Despite thousands of years of cultivation, the black mulberry (Morus nigra) refuses to hybridise. This means there are no true cultivars or varieties, but any named varieties you come across would be a good choice for an orchard, or as a solitary fruit tree in a garden, provided you have the space.
In contrast, there are dozens, if not hundreds, of cultivars of the white mulberry (Morus alba) and closely related species. Its fruit has been described as ‘insipid’, but unlike the black mulberry, can be dried, easily transported, and used in cooking, where it is sometimes ground into flour.
A few white mulberry cultivars, like ‘Illinois Everbearing’ (a cross between Morus alba and Morus rubra) are juicy, as can be the smaller fruit of Morus alba pendula, the Weeping white mulberry. A dwarf cultivar, ‘Charlotte Russe’, can be grown in a container and fruits from July to October, but it is small and disappointing in terms of taste.
Both female and male catkins occur on the same tree (they are monoecious), but do not need pollination to produce fruit. Unpollinated fruit, though, is seedless, containing ‘empty’ seed cases.
Propagation
I know several people who have simply gathered ripe fruit, washed and sieved the berries, dried the seed and stored it (sometimes with a few weeks in the freezer), and planted it in small pots, before planting out a couple of years later. I had one such two-year-old tree in a container, grown from a seed of a veteran tree, which sadly suffered in the dry heat of 2022. They do need regular watering in the first two-three years and must not dry out.
The traditional technique for propagation is by ‘truncheons’, an arms-length of dormant hardwood cuttings, planted deeply in well-drained soil (about two thirds below ground) during late winter/early spring. This is less successful though than standard hardwood cuttings: prepare pencil-thick stems with three to four buds, dip in rooting hormone, plant in well-drained soil, keep moist, and expect roots in about two months.
Adam Cade, a contributor to the Morus Londinium project, successfully grows black mulberries from cuttings (non-commercially) and offers the following guidance:
- Select some straightish shoots about 20-40 cms long, with at least two buds and no leaves. Mulberry shoots are rarely perfectly straight!
- Cut using secateurs at the top (at an angle above a bud) and bottom (at right angles to avoid confusion with the top!) from one or two year old shoots. Alternatively pull them off as a side branch with a heel. The heel contains auxin (a plant hormone that promotes rooting). Cut a selection of one, two and three-year-old wood.
- Dip the end of the shoot in rooting powder. This is not essential but will help initiate roots.
- The cuttings can be planted in pots indoors, or a long trench in a shallow bed of sharp sand outdoors, with one or two buds above the ground. I make a vermiculite/sharp sand/ sterilised soil 1:1:1 mix for pots.
- By late spring, two or more sprouts should grow.
- Cut the weakest sprouts to leave one strong vertical sprout.
Trees can reach a height of about 12-15 metres, but the canopy spread can easily be wider than this. Black mulberries tend to lean away from shading structures (or nearby tall trees) and can become unbalanced. They may need propping after a few decades. Leaning trees might eventually collapse, but if left alone, can carry on growing and fruiting for centuries lying down, their branches growing skywards as future ‘phoenix’ trees.
Black mulberry saplings are best planted on a lawn with plenty of space around them, with an eye to their future aspect. This also makes it easier to gather the rather messy deep purple, staining fruit when it is ripe in the summer. Some people place a sheet or tarpaulin under the tree to catch the fruit (traditionally encouraged by shaking the branches).
Veteran trees need professional care, though, and if in a public place, may need mulching or a protective barrier to limit footfall, which can lead to compaction, starving the roots of oxygen, nutrients and water, leaving it vulnerable to disease and collapse. Arboriculturist Russell Ball, a consultant on the Morus Londinium project, has produced a useful guide to managing an established mulberry.
Pests and disease
Mulberries are resilient and can endure most of what the British climate throws at them, once established. They are not particularly prone to disease or fungal attack, and the worst that mature trees are likely to encounter is fungal leaf spot (e.g. Cercospora moricola) which is unsightly and usually appears after fruiting. It is rarely fatal.
The spotted-wing Drosophila fruit fly has also become present in Britain in recent years, and can spoil soft skin fruits, including mulberries, and is difficult to eradicate. Traps, timely removal of ripe and dropped fruit, and the use of some sprays can help to limit the fly.
I have seen cases of Ganoderma fungal attack which can eventually prove fatal and spread to other trees, but it is not always a reason to fell the tree, so advice should be taken first.
Mulberries will naturally hollow, with fungus and internal aerial roots aiding the process. But this does not mean the tree is unhealthy or even a particular risk, though it should be regularly inspected. A 350-year-old hollow mulberry in Wanstead recently split, but will probably carry on living for another 300 years with care.
by Peter Coles, author of Mulberry and co-founder of the Morus Londinium project with the Conservation Foundation.