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Mature Black Walnut Tree Juglans nigra Options
100-150cm: 5-7L pot. 1-2 years old.
120-180cm: 7-12L pot. 2-4 years old. Half standard. 2-3 years old.
Girth 8-10cm: Standard, *roughly 240-300cm tall.
Girth 10-12cm: Standard, *roughly 300-360cm tall.
Girth 12-14cm: Standard, *roughly 360-420cm tall.
Girth 14-16cm: Standard, *roughly 420-480cm tall.
Girth 16-18cm: Standard, 90L pot, *roughly 480-500cm tall.
Girth 18-20cm: Standard, 90-110L pot, *roughly 500-520cm tall.
Girth 20-25cm: Standard, 120-150L pot, *roughly 520-540cm tall.
*Heights are given as a very rough guideline and can have considerable variation based on species and supplier. Each nursery experiences different growing conditions. Trees may also have been pruned before being sent out, so we can only guarantee girth. Trees over 5.5m may include a delivery surcharge based on location and species.
A Juglans Nigra listed as "standard" will have around 180-200cm of clear stem. A half standard will have around 80-100cm of clear stem.
Each 2cm of girth very roughly represents 12-18 months growth.
Black Walnut Tree, A Huge American Walnut for Parkland, Estates and Very Large Gardens
Black Walnut Tree, Juglans nigra, is a large American walnut species for buyers who want an impressive long-term specimen tree with bold foliage, dark ridged bark, edible nuts and valuable timber interest. It has RHS Award of Garden Merit status and is also known as Eastern Black Walnut or American Walnut.
This is not a small garden walnut. Black Walnut is a very large, vigorous, broad-crowned tree, with Woodland Trust giving a mature height of around 30-40m. It is best suited to very large gardens, estates, parkland or open spaces where it has room to develop properly.
Black Walnut has strong ornamental value as well as practical value. It produces large pinnate leaves, aromatic foliage when crushed, dark heavily ridged bark and yellow to bronze autumn colour. Over time, it becomes a large shade tree with real presence.
Black Walnut is somewhere between partially self-fertile and self-fertile, meaning it is likely to provide nuts without the need for another walnut nearby, but a full flush of walnuts is more likely if there is. A second Juglans nigra Black Walnut nearby will provide additional pollen and should improve the size of your crop. We know this is counter-intuitive to normal cross-pollination practices, but walnut pollination works differently.
The nuts are edible and have a strong, distinctive flavour, but they are not as convenient as common walnuts. The shells are much harder and the kernels are harder to extract. Black Walnut is best used as a large ornamental, shade and timber-interest tree.
Pests and diseases: Black Walnut is generally a tough, hardy tree once established, but it should still be planted well. Give it full sun, space, good soil and low competition while it settles in. Routine pruning is usually limited to removing dead, damaged or badly placed growth.
Planting a Black Walnut Tree
Plant Black Walnut Tree in full sun, in deep, fertile, well-drained soil. It needs open space and should not be crowded by buildings, other trees or heavy grass and weed competition while young.
Black Walnut is deep-rooting and develops a strong taproot, so careful planting is important. Set the tree at the same depth it was growing in the pot, backfill with soil, firm gently and water thoroughly. Keep it watered during dry spells in the first growing season, and keep grass and weeds away from the base while it establishes.
Young trees may also need protection from deer, rabbits or other browsing animals where these are a problem. Once established, Black Walnut becomes a strong, substantial tree, but the early settling-in period matters.
Useful Information About Black Walnut Tree
Black Walnut is native to central and eastern North America and is non-native in Britain. It has long been valued for its dark, attractive timber, which is one reason the species is so well known. The wood is often described as fine, straight-grained and dark, making it one of the best-known timber walnuts.
The shells and hulls have also had practical uses, including abrasives and dye. The kernels are used in baking and confectionery, but the hard shells mean this is a walnut for patient people, nutcrackers and possibly mild stubbornness.
Black Walnut can also affect nearby planting because walnuts produce a compound called juglone and others that may suppress some plants growing close to them. For most buyers, the practical point is simple: give it space, avoid planting it in a cramped mixed border, and treat it as a serious long-term tree for a large site.
It is also a useful tree for wildlife. The nuts are eaten by squirrels and some birds, and the tree provides a large canopy and habitat value as it matures. That is good news if you are planting for biodiversity, but less good if your main ambition is to keep every nut for yourself. Squirrels are likely to show professional interest.
If you are looking for more than one tree, e.g. setting up an orchard, then take a peek at WHOLESALE WALNUT TREES where you will receive large discounts for bulk purchases.
Ornamental Tree Roots In The Shade e.g. Behind A Fence
It is more important that that foliage (posh term for leaves) receives the sunlight than the roots. So if the canopy of your ornamental tree can sunbathe but the bottom of your tree thinks there has been a nuclear winter then that is ok. You might want to ensure you have good drainage as water and no sun is the start of algae and other such issues.
Do I Need To Stake My Ornamental Tree?
Our article on Tree Staking should help guide you.
Planting In The Corner Of A Garden
Air and light is reduced in this location which could promote fungus and bacterial issues. If the corner is of the house and a fence then you also have leeching issues to contend with from cement and wood preservatives. Also when it rains, that area would experience higher water levels so we advise against it unless the plant is very hardy.
General Walnut Information
Walnuts can be difficult to establish in their first year, and some shoot-tip dieback can happen while young trees settle in. To improve their chances, water well during dry spells and keep grass and weeds cleared from around the base of the tree, ideally to about 1 metre across. Walnut trees tolerate a range of soils, but they establish best in deep, fertile, well-drained soil in a sunny, sheltered position.
Most walnut trees sold for fruit are grafted rather than grown from seed. Grafted walnut trees usually give more predictable variety characteristics, better size and shape consistency, and earlier cropping than seed-grown walnuts. Some grafted walnut varieties can start cropping within a few years of planting, depending on the variety, tree size, growing conditions and establishment.
If you are going to pickle walnuts, pick them in late June or early July, before the shell has properly hardened.
To improve fruiting, some growers use a technique called girdling, ringing or cincturing. This deliberately restricts the flow of sap to reduce vegetative growth and encourage fruiting. It must be treated with caution: if done too tightly, too deeply, for too long, or in the wrong place, it can damage or even kill the tree. RHS notes that ringing is used in fruit production but is not advised for home gardeners because of the risk if done incorrectly. Anyone considering it should research the technique properly first and understand the risk before trying it.
Ideal conditions for walnut trees are deep, fertile, moisture-retentive but well-drained soil, full sun, shelter from strong winds and avoidance of frost pockets. If the soil is poor, improve the wider planting area with well-rotted organic matter rather than creating a rich isolated pocket in the planting hole.
Walnuts are large trees, so check the expected mature size of the variety before planting. Many need a generous open position rather than a small garden corner. A nitrogen-rich feed or a quality mulch in early spring can help keep the tree healthy, especially while it is establishing.
Walnut shells have interesting uses in industry. They are used for cleaning and polishing materials such as soft metals, plastics, wood, stone and fibreglass.
Walnut trees can produce juglone, a natural compound that may suppress the growth of some nearby plants. The issue is generally associated more strongly with black walnut, Juglans nigra, but English/Persian walnut, Juglans regia, can still produce juglone to a lesser degree. Avoid planting very sensitive plants directly beneath or very close to walnut trees, especially under the canopy where roots, fallen leaves and husks are concentrated. Shade, dry soil and root competition can also make planting under an older walnut difficult.
Seed-grown Juglans regia can take many years to crop, which is one reason grafted walnut varieties are usually preferred for fruit production.
Walnuts are one of the oldest tree foods known to have been used by people, with records commonly traced back thousands of years. The common walnut is often associated with Persia and the wider region around modern Iran, and walnut trees were introduced to Britain by the Romans.
Walnut trees can be long-lived, and established trees may remain productive for many decades in good conditions.
Walnuts are energy-dense and contain unsaturated fats, protein, fibre, vitamins and minerals. Per 100g of shelled walnut, they contain approximately:
65g of fat, most of which is unsaturated fat
15g of protein
14g carbohydrates
7g dietary fibre
Calories per 100g: around 650
Per 100g of shelled walnut, they also contain approximately:
441mg potassium
346mg phosphorus
158mg magnesium
98mg calcium
3.4mg manganese
3.1mg zinc
2.9mg iron
1.6mg copper
98µg folate
0.54mg vitamin B6
0.34mg thiamin
General Walnut Tree Pollination
All walnut trees have male catkins and female flowers. In a perfect world, the male pollen release happens at the same time as the female flowers are ready to accept it and maximum pollination occurs giving largest possible walnut fruit harvest. Some walnuts have a time gap between the males releasing pollen to the females being ready to accept it i.e. smaller crop. By having another walnut tree that releases pollen at the same time as your female flowers are ready to accept it, you can increase the size of your walnut crop.
Unfortunately, pollination is not always a two way process like apples and other fruits so some combinations may mean only one tree has increased fruit yield. Our suggestions for partners give you maximum harvest size.
General Walnut Tree Pruning
Walnut trees need less pruning than apples, pears or plums. The aim is to build a strong, open tree, remove badly placed growth and avoid heavy cutting unless there is a clear reason.
The safest time to prune walnut trees is from mid-summer to early autumn, while the tree is still in leaf. If you absolutely must, this can be extended into early winter, but avoid pruning in late winter or spring because walnut trees can bleed sap heavily if cut at the wrong time. Choose a dry pruning day with good weather forecast to help cuts dry out. Do not use tree wound sealant, as this can trap pathogens.
For a young walnut tree, keep pruning light. Remove dead, damaged, diseased, crossing or badly placed shoots. If the tree is forming a poor shape, choose a good main leader and well-spaced side branches, then remove competing leaders or awkward branches before they become large.
Some inward-growing young shoots may be trained into a better position rather than cut out. Do not tie string tightly around a walnut branch, as this can restrict growth. Use a loose loop, rubber tree tie or another non-restricting method.
For an established walnut tree, prune only where there is a clear reason. Remove dead wood, crowded or crossing branches, and any low limbs that are in the way. Avoid heavy cutting and do not try to keep the tree small by hacking it back; walnuts respond better to early training and light correction than hard pruning later.
Walnut Tree Shaping For Light And Higher Yields
A walnut tree with a clear main leader and well-spaced side branches is usually easier to train into a strong, open shape. Good spacing helps light and air reach more of the canopy, which supports healthy growth and cropping.
The basic aim is to avoid the upper branches becoming too dominant and shading the lower branches. On young trees, remove or shorten badly placed competing growth early, before it becomes large. Keep the branches well spaced from each other to promote light and air through the canopy.
A bush-shaped walnut tree, where several main branches start low to the ground, is best pruned lightly to keep the centre open and reduce crossing, crowded or inward-growing branches.
Training young side branches to a wider, more horizontal angle can help create a stronger, better-lit branch structure and may improve cropping potential.
