Your Backyard Fruit Bowl – Mulberries

Black mulberry fruit: Image by İsmet Şahina from pixabay.com

O, the mulberry-tree is of trees the queen! Bare long after the rest are green;
But as time steals onwards, while none perceives
Slowly she clothes herself with leaves.
—Dinah Maria Murlock Craik, English novelist and poet

Mulberries are somewhat of an enigmatic fruit, not particularly common in New Zealand, but when they are spoken of, it is usually with great reverence. Apart from the usual childhood brush with the nursery rhyme ‘here we go round the mulberry bush’, I didn’t encounter the fruit until they piqued my interest at university and I went on a mission to seek out the two trees that reputedly grew on campus. Unfortunately, one turned out to be a white mulberry (great if silkworms are your gig) and I’d missed the crop on the black one (plenty of plump birds in the neighbourhood).

Relatively common in Australia, I’m unsure why mulberries haven’t experienced a similar vein of popularity here in New Zealand, as they have a lot going for them. Black mulberries, the most commonly known variety, can be extremely prolific fruiters and have juicy, sweet-tart fruit with a flavour reminiscent of a mixture of blackberries, raspberries and black grapes. Perhaps it’s because they aren’t a commercially viable fruit - the thin-skinned berries are best eaten straight from the tree, their fragility meaning they turn to a pulpy mess when overhandled at peak ripeness and hence it doesn’t take much for mould to set in. Berries eaten straight from the TREE you say? Yes, this curious fruit that looks a little like an elongated blackberry grows on a tree. Yet another advantage over prickly brambles – no tricky thorns to contend with at harvest.

I’ve since found a few black mulberry trees growing here and there and managed to snaffle the odd fruit or two, but they are still few and far between. The Nelson Branch of the New Zealand Tree Crops Association trialled the shahtoot mulberry recently; these mulberries look a little like hairy reddish-purple caterpillars and have proven rather fruitful and capable of providing a bountiful pre-Christmas crop in the Tasman climate. Apart from these, the best finds I’ve had have been in Middle Eastern and other specialist grocery stores, where mulberry jams, syrups and even mulberry molasses abound. In addition to their delicious fruit, mulberries are moderately fast-growing, deciduous trees and make excellent shade or specimen trees when landscaping. I think I’ll start a personal campaign to make mulberries more popular – move over raspberries, it’s mulberries for the masses!

Mulberries: a short family history

Mulberry fruit: Image by Elida Cris Fagundesa from pixabay.com

While mulberries look a bit like black berries and raspberries and belong to the same order as bramble berries (Rosales), they are from a completely different plant family, the Moraceae (mulberry or fig family). Close relatives include figs, tropical breadfruit and jackfruit and the ornamental Osage orange.

There are three main varieties of mulberry:

The black mulberry, Morus nigra is native to western Asia and has been cultivated for many thousands of years, reaching Europe before the Romans and becoming a popular cultivated fruit. It is considered to be the most superior type of mulberry flavour-wise.

The white mulberry, Morus alba is native to eastern and central China and its leaves have been used for centuries to feed silkworms. The fruit is very sweet but lacks the sugar-acid balance that makes black mulberry fruit so palatable.

The red mulberry, Morus rubra is native to the eastern United States from Massachusetts to the southern Gulf Coast states. Flavour wise, the fruit runs a close second to M. nigra. Red mulberries hybridise readily with M. alba.

In addition, the shahtoot mulberry, Morus macrura has a similar physical stature and foliage to M. alba and is native to Tibet, the Himalayas and Southeast Asia but easily distinguished by its long, caterpillar-like fruit (six to eight centimetres in length, sometimes up to 10-12 cm depending on the selection).

The Latin genus epithet ‘Morus’ means delay – lending credibility to the verse quoted in the opening lines of this article and giving rise to another benefit for home growers – flowering after the late frosts in the latter part of spring, fruit set is less likely to be hampered by low temperatures wreaking havoc during flowering.

It’s a well-known fact that many nursery rhymes have dark origins and the perennial favourite ‘Here we go round the mulberry bush’ is no exception. This rhyme is thought to refer to Wakefield Prison in West Yorkshire, referencing the walks around the prison yard that female prisoners interned there would take with their children each day. It’s possible that the mulberry bush referred to is the same one that grew in the prison grounds until 2017, when it succumbed to a beetle infestation and canker. It made the shortlist for the Tree of the Year prize in 2016. Built in 1594, the emblem of the prison remains a mulberry tree. A retired member of staff took cuttings from the original back in the 1980s and it is hoped that a tree propagated from this remnant will be replanted on the grounds.

If silkworms aren’t your thing, mulberry leaves can be brewed into a pleasant brew, antioxidant, vitamin and mineral-rich tea. The wood is durable, resisting rot, and hence useful for making fenceposts. Black mulberry fruits are high in anthocyanins and yield strong pigments which have long been utilised for fabric dyes and as a food colouring.

Suitable climates and growing conditions

White mulberry: Image by Emilian Robert Vicola from pixabay.com

Mulberries are relatively large trees, easily reaching 10 metres at maturity, so allow adequate space (approximately five metres between trees) at planting so the tree can grow and establish itself without being shaded out by neighbours. They require around 400 hours of winter chill to set fruit.

Although there is reasonable variation between cultivars, white mulberries are the most cold-tolerant species (withstanding down to between -3 and -30°C), followed by red (will tolerate moderate sub-zero temperatures) and then black, which will usually tolerate light frosts.

Planting a mulberry is a long-term investment, with elderly M. nigra specimens known to still produce a crop at 200 years of age. M. rubra doesn’t do quite as well in the longevity stakes, but is still able to exceed threescore years and ten.

Mulberry trees are wind pollinated and usually monoecious, with slender male and chunkier female catkins present on the same tree – the good news is you only need one tree to set fruit. A few cultivars are parthenocarpic and able to set fruit without pollination.

Mulberries can start producing fruit within two years of planting, but it will be at least four years before yields are sizeable. Mature trees grown under optimum conditions can produce in the region of 25-40 kg of fruit each. The berries ripen individually, at different intervals, giving a long harvest period over several months, which helps avoid gluts. The fruit freezes well.

Mulberries can be propagated from seed, which is best sown fresh. There are varying opinions regarding the viability of different types of mulberry seed, whether stratification (cold treatment) is necessary for germination, and the need to consider variability from the parent plant as mulberries do not grow true from seed. Seedling trees may take between five and ten years to start fruiting.

Mulberries can be propagated clonally by softwood (in spring), semi-hardwood (in summer) or hardwood (in autumn) cuttings and by layering. Grafting can be somewhat challenging as black mulberries in particular bleed profusely when cut. Budding in spring is reasonably successful, but care must be taken when selecting rootstocks and scions as a degree of incompatibility exists between red, black and white species: they are not always interchangeable for one another.

Site selection and planting

Shahtoot ripening fruit: Image by harishlovemoney from Pixabay.com

Mulberries are deep-rooted, which confers a degree of drought tolerance, and they can also tolerate some wind exposure. Because of this, they suit deep, well-drained soil types - avoid shallow, stony soils. Mulberries will not tolerate extended periods of waterlogging either, so avoid heavy soils and boggy patches. They do best in locations with a full sun aspect and are not shade tolerant.

Because of the mulberry’s extensive root system and sizeable stature, it’s best to keep these stately trees away from house foundations, septic systems and driveways to avoid problems in future. The fruit of black mulberries in particular will stain concrete paths when it drops (think about the location of your washing line when planting, too!).

Culture and care

The mulberry’s deep root system confers a degree of drought resistance, but for heavy crops of plump berries, keep the water up during fruit development, ditto in dry spells to avoid premature fruit drop.
In terms of fertiliser requirements, mulberries are not gross feeders but do best with an adequate supply of nitrogen. Choose a balanced, slow-release general fertiliser and make two applications, one in early spring when new foliage appears, and a second in early summer at fruit set. Water in well after applying. Well-rotted compost or manure can also be applied as a side-dressing or mulch.

Pruning

Young trees should be pruned to establish a basic structure of scaffold branches. Once this is complete, maintenance pruning is minimal. Focus on removing dead, damaged or diseased branches and any that overcrowd or cross over others. Carry out pruning in the winter when the tree is dormant, or if you miss this period, late summer. Avoid spring pruning and large cuts (anything greater than five centimetres in diameter) as mulberries are notoriously heavy sap bleeders and poor healers if not treated with care.

Pests, diseases and what to do about them

Mulberries are a hardy and generally trouble free in terms of pests and diseases. Bacterial blight, canker and branch dieback may occasionally cause issues, but birds helping themselves to your crop will be the biggest problem you’re likely to face. Net your tree well before the fruit starts to turn colour for best results, as even white berries will be stripped from the tree overnight. Keeping your tree pruned to a manageable height will enable you to net it easily.

Varieties: My top picks

The Morus alba x rubra cultivar ‘Hicks Early’ is relatively common and easy to source in New Zealand. There are numerous unnamed black and white varieties in circulation as well. Smaller specialist nurseries may be able to provide other cultivars, including weeping varieties with pendulous fruit, prized for landscaping purposes along with white, red and pink shahtoot mulberries, which bear caterpillar-esque elongated fruit.

What to do with your crop

Mixed mulberry fruit: Image by Анастасия Белоусоваa from pixabay.com

Once you’ve eaten your fill fresh, free-flow freeze excess fruit for winter pies, cakes and crumbles. Substitute for blackberries, raspberries and boysenberries in your favourite cakes and desserts. Mulberry jam is absolutely delicious, but you need to add citrus juice and perhaps some quince or apple pulp to increase the acid/pectin balance respectively.

Black mulberries purportedly dry well on their own, although I haven’t tried this, they and shahtoot mulberries also make an excellent fruit leather when mixed 50:50 with stewed apple. Add a shot of mulberry cordial (sharab el toot) or molasses (pekmez) from a Middle Eastern grocery if you can get it to deepen the flavour. Speaking of the latter, you can make your own!

You could try mulberry curd, mulberry buckle, or mulberry sorbet. If you manage a simply enormous harvest, mulberries are also coveted by home winemakers and make a unique brew.

Disclaimer: the information supplied above is of a general nature and provided as reference material only. In regards to pest and disease control, please consult your agrichemical consultant for suitable products, application rates and further region-specific information.

Anna-Marie Barnes is an active member of the New Zealand Tree Crops Association who endeavours to grow and preserve as much of her own fresh produce as possible. When the weather’s no good for gardening, she can usually be found inside working on a batch of homemade cheese or soap.

The New Zealand Tree Crops Association is a voluntary organisation promoting interest in useful trees, such as those producing fruit, nuts, timber, fuel, wood, stock fodder, bee forage and other productive crops. Find out more about the NZTCA here: https://treecrops.org.nz/

Image Credits:
White mulberry: Image by Emilian Robert Vicola from pixabay.com
Shahtoot ripening fruit: Image by harishlovemoney from Pixabay.com
Mulberry fruit: Image by Elida Cris Fagundesa from pixabay.com
Mixed mulberry fruit: Image by Анастасия Белоусоваa from pixabay.com
Black mulberry fruit: Image by İsmet Şahina from pixabay.com

Planning your orchard? Our Backyard Orchard series can help with advice on most varieties.