August 2016 | The Garden 6362 The Garden | August 2016

Hybrid berries

TasTe of summerBlackberries scrumped from prickly hedgerows are synonymous with late summer, but cultivated plants can offer better crops, a longer season and spine-free picking, as an RHS Plant Trial revealsAuthor: Jim Arbury, Fruit and Trials Specialist, RHS Garden Wisley. Photography: Tim Sandall

August is usually when our prickly hedgerow brambles begin to tempt passers-by with their succulent, ripening fruit; few people can resist their juicy sweetness. Delicious as the berries may be, wild brambles are

far removed from cultivated and greatly improved blackberries and hybrid berries. Highly productive and ornamental when in fruit, they make a good choice for garden cultivation and are easily trained on walls, fences and arches, as well as being suitable for growing on free-standing posts and wires. Many kinds are thornless and also of greatly reduced vigour, so are more manageable.

Blackberries and their hybridsMembers of the genus Rubus, there are hundreds of species of blackberry including our native brambles (many species, grouped under R. fruticosus) and raspberries (R. idaeus). Cultivated blackberries are usually hybrids – often involving species from overseas – but most are hardy throughout the UK to H6 (−20 to −15�c / −4 to 5�f). Much breeding work has also produced a range of hybrid cane fruits, the current emphasis focusing on black-fruited plants.

One of the first of these popular hybrid berries was Rubus x loganobaccus (loganberry) 7 , raised by Judge James Logan in California in the 1880s from a chance cross between a Pacific coast dewberry and a European red raspberry (probably ‘Red Antwerp’).

Berried treasuresBoxed numbers in the text refer to the following:

1 Blackberry ‘Helen’ 2 Blackberry ‘Ouachita’ 3 Blackberry ‘Navaho’4 Blackberry ‘Reuben’ 5 Blackberry ‘Obsidian’ 6 Blackberry ‘Loch Tay’ agm7 Loganberry8 Blackberry ‘Loch Ness’ agm

✤ Photographed 13 August 2015 at RHS Garden Wisley, Surrey.

A trial of 19 cultivars of blackberry and hybrid berries was planted at RHS Garden Wisley, Surrey in winter 2011/12 and assessed in 2013–15. Entries were evaluated for fruit quality (size, appearance and taste – both fresh and cooked), yield, ease of picking, plant vigour and pest and disease resistance.

Cultivars varied in fruiting season and habit: in 2015 early ones started cropping in July (June in 2014), finishing in August, while later cultivars started in August and cropped until the end of November.

After the trial, blackberry ‘Loch Tay’ earned an Award of Garden Merit (agm) while blackberry ‘Loch Ness’ and Tayberry Group both had agms re-confirmed.

Thorns or thornless?✤ Thornless: blackberry cultivars ‘Asterina’, ‘Cačanska Bestrna’, ‘Chester’, ‘Helen’, ‘Loch Maree’, ‘Loch Ness’, ‘Loch Tay’, ‘Natchez’, ‘Navaho’, ‘Ouachita’ and ‘Triple Crown’. Also loganberry (an unnamed thornless selection) and Tayberry Group ‘Buckingham’.✤ With thorns: blackberry cultivars ‘Black Butte’, ‘Karaka Black’, ‘Obsidian’ and ’Reuben’. Also Tayberry Group and ‘Tummelberry’.

✤ To see the trial report, visit www.rhs.org.uk/planttrials, click on ‘RHS Trials Database’ and search ‘Blackberry’.

RHS Plant Trial of blackberries and hybrid berries

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August 2016 | The Garden 6564 The Garden | August 2016

Hybrid berries

Loganberries are still popular and worth growing today and were included in a recent three-year RHS Plant Trial that ended in 2015. The original tayberry (Rubus Tayberry Group) was produced from a similar cross made at the Scottish Crop Research Institute (now the James Hutton Institute) in the 1970s by Derek Jennings, from black-berry ‘Aurora’ and an improved tetraploid raspberry (with cells having twice as many chromosomes than normal, meaning plants often have more vigour and better crop yields). There are now several selections including thornless tayberry ‘Buckingham’ – although this did not perform well in the trial.

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Blackberries have also undergone great improvements through breeding: there are now many good quality, thornless selections. Early ripening selections have lengthened the season, and cultivated blackberries often have different flavours to wild fruits (although these also vary). Most blackberries and hybrid berries are ‘floricane’ types, producing fruit on laterals from canes produced the previous year; recent breeding has also produced ‘primocane’ types. These (as with primocane or autumn-fruiting raspberries) produce fruit on the current season’s canes, which offers a significant advantage in ease of training as they can be easily supported between parallel wires. The first of these are now available, such as ‘Reuben’ 4 and there will probably be even better cultivars to follow.

Selections to chooseThree selections earned an agm after the RHS Plant Trial:✤ Blackberry ‘Loch Ness’ 8 : a well-known, thornless cultivar of moderate vigour with good flavour if fruit picked when fully ripe (not when it has first turned black).✤ Blackberry ‘Loch Tay’ 6 : one of the best flavoured in the trial with fruit similarly sized to wild blackberries. Of moderate vigour and thornless, it is easy to train and has grown well over an arch at RHS Garden Wisley for years.✤ Tayberry Group: a well-known, early ripening red berry. It has a trailing habit of moderate vigour, has small thorns and is easily trained. Good fresh and cooked.

Other non-agm cultivars worth growing included: ✤ Blackberry ‘Karaka Black’: an early cultivar with long, blunt-ended fruits of excellent flavour. It has thorny canes of low vigour so does not need much space. Although some plants in the trial died, it has grown well on other sites.✤ Blackberry ‘Navaho’ 3 : has thornless, upright canes and large flowers of ornamental value. It crops from late July to November in some years. Fruit size is variable and of good flavour. Some of the cropping is on primocanes. ✤ Blackberry ‘Helen’ 1 : one of the least vigorous, most compact cultivars. Suitable for smaller spaces. ✤ Loganberry 7 : the entry in the trial was a thornless clone and it performed well. It would have been reconfirmed as an agm but the clone name could not be ascertained. It cropped well and is of good flavour, picked fully ripe.

The highest yields in the trial were achieved by blackberry cultivars ‘Asterina’, ‘Cačanska Bestrna’ and ‘Chester’. All are vigorous and fruited in late November at Wisley; much of this fruit will not ripen in cooler areas.

Primocane blackberries are a promising development; ‘Reuben’ had good flavour but needs an early season and a warm autumn to crop well; it does not ripen many fruit most summers. I look forward to growing earlier cropping primocane cultivars in future as they become available.

Hybrid berries can offer heavy crops of luscious fruit from often thornless plants, which usually ripen earlier than wild brambles. Wall- or fence-trained they can make well-behaved, productive and attractive garden plants.

Tayberries produce early crops of red fruit and are quite easily trained on fences or walls.

Blackberries will grow attractively over an arch.

Blackberry ‘Karaka Black’ produces good crops of long, tasty fruit early in the season.

Guide to cultivationSupporting and trainingBlackberries and hybrid berries are best supported on horizontal wires attached to freestanding posts, walls or fences. Use 2.5mm galvanised wire spaced at 30cm (12in) apart, the first wire about 60cm (24in) from the ground, the last at 1.8m (6ft), allowing 2.5–4m (8–13ft) per plant, depending on cultivar. Some have trailing canes, others are more upright; all can be fan-trained (as in the trial).

After planting in winter or early spring, cut canes back to 20cm (8in) to stimulate basal shoots. These develop into new, fruiting canes which can be trained and spaced 15–30cm (6–12in) apart on either side, allowing a gap of 60cm (24in) in the centre, leaving the top wire free for the successive new canes; these are loosely bundled up in the centre and along the top wire until fruiting canes have completed cropping. After fruiting, old canes are removed and new canes tied in 15–30cm (6–12in) apart on either side, as before. Tie these in using soft twine or thin tube tie. Surplus canes are removed at their bases. Where space is limited, training over an arch also works well.

Growing needs✤ Fertile well-drained soil of pH 6.5. Improve drainage on heavy soils and moisture retention on dry soils by digging in well-rotted manure or compost. ✤ Soil should be free of perennial weeds.✤ Shelter from strong winds.✤ Mulch with well-rotted garden compost or manure to help moisture retention.✤ Apply fertiliser annually in spring; use a general fertiliser such as growmore at 70g per sq m (2oz per sq yd).✤ Pests: aphids are often present but not always enough to be a problem and may be controlled by predators. Spray with an approved pesticide if necessary but not when in flower. Raspberry beetle larvae can be found in fruit: if numbers are high, control with a product containing natural pyrethrum. Raspberry leaf and bud mite can cause yellow blotches on leaves and red berry mite can stop fruit ripening. Both were controlled in the trial using predatory mite Ambylesius cucumeris.✤ Diseases: purple blotch, raspberry cane spot and spur blight can be a problem. Good training of canes to allow for air movement, and removal of the old canes after fruiting help minimise problems. Soil-borne diseases verticillium wilt and Phytophthora root rots may occur in soils with poor drainage. ✤ Disorders: magnesium deficiency can show up as interveinal yellowing of the leaves. This can be corrected with foliar sprays of magnesium sulphate (Epsom salts).

Plants will grow on post and wire

supports.

Fan-trained trial plant before pruning.

Pruning and typing in.

Leave the centre clear for new canes.

Tie canes to horizontal wires.

For further information, search ‘Growing blackberries’ at www.rhs.org.uk

RHS website

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