Cobnuts and filberts
Hazelnuts are the fruit of Corylus (hazel) trees and bushes. The most important form are cobnuts (C. avellana) but filberts (C. maxima) are also grown. These sweet nuts have been in cultivation for centuries and make a tasty addition to any orchard or large garden.
Botanical name Corylus avellana, C. maxima
Flowering time Early spring
Planting time Plant in dormant season
Height and spread Will reach 6m (20ft) by 5m (15ft) if unpruned
Aspect Sheltered, full sun, well-drained soil
Hardiness Fully hardy (really low temperatures can affect cropping)
The difference between cobnuts and filberts
The cobnut has a short husk (papery casing to the nut) from which the nut protrudes, whereas the husk of the filbert is long and covers the nut.
Growing cobnuts and filberts
- Cobnuts and filberts crop best when they are grown in full sun or light shade
- They prefer a sheltered position with no frost pockets. Cobnuts are the least hardy, so cropping may be affected by winter temperatures falling below -10°C (13°F) as this disrupts pollination
- Cobnuts and filberts are monoecious, bearing separated male (catkins) and female flowers on the same tree. Hazels (cobnuts and filberts) are wind pollinated and crop more reliably when grown in groups. It also helps to plant them in a square formation to maximise pollination
- Better pollination is obtained if two or more cultivars are planted
- They will tolerate many different soil types but prefer light, sandy, well-drained soils with a pH of 6.5-7.5. Fertile soils can lead to excessive growth, making them harder to manage, with poorer crop levels
- Apply a yearly feed of a balanced fertiliser such as Growmore (70g per sq m or 2oz per sq yd) in late winter. Mulching around young trees helps retain moisture during those first few years. Water during dry spells in spring and summer
- Plant between November and March, when the tree is dormant
Pruning and training
Pruning new plants
Cobnuts and filberts grow on their own roots so you do not need to worry about rootstock selection. They are usually bought in as one year old whips which are straight up and down with no branches.
- Prune the leader to the height of 45cm (18in) in the winter after it has been planted
- The following summer it will produce laterals (sideshoots). Remove any shoots growing low down on the main stem and any other laterals that are badly placed. Well-placed laterals should be shortened by a third
- The following winter, remove any excessively strong, upright growth. To create a well-balanced framework, tip prune the sideshoots
- The shape you are aiming for should be open centred with no more than eight to ten leaders growing upwards and outwards
- Stop (remove the tip of) the main laterals when they reach a height of 1.8-2.1m (6-7ft), cutting them back to a bud or weak lateral. This will encourage sideshoots which will bear the catkins and flowers
Pruning established plants
Summer pruning: In August you can use a technique called "brutting" to get established bushes to crop more heavily. By hand, break the longer side-shoots of this season's growth by bending in half but leave the broken section hanging on. This opens up the bush and lets in the light to encourage more female flowers to form on the weaker growth. It also reduces vigour.
Winter pruning: Winter pruning is undertaken to remedy congested growth. The ideal time to winter prune cobnuts and filberts is when the catkins are releasing their pollen. The disturbance will release more pollen and increase the rate of pollination.
- Shorten the brutted branches from the summer to three or four buds
- Leave the short twiggy weak growth alone as this mainly carries the female flowers
- On mature bushes remove up to a third of old or overcrowded shoots. Cut them right back leaving only a 2.5cm (1in) stub; new branches will re-grow from this point
- Keep the centre open and free of inward-growing shoots
- Remove any suckers from the base of the tree
Harvesting and storage
Cobnuts and filberts should start to produce nuts after three or four years. They should be harvested when the husks begin to turn yellow around late September.
Store the nuts in a dry, airy room or shed in slatted boxes in shallow layers or in net bags hung up. They need to be turned regularly to ensure they are drying evenly. Once they are dry remove the husks and store as before.
If squirrels are a problem, you may need to harvest your crop before they have ripened; however, they will not develop such a good flavour.
- Cut the parent plant back to ground level and allow it to resprout
- Between spring and midsummer, gradually cover the base of the new sprouts with a mound of soil, allowing the shoots to root in the dark beneath the soil
- The following winter, sever the shoots from the parent and plant in a nursery bed
- After 2-3 years the plants should be big enough to be moved to their final position
Although cobnuts and filberts can be propagated from seed the plants are likely to be markedly inferior to the parent plants. The seeds need cold stratification as explained in our advice page Trees and shrubs from seed.
Commercial producers may graft plants often using the whip graft method.
Corylus avellana ‘Cosford’: self-fertile good pollinator, produces sweet nuts with a thin shell, reliable.
C. avellana ‘Pearson’s Prolific’ (syn. ‘Nottingham Prolific’): a self-fertile small tree, a good pollinator.
C. avellana ‘Red majestic’ (PBR) AGM: a compact small tree with dark purple leaves and purplish-pink catkins.
Corylus maxima ‘Kentish Cob’ (syn ‘Lambert’s Filbert’): Self-fertile ,good flavour and fine textured nut. Hardy and reliable.
C. maxima ‘Gunslebert’: Heavy cropping with medium-sized nuts of strong flavour.
C. maxima ‘Red Filbert’ AGM: Notable for its burgundy to purple spring foliage, purple catkins and red nuts.
Aphids can be a problem in the spring when the foliage is soft and lush.
You need to keep a close eye on the local population of squirrels as they could devastate your crop.
With the stored nuts mice can become a problem so protection may be needed.
Nut weevils are the cause of many nuts, especially filberts, found with small holes, or in later summer maggots, within the nuts. There is no remedy but to cultivate the ground beneath the bushes in winter to destroy some of the overwintering grubs.
The large leaves of hazelnuts can be prone to powdery mildew especially in a dry season and if there is a lack of air circulation in overcrowded bushes.
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