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Juglandaceae FAMILY Least Concern

Juglans nigra

Juglans nigra

Edibility
3/5
Medicinal
3/5

Safety & Hazards

The plant has occasionally been known to cause contact dermatitis in humans[1].

Cultivation Details

HabitDeciduous Tree
GrowthFast

The black walnut grows best areas with an annual precipitation from 30 to 130cm, an annual temperature in the range of 7 to 19°C and a pH from 4.9 - 8.2[2]. The dormant plant is very cold hardy, but the young growth in spring, however, can be damaged by late frosts. Requires a deep well-drained loam and a sunny position sheltered from strong winds[3, 4]. Prefers a slightly alkaline soil[5]. Plants are best suited to deep, rich, slightly acid or neutral soil, with good drainage, but will not grow well on infertile upland soil or on soils with poor drainage[2]. The Black walnut is one of the most valuable natural forest trees in the United States[2]. A very ornamental and fast growing plant[3, 5], it is sometimes cultivated in N. America for its edible seed. Whilst potential yields of 7.5 tonnes per hectare have been postulated, it is more feasible to expect annual yields of around 2.5 tonnes per hectare[2]. Good seed crops are usually produced every other year, though some plants fruit well annually whilst others produce god crops every third year[2]. The average weight of a seed from wild trees is about 17g, though there are many named varieties and the weight of their seeds varies from 20 - 30g[6, 2]. There are breeding programmes that are seeking to develop cultivars with thinner shells[7]. Trees in the wild commence bearing seeds when about 12 years old[8]. Black walnut trees mature their fruit rather generally throughout the plants natural range where there is a growing season of about 150 days and an average summer temperature of 16.5°C[2]. Trees do not fruit very freely in Britain unfortunately[3, 4]. They grow well in the eastern half of the country but often do not thrive in the west[9]. Trees have been extensively planted for timber in parts of C. and E. Europe[10]. This species hybridizes with Juglans regia[11], some named cultivars have been developed from this cross for their seed. Plants produce a deep taproot which makes them very drought resistant when established, though they are intolerant of root disturbance[3, 4, 2]. Seedlings should be planted out into their permanent positions as soon as possible and given some protection for their first winter or two since they are somewhat tender when young[3, 4]. Flower initiation depends upon suitable conditions in the previous summer[5]. The flowers and young growths can be destroyed by even short periods down to -2°c, but fortunately plants are usually late coming into leaf[5]. The black walnut is self-fertile, but the sequence of male and female blooming, called dichogamy, can and often does minimize chances of a tree shedding pollen on its own pistils. In different trees pollen may be shed before the receptivity period of female flowers, or at same time, or after pistil receptivity. For greatest possible nut production, plant trees of 2 or more cvs, as different cvs have overlapping pollen-receptivity periods and can pollinate each other[2]. Any pruning should only be carried out in late summer to early autumn or when the plant is fully dormant otherwise wounds will bleed profusely and this will severely weaken the tree[5]. Plants produce chemicals which can inhibit the growth of other plants. These chemicals are dissolved out of the leaves when it rains and are washed down to the ground below, reducing the growth of plants under the tree[12, 13, 14]. The roots also produce substances that are toxic to many plant species, especially apples (Malus species), members of the Ericaceae, Potentilla spp and the white pines (certain Pinus spp.)[5]. Beans, peas and tomatoes are also particularly sensitive to these secretions and will not grow in the rooting zone[5]. Trees cast quite a dense shade so, along with their other anti-social tendencies, are not very friendly trees for a woodland garden[PFAF]. The bruised leaves have a pleasant sweet though resinous smell[15].

Propagation

The seed is best sown as soon as it is ripe in individual deep pots in a cold frame[16]. You need to protect it from mice, birds, squirrels etc. The seed usually germinates in late winter or the spring. Plant out the seedlings into their permanent positions in early summer and give some protection from the cold for their first winter or two. The seed can also be stored in cool moist conditions (such s the salad compartment of a fridge) over the winter and sown in early spring but it may then require a period of cold stratification before it will germinate[17, 16, 18]. Cite as: Temperate Plants Database, Ken Fern. temperate.theferns.info. 2026-02-21. <temperate.theferns.info/plant/Juglans+nigra>

Pollinators

Wind

References

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  2. [2]Handbook of Energy Crops — Duke. J. · - · 1983 · https://hort.purdue.edu/newcrop/duke_energy/dukeindex.html · ISBN - ↩︎Published only on the Internet, excellent information on a wide range of both temperate and tropical plants.
  3. [3]RHS Dictionary of Plants plus Supplement. 1956 — F. Chittendon. · Oxford University Press · 1951 · ISBN - ↩︎Comprehensive listing of species and how to grow them. Somewhat outdated, it has been replaced in 1992 by a new dictionary (see [ 200 ]).
  4. [4]Trees and Shrubs Hardy in Great Britain. Vol 1 - 4 and Supplement. — Bean. W. · Murray · 1981 · ISBN - ↩︎A classic with a wealth of information on the plants, but poor on pictures.
  5. [5]The New RHS Dictionary of Gardening. 1992. — Huxley. A. · MacMillan Press · 1992 · ISBN 0-333-47494-5 ↩︎Excellent and very comprehensive, though it contains a number of silly mistakes. Readable yet also very detailed.
  6. [6]Cornucopia - A Source Book of Edible Plants. — Facciola. S. · Kampong Publications · 1990 · ISBN 0-9628087-0-9 ↩︎Excellent. Contains a very wide range of conventional and unconventional food plants (including tropical) and where they can be obtained (mainly N. American nurseries but also research institutes and a lot of other nurseries from around the world.
  7. [7]Identification Guide to the Trees of Canada — Lauriault. J. · Fitzhenry and Whiteside, Ontario. · 1989 · ISBN 0889025649 ↩︎Very good on identification for non-experts, the book also has a lot of information on plant uses.
  8. [8]Trees of North Texas — Vines. R.A. · University of Texas Press. · 1982 · ISBN 0292780206 ↩︎A readable guide to the area, it contains descriptions of the plants and their habitats with quite a bit of information on plant uses.
  9. [9]Seed Manual for Ornamental Trees and Shrubs. — Gordon. A. G. and Rowe. D. C. F. · HMSO; London · 1982 · ISBN 0-11-710152-4 ↩︎Very comprehensive guide to growing trees and shrubs from seed. Not for the casual reader.
  10. [10]Flora Europaea — ? · Cambridge University Press · 1964 · ISBN - ↩︎An immense work in 6 volumes (including the index). The standard reference flora for Europe, it is very terse though and with very little extra information. Not for the casual reader.
  11. [11]Trees of Central Texas. — Vines. R. A. · University of Texas Press · 1987 · ISBN 0-292-78958-3 ↩︎A good concise guide, it gives details of habitats and some of the uses of trees growing in Texas.
  12. [12]Companion Plants. — Philbrick H. and Gregg R. B. · Watkins · 1979 · ISBN - ↩︎Details of beneficial and antagonistic relationships between neighbouring plants.
  13. [13]Companion Planting for Successful Gardening. — Riotte. L. · Garden Way, Vermont, USA. · 1978 · ISBN 0-88266-064-0 ↩︎Fairly good.
  14. [14]Wild Food Plants of Indiana. — McPherson. A. and S. · Indiana University Press · 1977 · ISBN 0-253-28925-4 ↩︎A nice pocket guide to this region of America.
  15. [15]Scented Flora of the World. — Genders. R. · Robert Hale. London. · 1994 · ISBN 0-7090-5440-8 ↩︎An excellent, comprehensive book on scented plants giving a few other plant uses and brief cultivation details. There are no illustrations.
  16. [16]Hardy Woody Plants from Seed. — McMillan-Browse. P. · Grower Books · 1985 · ISBN 0-901361-21-6 ↩︎Does not deal with many species but it is very comprehensive on those that it does cover. Not for casual reading.
  17. [17]Propagation of Trees, Shrubs and Conifers. — Sheat. W. G. · MacMillan and Co · 1948 · ISBN - ↩︎A bit dated but a good book on propagation techniques with specific details for a wide range of plants.
  18. [18]The Reference Manual of Woody Plant Propagation. — Dirr. M. A. and Heuser. M. W. · Athens Ga. Varsity Press · 1987 · ISBN 0942375009 ↩︎A very detailed book on propagating trees. Not for the casual reader.
  19. [19]IUCN Red List of Threatened Species — http://www.iucnredlist.org/ ↩︎A list of plants under threat and facing possible extinction, usually with brief details of the threats and information on habitat.
  20. [20]New Trees — Grimshaw J.; Bayton R.; Wilks H. · Kew Publishing; London · 2009 · ISBN 1842461737 ↩︎Provides comprehensive botanical descriptions and horticultural commentary on over 800 tree species that have been introduced to cultivation in recent decades.
  21. [21]Gray's Manual of Botany.Eighth Edition — Fernald. M. L. · American Book Co.; New York · 1950 · ISBN 0442222505 ↩︎A bit dated but a good and concise flora of the eastern part of N. America.
  22. [22]Manual of the Trees of N. America. — Sargent. C. S. · Dover Publications Inc. New York. · 1965 · http://www.biodiversitylibrary.org/ · ISBN 0-486-20278-X ↩︎Two volumes, a comprehensive listing of N. American trees though a bit out of date now. Good details on habitats, some details on plant uses. Not really for the casual reader. It can be downloaded from the internet.
  23. [23]The Complete Trees of N. America. Field Guide and Natural History. — Elias. T. · Van Nostrand Reinhold Co. · 1980 · ISBN 0442238622 ↩︎A very good concise guide. Gives habitats, good descriptions, maps showing distribution and a few of the uses. It also includes the many shrubs that occasionally reach tree proportions.
  24. [24]Flora of N. America — http://flora.huh.harvard.edu/fna/ ↩︎An on-line version of the flora with an excellent description of the plant including a brief mention of plant uses.
  25. [25]Sturtevant's Edible Plants of the World. — Hedrick. U. P. · Dover Publications · 1972 · ISBN 0-486-20459-6 ↩︎Lots of entries, quite a lot of information in most entries and references.
  26. [26]The Oxford Book of Food Plants. — Harrison. S. Wallis. M. Masefield. G. · Oxford University Press · 1975 · ISBN - ↩︎Good drawings of some of the more common food plants from around the world. Not much information though.
  27. [27]Edible Wild Fruits and Nuts of Canada. — Turner. N. J. and Szczawinski. A. · National Museum of Natural Sciences · 1978 · ISBN - ↩︎A very readable guide to some wild foods of Canada.
  28. [28]Native Harvests. — Kavasch. B. · Vintage Books · 1979 · ISBN 0-394-72811-4 ↩︎Another guide to the wild foods of America.
  29. [29]A Modern Herbal. — Grieve. · Penguin · 1984 · ISBN 0-14-046-440-9 ↩︎Not so modern (1930's?) but lots of information, mainly temperate plants.
  30. [30]A Field Guide to Medicinal Plants. Eastern and Central N. America. — Foster. S. & Duke. J. A. · Houghton Mifflin Co. · 1990 · ISBN 0395467225 ↩︎A concise book dealing with almost 500 species. A line drawing of each plant is included plus colour photographs of about 100 species. Very good as a field guide, it only gives brief details about the plants medicinal properties.
  31. [31]Native American Ethnobotany — Moerman. D. · Timber Press. Oregon. · 1998 · ISBN 0-88192-453-9 ↩︎Very comprehensive but terse guide to the native uses of plants. Excellent bibliography, fully referenced to each plant, giving a pathway to further information. Not for the casual reader.
  32. [32]The Herb Book. — Lust. J. · Bantam books · 1983 · ISBN 0-553-23827-2 ↩︎Lots of information tightly crammed into a fairly small book.
  33. [33]Complete Guide to Herbs. — Holtom. J. and Hylton. W. · Rodale Press · 1979 · ISBN 0-87857-262-7 ↩︎A good herbal.
  34. [34]Plants for Man. — Schery. R. W. ↩︎Fairly readable but not very comprehensive. Deals with plants from around the world.
  35. [35]A Weavers Garden — Buchanan. R. · McGraw-Hill Contemporary · 1987 · ISBN 0934026289 ↩︎Covers all aspects of growing your own clothes, from fibre plants to dyes.
  36. [36]Nature's Colors - Dyes from Plants. — Grae. I. · MacMillan Publishing Co. New York. · 1974 · ISBN 0-02-544950-8 ↩︎A very good and readable book on dyeing.
  37. [37]CosIng — http://ec.europa.eu/growth/tools-databases/cosing/ ↩︎CosIng is the European Commission database for information on cosmetic substances and ingredients.
  38. [38]A - Z of Companion Planting. — Allardice.P. · Cassell Publishers Ltd. · 1993 · ISBN 0-304-34324-2 ↩︎A well produced and very readable book.
  39. [39]Commonsense Compost Making. — Bruce. M. E. · Faber · 1977 · ISBN 0-571-09990-4 ↩︎Excellent little booklet dealing with how to make compost by using herbs to activate the heap. Gives full details of the herbs that are used.
  40. [40]Dictionary of Economic Plants. — Uphof. J. C. Th. · Weinheim · 1959 · ISBN - ↩︎An excellent and very comprehensive guide but it only gives very short descriptions of the uses without any details of how to utilize the plants. Not for the casual reader.
  41. [41]A Dictionary of Plants Used by Man. — Usher. G. · Constable · 1974 · ISBN 0094579202 ↩︎Forget the sexist title, this is one of the best books on the subject. Lists a very extensive range of useful plants from around the world with very brief details of the uses. Not for the casual reader.
  42. [42]An Illustrated Flora of the Northern United States and Canada — Britton. N. L. Brown. A. · Dover Publications. New York. · 1970 · ISBN 0-486-22642-5 ↩︎Reprint of a 1913 Flora, but still a very useful book.
  43. [PFAF]Plants for a Future — pfaf.org ↩︎