's reputation as-is to the walnut of our gardens is a frequent mistake.
scientific study
- · McCoy R.M. et al. (2018), Horticulture Research 5:67, DOI 10.1038/s41438-018-0067-5
The juglone in the soil is not uniform: more concentrated under the canopy, it decreases with distance and varies with the season. But there is NO universal measured 'toxic radius': the 15–18 m distance sometimes cited corresponds to the spread of the ROOTS of a large black walnut, not a boundary of toxicity. Better to observe your own plants than to trust a magic radius.
scientific study
- · Jose S., Gillespie A.R. (1998), Plant and Soil 203(2):191-197, DOI 10.1023/A:1004301309997
- · The Morton Arboretum, Black Walnut Toxicity (root zone of a large tree)
Seasons & availability
Walnuts: an autumn harvest, keeping well for a long time.
Available: January, February, March, September, October, November, December.
Guidance for the oceanic / temperate climate; it may vary with your region, altitude, exposure and growing method.
Sources
- Plants For A Future, « Juglans regia » (pfaf.org/user/Plant.aspx?LatinName=Juglans+regia)
- Interfel, « Noix : Présentation, disponibilité, conservation » (lesfruitsetlegumesfrais.com/fruits-legumes/fruits-a-coque/noix)
Nutritional & medicinal properties
For educational purposes. Not a substitute for medical advice. Effects depend on the form, the dose and personal context.
Precautions & contraindications
Possible allergen; a reminder of juglone in the garden.
In the kitchen & the apothecary
Where to find walnut in preparations: recipes and traditional herbal teas.
Species & varieties
The best-known species and varieties in France.
Species
Common varieties
Voices of peoples
Paraphrases attributed to their documented sources. Never an invented quote.
Greco-Roman antiquity · Mediterranean basin, 1st century AD
Pliny the Elder describes the walnut in his Natural History: its Latin name Juglans comes from Jovis glans, 'the acorn of Jupiter', the fruit of the gods, more noble than the mere acorn of the oak. Already at the time, Pliny observes that nothing grows in the shade of the walnut: 'its shade is heavy and oppressive, hostile to any cultivation around it'. The allelopathy of juglone was therefore noticed empirically two thousand years ago, well before it was isolated in the laboratory.
Pline l'Ancien, Naturalis Historia, livre XVII, chapitre 89 (composée vers 77 ap. J.-C.). Étymologie de Juglans (jovis glans).
Keep in mind
Poorly soluble in water, juglone does not travel far in the soil, and the real harm depends on soil type, drainage and the sensitivity of the neighbouring plant (Purdue Extension).
A note on rigour: many companion pairings are gardening folklore; this note sums up what the sources say, where there are any.
Key takeaways
- • Prefers full sun exposure.
- • Ideal soil: deep, chalky.
- • Keep away from: Tomato.