Blackberry and Raspberry – Rubus spp.
BLACKBERRY AND RASPBERRY TAXONOMY
Blackberries and Raspberries, often termed “Brambles“, are a diverse group of species and hybrids in the genus Rubus. They are members of the Rosaceae family, closely related to strawberry in the subfamily Rosoideae. Rubus is one of the most diverse genera of flowering plants in the world, consisting of 12 subgenera, some with hundreds of species.
Three species with greatest horticultural importance are recognized as:
Blackberry – “Rubus spp.” is the best approximation to a scientific name, considering that blackberry may be the most taxonomically complex of any fruit crop. R. ursinus Cham. & Schlect. is native to the Pacific Northwest, and has been useful in producing commercial cultivars grown in that region. In Europe, there are 6 species in the Moriferi section that have been used to produce cultivars of local importance; they are referred to as the aggregate species R. fruticosus L. agg.
Red Raspberry – R. idaeus L. The European subspecies of this group is designated R. idaeus subsp. vulgatus Arrhen., whereas the North American red raspberry is termed R. idaeus subsp. strigosus Michx., or more simply R. idaeus (European) and R. strigosus (North American).
Black Raspberry – R. occidentalis L. This is fairly straight-forward, being a good species of its own. Its range overlaps that of R. strigosus, but extends further to the south.
The distinction between blackberries and raspberries revolves around fruit characteristics. All bramble fruits are aggregate fruits, which means they are formed by the aggregation of several smaller fruits, called drupelets. The drupelets are all attached to a structure called the receptacle, which is the fibrous central core of the fruit. In raspberries, the receptacle remains with the plant when fruit are picked, creating the hollow appearance of the harvested fruit. In blackberry, the drupelets remain attached to the receptacle, which comes off with the fruit when picked. A second distinction – raspberry drupelets are hairy and adhere to one-another, whereas blackberry drupelets are hairless and smooth.
Some of the most important commercially grown brambles are actually blackberry – red raspberry hybrids. Examples include ‘Boysenberry’, ‘Loganberry’, and ‘Youngberry’. The fruit flavor is unique, but culture and management is more like blackberry than raspberry. Major Rubus hybrids include:
Blackberries. Cultivars are classified by growth habit – trailing, erect, semi-erect, and also as thorny or thornless. In the Pacific Northwest, trailing types comprise 98% of acreage, like ‘Thornless Evergreen’, ‘Marion’, and ‘Kotata’. Marion is 50% of the acreage; growers in Oregon call them “Marionberries”, not blackberries. ‘Thornless Evergreen’ is a spine-free mutant of the European species R. laciniatus.
Red Raspberries. As with blackberry, cultivars are distinguished by growth habit, trailing or erect. Primocane or autumn fruiting raspberries are a unique group that can produce fruit in their first year, or two crops per year (see below). ‘Heritage’, ‘Amity’, ‘Redwing’, and ‘Autumn Bliss’ are major primocane fruiting types. In the Pacific Northwest, ‘Meeker’ is grown on about 60% of the acreage, ‘Willamette’ on 30%, and a few others are grown on the remaining 10%.
Black Raspberries. Few cultivars of this species are grown. ‘Munger’ is grown on >90% of the acreage in Oregon, and ‘Allen’, ‘Blackhawk’, ‘Bristol’, and ‘Jewel’ are available for home garden culture.
ORIGIN OF RUBUS, HISTORY OF CULTIVATION
Blackberry. Blackberries are native to Asia, Europe, North and South America. However, blackberries grown in specific regions are largely derived from species indigenous to that region. Blackberries have been used in Europe for over 2000 years, for eating, medicinal purposes, and as hedges to keep out marauders. In the US, R. allegheniensis, R. argutus, R. cuneifolius, and R. canadensis have been important in developing “northern” blackberry cultivars, including thornless types (cultivars popular in the western US also). In the southeastern US, R. trivialis has been used to confer low-chilling and disease resistance into cultivars, such as ‘Brazos’. In Europe, R. lacinatus (“cut leaf” or “evergreen”) was the first domesticated species; it was imported into the Pacific Northwest in 1860, where it produced one of the main cultivars for that region, ‘Thornless Evergreen’. R. ursinus is native to the Pacific Northwest and has been important in the development of trailing cultivars grown in that region.
Red Raspberry. The species is indigenous to Asia Minor and North America, (see above) although the epithet denotes Mt. Ida, in the Caucasus mountains of Asia Minor. Fruits were gathered from the wild by the people of Troy and the foothills of Mt. Ida around the time of Christ. Records of domestication were found in 4th century writings of Palladius, a Roman agriculturist, and seeds have been discovered at Roman forts in Britain. Hence, the Romans probably spread cultivation throughout Europe. The British popularized and improved raspberries throughout the middle ages, and exported the plants to New York by 1771.
Black Raspberry. This species is indigenous only to North America, where it is most abundant in the east, exclusive of the Gulf states, and found in the west along with related R. leucodermis. Domestication appears to have been delayed until the 1800s, due to the popularity of red raspberries and abundant supply of wild fruit. In 1850, H.H. Doolittle discovered tip layerage as an efficient propagation method, and released ‘Doolittle’. A rival of his released ‘Doomore’ shortly thereafter, but both were superseded by ‘Ohio Everbearer’. By 1880, there were at least 17 named cultivars, and several thousand acres under cultivation in New York. Today, black raspberries are the least important of the brambles, with very little commercial production compared to blackberries or red raspberries. They make fine garden plants in the mid-Atlantic region of the eastern US, the Midwest, and Pacific Northwest.
WORLD AND UNITED STATES BLACKBERRY AND RASPBERRY PRODUCTION
For the most up to date statistical data on United States and World production numbers please refer to the following two websites:
World: The Food and Agriculture Organization of the United Nations Statistics Division (FAOSTAT). FAOSTAT
United States: The United States Department of Agriculture National Agricultural Statistics Service (USDA Ag Stats). USDA Ag Stats
Blackberries and raspberries are erect, semi-erect, or trailing, generally thorny shrubs, producing renewal shoots from the ground called “canes”. The plants are perennial, composed of biennial canes which overlap in age. Individual canes grow vegetatively for one year, initiate flower buds in late summer, fruit the following summer, then die. The first year canes are called “primocanes”, and in the second year when they flower, “floricanes”. Raspberry thorns are finer and more flexible than thorns on blackberries. Within raspberries, black and purple have more prominent thorns than red raspberries. Leaves are palmately compound with 3-5 leaflets, the middle one being the largest. Leaf margins are finely serrate.
Red raspberries are unique in that there are some primocane (syn. Autumn fruiting) cultivars available which produce fruit in their first summer, and allow the crop to be treated more-or-less as an annual.
White to pink flowers (1″ diameter) are borne terminally on several-flowered racemes, cymes, or corymbose inflorescences on current season’s growth. For dewberry, raspberries, and some wild blackberries, inflorescences are cymose, and some flowers are borne singly in axils of leaves on fruiting laterals. Blackberry flowers generally have larger petals than those of raspberries. Flowers are initiated in late summer in biennial types, early to mid-summer in primocane fruiting types. The gynoecium consists of 60-100 ovaries, each of which develops into a drupelet. There are 60-90 stamens, five sepals and five petals.
Most cultivars of blackberries, black raspberries, and raspberries are self-fruitful and do not require pollinizers. However, dewberries are self-incompatible, and must be inter-planted for good fruit set. Honey bees are naturally attracted to brambles, and wind also aids pollination.
In all brambles, the fruit is an aggregate of drupelets. Blackberries retain the receptacle within the fruit at harvest. Fruiting begins in the second year of the planting, and continues for >10 years if properly managed. Fruit development occurs rapidly, taking only 30-50 days for most raspberries, and 40-70 days for blackberries.
Soils and Climate
Brambles are suited to a wide range of soil types, from sandy to clay loams, provided with good drainage and pH of 5-7. Depth is not important since plants develop shallow root systems, although blackberries are more deeply rooted and therefore drought tolerant than raspberries as a rule.
Soils previously planted to solanaceous crops (pepper, tomato, eggplant, potato) in the last 5 years should be avoided, since a fungus that can kill raspberry roots is harbored by these plants.
Climatically, blackberries have a more warm-temperate adaptation than do raspberries. Black and red raspberries generally require cooler summers than blackberries, and are poorly adapted to the southern USA or to hot, arid climates. Mid-winter cold hardiness can be a great limitation in growing blackberries in the northern USA or away from the moderate, maritime climates of Oregon and Washington. Tender cultivars can be killed at 0 to +10 F, and the hardiest tolerate only about -10 F. Raspberries are more cold hardy than blackberries, with red hardier than black or purple raspberry. Red raspberry can tolerate -20°F, whereas black and purple raspberries are injured at -5 to -10°F. Frost damage is generally not a problem for brambles. Blackberries generally have lower chilling requirements to break dormancy than raspberries, ranging from 200-800 hr. Raspberries have chilling requirements ranging from 800-1600 hr.
Unlike many fruit crops, brambles are easily propagated by a number of techniques. In fact, most propagate themselves quite well, and can be invasive or even weedy.
Root Cuttings. Roots about pencil-size are cut into pieces 4-6 inches long and planted 2-3 inches deep, 1-2 ft apart in rows. Root cuttings are dug in Jan – Feb., and planted in Mar-April. There are notable exceptions to root cutting propagation. Trailing blackberries, as well as black and purple raspberries, do not produce adventitious buds on roots, (or do not produce enough) and cannot be propagated this way. They are tip-layered. Thornless mutants of trailing cultivars (‘Thornless Evergreen’, ‘Thornless Logan’, and ‘Thornless Youngberry’) are periclinal chimeras, and will produce thorny shoots if propagated by root cuttings.
Suckering. Basically the same as root cuttings, except the adventitious buds have already produced canes.
Tip Layering. This is used for black raspberries, hybrids, trailing types, and thornless mutants in lieu of root cuttings. In late summer, when canes have numerous shoot tips, shoot tips are buried in shallow holes. Lateral roots form on stems, and the following spring, layered plants can be dug and transplanted.
Leafy Stem Cuttings. This method can be used for any bramble; semi-hardwood cuttings are rooted under mist in mid-summer.
Tissue Culture. This is used to a limited extent, especially when virus-free material is difficult to obtain by other means.
Rootstocks – None
Planting Design, Training, Pruning
Most erect-growing Rubus are grown in hedgerows, spaced 8-16 ft apart (commonly 12 ft) to allow for equipment movement. Hedges are kept to heights of 4-6 ft, widths of 30 inches on top, with canes arising from a 12″ strip down the row to facilitate mechanical harvesting equipment. Trailing types must be trained on a trellis, usually 2 or 3 wires spaced 18 inches apart, with the top at 5-6 ft. Primocanes are trained by spiralling them around the wires, spacing them as evenly as possible. Alternatively, they may be bundled and tied to the trellis at regular intervals.
Alternate year production is one method of simplifying bramble training. Canes are mowed to the ground every-other year, and produce a crop in alternate years. Costs of production are substantially reduced.
Primocane raspberry culture – As mentioned above, primocane or “Autumn fruiting” raspberries produce fruit terminally on current season’s canes. This allows growers to prune all canes to the ground each year without a yield penalty, greatly reducing disease and insect problems, and simplifying cultural practices. All that is needed is a simple support system, as canes top-heavy with fruit tend to bend over.
For erect cultivars that are not mowed for alternate year production, three main pruning practices are required each year: 1) topping, 2) dead floricane removal, and 3) primocane thinning. The basic pruning needsof trailing and some semi-erect cultivars differ only in the lack of need for cane topping. Primocanes can be shortened to 6-8′ during the winter when floricane removal and cane thinning are practiced.
BLACKBERRY AND RASPBERRY HARVEST, POSTHARVEST HANDLING
Berries are mature when they have completely developed their characteristic color, and are easily detached from the plant.
See pictures –
Postharvest Handling, Storage.
Brambles are extremely perishable, lasting only 2-3 days at temperatures of 32-45°F. They are also easily crushed, and must be picked into shallow flats – typically 12-pint flats that can be marketed directly without further handling, or ½ or 1-pint plastic “clamshell” containers.
BLACKBERRY AND RASPBERRY CONTRIBUTION TO DIET
Almost all brambles are processed; perhaps 10% of the crop is sold fresh. Among the products using bramble fruit (in order of importance): preserves, jam, jelly; bakery products; frozen fruit; juices, extracts; ice cream, yogurt ; canned. Per capita consumption is 0.08 lb/yr for blackberry, and 0.22 lb/yr for raspberries.
Nutritional value per 100 gram edible portion:
|Raspberry & Blackberry|
|Crude Fiber (%)||< 1|
|% of US RDA*|
* Percent of recommended daily allowance set by FDA, assuming a 154 lb male adult, 2700 calories per day.