hazelnuts

Hazelnuts, the fruit of the hazel tree, are an easy-care addition to the home garden, making them the perfect beginner species if you are new to nut growing. Their distinctive flavour (and affinity for chocolate!) makes them a crowd favourite and their shrubby stature means with a little guidance, they can be encouraged to grow in forms suitable for smaller gardens. They are relatively fast-growing and even make good hedges – perfect for humbugs like me who begrudge garden space for inedible species. There are no messy husks to deal with (looking at you, walnuts) or ridiculously hard shells to crack (ahem, macadamias) and all that is required preharvest is a quick tidy-up underneath the trees (bare earth means easy collection) and a quick pick-up every few days or so when the nuts fall in late summer – autumn.

You may have heard hazelnuts referred to as cobnuts or filberts (particularly in the UK). I’ve often wondered if there is a distinction between these other than at genetic level, and was interested to read recently about the historical context for such classifications. You may have noticed that hazelnuts still on the tree are covered by a frilly green husk, which the nuts fall from when they are brown and mature. The filberts (whose etymological extraction may be from ‘full beard’) have a husk longer than the nut itself. Cobnuts have a husk the same length as the nut, and hazelnuts are species which have a husk shorter than the nut. So, there you have it.

I can’t confess to having a particular connection or amusing family story to tell you about hazelnuts this month, but I did find myself contemplating how to prune two unruly trees in the family orchard recently. It’s just as well I only made some judicious access-only related cuts and then walked away on noticing a bunch of catkins – if you prune in autumn, you risk trimming off the next season’s flowers…and crop. That would have made me wildly unpopular, considering this year’s head count was under ten. I have my work cut out for late winter it seems!

Hazelnuts: a short family history

Hazels belong to the Betulaceae or birch family – you may see morphological similarities between the catkins of birches and hazels – but taxonomists sometimes group them in their own family, the Corylaceae. Of the nine or ten known species in the genus Corylus, just two, Corylus avellana, the European hazelnut (or cobnut), native to western Europe and the United Kingdom and C. maxima (the European filbert), native to southeastern Europe and western Asia, and their resultant hybrids are cultivated commercially. Turkey leads world hazelnut production, followed by Italy and the USA. Turkey has its own native hazel, C. colurna, with the remainder of the species native across North America, China and Japan.

A temperate species, hazels thrive in locales with mild winters, adequate moisture and cool summers. In the Northern Hemisphere, commercial cultivation clusters in the latitudinal strip that runs from the Black Sea to France, with other growing regions including China, the US state of Oregon and good old New Zealand. There is an extremely long association between humans and hazels as a food source; in 1995, evidence of a large-scale Mesolithic nut-processing operation was uncovered on the island of Colonsay in Scotland’s Inner Hebrides. A large shallow pit was found, containing the remains of a few hundred thousand burnt hazelnut shells. It seems this nut was as popular 8,000 years ago as it is today.

When the word hazelnut is mentioned, it is hard to not think of the wonderful marriage between hazelnuts and chocolate which results in the delicious paste known as gianduja (or gianduia) which actually came about in Italy during the reign of Napoleon, when restrictions on the importation of goods such as cocoa caused confectioners to ‘stretch’ chocolate with other more readily available local materials. Hazelnuts were plentiful in the Piedmont region and a chocolatier in Turin decided to experiment – this legacy lives on today in the soft, fudgy to pasty confection composed of roughly 30% hazelnut paste and 70% chocolate that takes many guises as a filling for fancy chocolates to an everyday spread for bread. The Ferrero Group, which manufactures the household brands Nutella (originally called Pasta Gianduja and sold as a solid block) and Ferrero Rocher chocolates currently uses 25% of the world hazelnut crop (global production was 1.1 million tonnes in 2020). The main aroma constituent of hazelnuts is a chemical called filbertone, which is widely used in perfumery.

Hazels also have a longstanding link with mysticism – from the use of forked hazel rods in witches’ rituals, for water divining (dowsing) and the nuts being burned by priests as an aid to clairvoyance. In Celtic mythology, the first creation to grow on earth was a hazel tree, and Ireland’s first hazel tree, which grew upon the Well of Wisdom was said to hold all the knowledge and wisdom of the universe within its branches. Note to romantics: British folklore states that if you court your sweetheart beneath a hazel tree, happiness is assured. Further down the track, take a leaf out of the Romans’ book and burn a hazel torch at your wedding to foster fertility and a happy marriage. Better get planting…

Suitable climates and growing conditions

Although hazels originate from regions where the summer temperatures are comparatively cool and the winters are uniform if not mild, they do have reasonable chilling requirements, approximately 800-1600 hours depending on cultivar. The trees themselves can withstand frosts down to -14°C and the male catkins down to -8°C. It is said that hazels have fairly similar winter chilling and summer growth requirements to apples, so if you can grow a decent crop of apples at yours, it is likely hazels will do well for you too.

Classed as shrubs to small trees, hazels grow on average from around 60 cm high to around five to nine metres at maturity. They are reasonably fast-growing and tend to produce a proliferation of suckers around the base of the tree, handy for propagation purposes but a hindrance when you are trying to develop a neat and tidy canopy structure in the formative years. Individual trees of the taller cultivars can make attractive shade/specimen trees when set in the middle of your lawn. If using as a clipped hedge, bear in mind nuts will be borne on the upper branches only.

At establishment, allow three to six metres between plants, depending on the chosen cultivar and its expected final size. The hazel’s lifespan can easily exceed ours (70+ years) and there are stands which have been subjected to the practice of coppicing which are centuries old. Coppicing is a traditional woodland management technique which involves cutting trees right back to the base (forming a stool, or living stump), then allowing the stump to regenerate new growth shoots – this allows wood to be continually harvested from the tree and in the case of hazels, the new shoots are tall and straight, ideal for garden stakes and fencing. The resultant canopy structure of coppiced hazels is broad and open, allowing the light penetration that is essential for flower formation. As an aside, an area of cultivated hazels was historically known as a plat.

Hazels are monoecious, having both male and female flower structures on the same tree and are wind-pollinated. They are seldom self-fertile, so it is advisable to plant at least two trees to allow cross-pollination. Flowers develop on vigorous one year old wood. The male catkins are conspicuous and develop the previous autumn, opening for a short period in midwinter to early spring (approximately late June to September). The female flowers are very small and easy to miss, forming at or near the ends of stems and consisting of little green bud-like structures with a tuft of bright red stigmas popping out. They open for a period of weeks (much longer than the males) during May and June. As you might have guessed by now, hazelnut pollination is a little unorthodox – and it gets even more complicated. Following pollination, the pollen tubes germinate, but then enter a resting stage until October or November. The actual fruit development phase takes from this point in spring to about March, when the nuts start to ripen – quite a long, drawn-out process.

Ideally, include a polliniser variety which opens and sheds pollen at the same time the female flowers of your main fruiting cultivar open. Commercial block plantations generally include one polliniser for 16-25 trees, or at a rate which totals 10% of the entire planting. Many of the polliniser cultivars available in New Zealand are very vigorous, so prune them hard to keep them from dominating and casting shade on your productive trees.

You can expect a crop four to six years after planting, with trees reaching maturity and full cropping capacity at about ten years of age. Trees will continue cropping well for 40-50 years after this, producing on average 7 kg of nuts each year, with some cultivars capable of producing 13-18 kg each year. Yield is highly dependent on cultivar selection and management practices.

Hazels are propagated by seed (but do not grow true to type and seedlings are usually used only as rootstocks), clonally by grafting known cultivars onto seedling rootstocks (viability can be limited using this method), by layering (reasonably successful) or taking suckers or rooted runners from around the base of the plant. As some of these methods are time-consuming and have limited success rates, unless you are a keen hobbyist propagator, I suggest purchasing plants of the preferred (named) cultivars of your choice from a reputable nursery.

Site selection and planting

You can plant hazels from late autumn till the end of winter (May – August). Choose a sunny, reasonably sheltered location if possible – although as a woodland understorey species, they will tolerate light shading. They suffer in coastal climates and do not handle cold, wet winds in spring when the new foliage is emerging or hot, dry, windy conditions in summer.

Hazels are good-doers in terms of soil type. Medium-textured, deep, well-drained soils are ideal, but most types are tolerated (including clays), but due to their relatively high water requirements, hazels may struggle on sandy soils. Soil pH on the acidic side is ideal; trees may suffer from micronutrient deficiencies in soils above pH 7.

Culture and care

Hazels in their natural habitat thrive growing along stream banks, hinting at their soil moisture requirements. Irrigate regularly throughout the growing season and in particular the nut-fill period (mid-December to March) as hazels are not drought-tolerant.

Hazels are not gross feeders but can be prone to nitrogen, potassium and boron deficiencies. Their fertiliser requirements are similar to stone fruit such as peaches: apply a standard general fertiliser or an organic preparation, allowing 250-500 g per year of age for young trees, up to a total of
5 kg/tree at maturity, aiming for the equivalent of 1 kg N and 0.5 kg K per mature tree each year. Split this in to two or three applications, applied in spring and early summer. Don’t forget to spread this fertiliser before rainfall, or water it in well afterwards.

Pruning

Commercially-grown hazels are usually grown with a single trunk and the canopy (based on a framework of four to five main branches) trained to have an open centre for maximum light penetration – remove inward-growing branches and crossing-over growth. Due to their natural propensity to sucker, unmanaged trees will produce a shrubby thicket-like form, which can be more difficult to access at harvest and result in slightly reduced yields. A hard prune when the tree naturally starts to lose vigour after several years of fruiting can stimulate new, productive growth, but be prepared for a drop in yield the year immediately after. If your trees are prone to biennial bearing (heavy crops one year, followed by a lighter crop the next) you can employ light pruning techniques in years of overabundance to help even out the yield. Aim to prune in late winter, after the male catkins have finished flowering, but make sure you don’t trim off those inconspicuous female flowers at the same time. Flowers arising laterally seem to have better nut-set rates than those borne on at the base of catkins or on spurs.

Wikipedia describes a traditional method of increasing nut production, called brutting, which is carried out at the end of the growing season. This involves encouraging more of the tree’s energy to be diverted into flower bud production by snapping (but not breaking off) the tips of the new season’s shoots six or seven leaf-groups from where they join with the trunk or branch. Worth a try.

Pests, diseases and what to do about them

While hazels are generally pretty hardy, there are a handful of insect pests that affect Corylus spp. in New Zealand. The big bud mite (Phytocoptella avellanae) is a key player and can be controlled with an application of lime sulphur after flowering, but before the leaf buds show ‘green tip’. Remove and incinerate all infested material where possible. New Zealand’s endemic longhorn beetle Oemona hirta, commonly known as the lemon tree borer can cause stem damage (see Your Backyard Fruit Bowl: Beyond the Meyer Lemon for control tips). Aphids and whitefly can also cause issues, often making their presence known by the black sooty mould deposits that form when their populations boom and the resulting feeding frenzy hits fever pitch. An application of a suitable insecticide may be useful in the case of severe infestations, but backyard growers may prefer to release some predatory ladybirds instead.

In terms of diseases, bacterial blight caused by Xanthomonas campestris pv. corylina can develop on the husks and infect the soft, developing shell, later leaving scars on the shells of mature nuts. Copper sprays can assist with control and many modern cultivars have a degree of blight resistance.

Varieties: My top picks

Alexandra – vigorous, late-flowering variety, polliniser for Whiteheart and Merveille de Bollwiller. Heavy crops of well-flavoured nuts, some blight resistance and recommended for cold climates.
Pollen released early, flowers open late.

Whiteheart – the top commercial cultivar in New Zealand. Late flowering, low vigour trees. Large crops of small, round nuts. Susceptible to big bud mite.
Pollen released mid-season, flowers open late.

Barcelona – vigorous cultivar which flowers mid-season. Large, well-flavoured nuts, high yield. Susceptible to bacterial blight. Polliniser is Merveille de Bollwiller.
Pollen released early, flowers open mid-season.

Merveille de Bollwiller – late-flowering, vigorous cultivar, low to moderate yields of large nuts. Polliniser is Alexandra. Ideal for very cold climates.
Pollen (copious amounts) released mid-late season, flowers open late.

Campanica – vigorous, high yielding cultivar producing medium-large nuts with good flavour. Copes with drier climates. Susceptible to big bud mite. Pollinisers include Ennis.
Pollen released early, flowers early.

Tonda di Giffoni – vigorous, high-yielding Italian cultivar, suited to hot dry climates but will not tolerate harsh winters. Medium-sized nuts with good flavour. Pollinisers include Barcelona.
Pollen released mid-season, flowers mid-season.

Ennis – medium-high vigour, high yields of large, sweet, oval-shaped nuts. Recommended as an in-shell nut for the commercial market. Pollinisers include Merveille de Bollwiller and Alexandra.
Pollen released mid-season, flowers late.

What to do with your crop

Gather up your hazelnuts as soon as possible after they drop – don’t leave them on the ground for more than a month after they fall; collect much sooner if the weather is wet, leaf fall coincides with nut fall, or the husks do not detach from the shells. Dry on racks, stirring frequently. In technical terms, bring them down to 10-12% moisture and then bag (use onion sacks or the handy rodent-proof metal cages pictured below) and continue to dry down to 6% moisture. If you use a heated/forced-air drying system, do not exceed 35°C. For long-term storage, aim for a cool, dry room (less than 65% RH and 20°C) and eliminate any strong-smelling products from the vicinity as these can taint the hazelnuts. Unshelled nuts store much better than shelled; cracked nuts should be bagged airtight and frozen.

The hazelnut lends itself to both sweet and savoury incarnations – try your hand at homemade hazelnut butter, an indulgent chocolate-hazelnut spread to rival Nutella, spicy dukkah or festive panforte – Nicola Galloway’s is my favourite version: https://www.stuff.co.nz/life-style/food-wine/recipes/300175311/recipe-hazelnut--fig-panforte

Apple and hazelnut muesli bars

A sustaining, not particularly sweet snack inspired by a long-discontinued commercial breakfast muesli. Makes approximately 24 bars.
Dry ingredients:
2 cups rolled oats
1 cup sunflower seeds
1 ½ cups crispy/puffy cereal: I use a mixture of rice bubbles, corn flakes and puffed quinoa
½ cup thread coconut
½ cup pre-roasted, skinned hazelnuts
½ cup dried apple, diced (scissors make quick work of this job)
1 ½ tbsp hemp seeds

Wet mix:
¼ tsp salt
105 g honey, golden syrup or malt extract
3 tbsp maple syrup
150 g hazelnut butter
30 g butter or coconut oil

Preheat the oven to 150°C and toast all the dry ingredients except the hemp seeds in batches in a large roasting tin, tipping them in a large mixing bowl as each batch is ready. I mix the rolled oats and coconut together and do these first – check and stir every five minutes. Then the cereal if it needs crisping up (this is a good recipe for using up the ends of packets), followed by the sunflower seeds, which will take the longest. If your hazelnuts are raw, roast these after the sunflower seeds and tip them into a clean tea towel, rubbing vigorously to remove the skins. Add the hemp seeds, hazelnuts and apple to the bowl and mix to combine everything.

Grease a 20 x 30 cm Swiss roll pan or 25 cm square pan with oil and set aside.

Combine all the wet mix ingredients in a saucepan over medium heat. Stir well and cook until bubbly and thickened – about five minutes. Keep an eye on it, as the mixture sticks like a devil and burns the minute you turn your back.

Tip the hot mixture into the dry ingredients and mix quickly with a wooden spoon until there are no damp patches. Press the finished mixture into the prepared pan to approximately 3 cm thickness and allow to cool at room temperature (preferably overnight). Slice into bars when cold and store in an airtight container for up to 3-4 weeks. You can wrap individual bars in waxed paper for portability.


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/

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.

Image credits
Young hazelnuts and foliage - Image by Myriams-Fotos via pixabay.com
Shelled hazelnuts - Image by Jacqueline Macou via pixabay.com
In-shell hazelnuts - Image by JolaKalmuk via pixabay.com
Hazelnut drying/storage cages – Robyn Hee