Northern Viticulture
Reviews and studies
© Juha Karvonen
Photographs: Juha Karvonen
Cover photographs: Pertti Harstela and Juha Karvonen
Cover design: Ida Tokola
Layout: Juvenes Print – Suomen Yliopistopaino Oy
Publisher: BoD – Books on Demand GmbH, Helsinki, Finland
Manufacturer: BoD – Books on Demand GmbH, Norderstedt, Germany
ISBN: 978-952-330-858-9
To my grandfathers
My idea to experiment with wine-growing at high latitudes in Northern Europe came to me while I was a visiting researcher at the University of McMaster in Ontario, Canada. Near the University, 40 kilometers north of Niagara Falls, were about 20 vineyards established by European immigrants which produced, in my opinion, quite good wine from Vitis vinifera L. varieties in circumstances corresponding to those of Southern Scandinavia.
At the end of my carrier, I began studying wine growing at Napa Valley College, in California and continued my viticulture studies at the University of Applied Sciences Eisenstadt, Austria. Later, I received my MSc (horticulture) from the University of Helsinki. On the basis of my studies and experiments I have also written following books in Finnish: Arktisen viininkasvatuksen oppaan (Guidebook to Arctic wine growing) and Viiniköynnöksen kasvatus Suomessa (Viticulture in Finland).
I have also written Northern viticulture based on my own 25 years of experiments and research on viticulture in the southern regions of Northern Europe and the Baltic Sea region at 55 – 60°N latitude. The book deals with the suitability of the current climate as well as circumstances and conditions of these regions for viticulture and how predicted change in the climate should facilitate it.
I express my deep gratitude for invaluable contribution to Mr Jaan Kivistik, at Räpina Aianduskool, Räpina, Estonia; Mr Lars Hagerman, at Domain Aalsgaard, Denmark; Mr Edgars Zihmanis, at Vīnogu Dārzs,Tervetes pagasts, Latvia; Mrs Lena Jörgensen and Mr Murat Sofrakis, at Vingården i Klagshamn, Klagshamn, Sweden, Mrs Helena Tiililä and Mr Raimo Saar, at Tiililä Farm, Pälkäne, Finland, meteorologist Asko Hutila, at Finnish Meteorological Institute, Helsinki, Finland, and secondary school lecturer Pekka Karvonen, Vehmersalmi, Finland.
I have received valuable technical assistance from Mr Mikko Niemi of Ekoweb in Turku, Finland, and from MSc Jyrki Ollikainen at the School of Information Sciences, University of Tampere, Finland, as well as invaluable scientific support from PhD Riitta Törrönen, University of Eastern Finland, Kuopio, Finland, and Prof. ing. Pavel Paulovšek, at Mendel University in Brno, Czech Republic.
Above all, I thank my wife Anna-Liisa for her assistance and everything else.
Juha Karvonen
Tampere, Finland, April 2016
The history of the European grapevine (Vitis vinifera L.) originates in the Fertile Crescent along the Euphrates and Tigris rivers some 10,000 to 12,000 years ago. From there the vine has found its way, through Egypt and Greece, to the Mediterranean countries and, through the Roman Empire, to Central Europe. The Greeks used wine both a drink and a mercantile product, but the Romans used it for their expansion policy also. The present European borders of viticulture roughly follow the borders of the Roman Empire and Charlemagne's (768 – 814) empire.
Viticulture nearly vanished in Europe during the Migration Period. During Charlemagne's reign it recovered and retuned rapidly to its former regions. Charlemagne favoured viticulture and passed laws promoting it. At this time, Nordic inhabitants became more familiar with wine. Then they made lively fur trade with the Franks and Frisians. At that time, the Nordic countries dominated European fur trade, which tempted Central European immigrants northward. These immigrants brought with them knowledge of viticulture and wine making.
Wine had attracted northern people ever since they learned to know it through their trade, expeditions and military campaigns to the south and west. Wine made from grapes has always been an imports in Northern Europe. Vikings made honey wine, whose manufacturing method has survived until our time. The earliest findings related to grapes discovered in Southern Finland date back to the 4th century AD. These included grape seeds probably not from grapes grown in Finland, but from dried grapes sold by foreign merchants.
We have mainly the Romans to thank for Central European viticulture, which reached 51°N latitude (Cologne, Freyburg, Saale-Unsrut) in Continental Europe, and even 55°N latitude in Britain, the same latitude as Copenhagen. Thus far, 50°N latitude has been considered the northernmost boundary for viticulture, which, as a result of global warming, has begun to migrate towards the north and north-east.
The Baltic Sea region (54 – 57°N), south of the Baltic Sea, had viticulture during the warm medieval period of the 14th century (Gladstones, 2011). In the protection of European monasteries viticulture spread to Denmark in the 15th century, but the climate cooling during the Little Ice Age in the 16th century almost completely snuffed it out. Estimates (Stocker et al., 2013) indicted that the temperature of the northern hemisphere reached its lowest in the 16th century, when it was on average – 0.65°C lower than the annual mean temperature of 1881 – 1980.
A grave monument depicting wine transport in Augsburg (48°N; 10°E) from 200-230 AD.
Remnants of northern medieval vineyards are still visible in the Latvian town of Sabile, where viticulture began in the 15th century, survived through the cold period of the 16th century, and revived during the brief warming of the 1930s – so much so that the period even saw overproduction (Zihmanis, 2011, personal communication). However, Word War II and the communist regime ruined it almost entirely. In England, the vine was cultivated in the 11th and 13th centuries, but there, too, climate cooling and the Puritan regime put an end to it for centuries.
Medieval viticulture did not extend to Finland, Sweden and Norway, but greenhouses of the manors of southwest Finland and Southern Sweden in the18th century did grow vines imported from Central Europe and the Baltic countries. Grapes were used not for wine making, but simply to eat during parties. Greenhouse viticulture practiced by the gentry spread even to Northern Savonia province in the beginning of the 19th and 20th centuries (Ollikainen, 2010, personal communication). At the same time, the first experiments with wine growing on open land began in Southern Finland, where reports of vine pests soon followed (Reuter, 1914).
Professor Olavi Meurman began open land viticulture experiments in the 1920s and continued them into the 1950s. He also published several research papers and reviews. Meurman used North American Vitis riparia L. and Vitis labrusca L. varieties, both of which tolerated frost and returned a good yield in southwest Finland. However, due to their long ripening period they did not yield fruit on open land in central Finland.
The warming of the Nordic climate, which began more than a century ago, will continue further as a consequence of the greenhouse effect (IPCC, 2001; 2007; 2013) and likely shift the professional viticulture and wine making northward up to 60°N in 2041 – 2070. Denmark, Poland and Northern Germany would be the new wine production areas. Respectively, conditions for viticulture in Southern Europe (e.g. the southern parts of the Iberian Peninsula), will deteriorate owing to heat and decreasing precipitation (Fraga, 2014). Current wine production areas will see less frequent rainfalls, but in greater quantities at a time, which will lead to flooding.
Precautions should be taken by breeding plant species and varieties, which require less water and are more heat resistant. Excessive heat turns the red wine grapes pale and decreases their anthocyanin and flavonoid content. Furthermore, heat impairs the quality of red wines. All of this would change the temperature-based classification of current wine production areas or new cool regions would have their own classification (Santos et al., 2002; Fraga, 2014).
A vineyard in Sabile, Latvia, dating from the 16th century, uses terraced growing of a vine variety known in Latvia as autochtonous 'Zilga'.
At present, Central and Southern Europe vine varieties do not necessarily thrive in northern latitudes despite global warming. The Central and Western European varieties cultivated in the currently marginal growing conditions in Northern Europe seem to have the best prospects. Securing the production of high-quality wine will require the breeding of vine varieties resistant to plant diseases and pests and suitable for cultivation in the north in good time. They could give Nordic wine unique character, which differs from that of other more traditional European wines.
Late and early frosts are problems for wine growers everywhere, and they determine the choice of vine varieties. Even though the end of April may be warm in the Baltic region, and vines typically begin to awaken from their dormancy and their first buds open, severe frosts (-5°C) can sometimes occur in the middle and in even towards the end of May. If the vines have begun to sprout new summer shoots, they are in danger of freezing, especially if they are uncovered. Even so, this is no reason to fret. Vines have reserve buds, which develop new shoots, once the weather has finally warmed up. However, this stresses the vines and delays flowering, so the vintage does not have time enough to ripen before the early frost. Similarly, delayed flowering also delays the dormancy of shoots, and winter resistance suffers.
Due to weather conditions and sudden temperature changes in spring, vine varieties suitable for northern conditions should not sprout and flower too early. Therefore, vine varieties suitable for 60°N latitude should not sprout before early-May, and flower before mid-June. Then the grapes will reach their normal size in August and begin to ripen in the first half of September. By late-September they will be ready for picking. Even in the southern parts of the Nordic countries the grapes of vine varieties should ripen within ten to twelve weeks after flowering.
The first autumn frosts in the Baltic Sea region occur at the end of September, but the growing season can last an additional month or so thereafter. This gives the vines time to strengthen and ripen before winter. If the vine varieties are traditional, slowly ripening varieties from Southern Europe, the leaves and shoots remain green with high water content and can freeze. If the bark color of the shoots has no reddish or brownish color changes, the vine is not ready for dormancy. Thus, the vine´s capacity for wintering weakens decisively, and the vine may suffer frostbite and damage during a strong winter.
The flowering of several European red wine vines is sensitive to late frost. The grapes of old Central and Southern European varieties ripen, from flowering to harvest, in approximately one hundred days (i.e., three and half months). That is why dark grapes, which flower early and ripen late, are cultivated mainly in Southern Europe. Owing to breeding and crossing, the boundary of red wine production has extended recently to the more northern regions.
Austria which belongs to the EU's northern viticulture zone A (Finland, Sweden, and Denmark belong to this same zone), has cultivated mainly white wine varieties. Nowadays, however, Austria grows more red wine than white wine varieties. Crossing frost-sensitive European Vitis vinifera L. varieties with the frost-resistant Asiatic Vitis amurensis Rupr.varieties and North American vine varieties has improved the frost and winter resistance of European vine varieties.
In the Northern German wine regions and in Hungary, the weather in spring finally warms up only about two or three weeks before it does in Southern Finland. In Germany night frost can occur even in the beginning of May, so, although the differences are rather small in spring, they become more apparent in autumn. The German and Hungarian autumn, where the daily temperatures may exceed 20 °C (though still with the possibility of a slight night frost), is longer and warmer than the Scandinavian one. In the course of the long and warm autumn, the grapes can ripen in peace. In the north, however, the weather can suddenly turn frosty or daily temperature differences may be great.
Once, when vines are selected for the Nordic growing experiments on open land, attention should not be focused only on their frost resistance, but also on their ripening speed. Many vine varieties survive winter in open land easily, but they fail to ripen the grapes sufficiently before winter. Garden stores still sell old Frankenthaler (Black Hamburger) and Foch varieties, leftovers from earlier trial period. In northern viticulture, these varieties for open land growing ripen only in mid-October or later, which in Nordic countries excessively predisposes them to frost.
In Northern Europe, viticulture is restricted by growing seasons that are shorter than those in Central or Southern Europe and the Mediterranean climate. Along with the predicted climate warming in Northern Europe, the soil temperature will also rise, the growing season will extend, winters will become milder and the snow cover reflecting the sunshine back will reduce in the spring.
At high latitudes, solar radiation would be sufficient for the photosynthesis of plants already in March, but the snow cover reflects a large share of it back, so the radiation cannot warm the soil. If the snow cover disappeared early in the spring, solar radiation would be absorbed in the soil, raise the soil temperature earlier than currently, and the growing season would become longer, but at the same time, the protection of the snow cover during cold spells would be lost.
In the winter, the soil and snow layer protect the roots of grapevines and the base from frost. Therefore, it is of utmost importance to find the correct planting depth. The roots of a vine planted deep below the frost limit remain intact, if the soil temperature there remains above 0 °C even in cold and snowless winters. On the other hand, it must be kept in mind that the deeper the vine is planted, the slower the soil temperature rises after winter. It will delay the beginning of the grapevine’s weeping and growth, and the ripening of the crop.
A study straddled the temperatures of the ground surface and soil 60 – 63°N and tried to deduce from them what would be safe planting depth at these latitudes. The temperature measurements were first taken at the ground surface. When the lowest temperature of the ground surface was -16.9 °C and the snow cover was 20 cm, the temperature of the surface soil was – 0.7 °C at the depth of 20 cm. Then, a planting depth of 20 cm is not enough at these latitudes, because the roots of a vine planted at such a shallow depth may freeze at very low frost temperatures.
Although the surface soil and even a thin snow cover on it act as fairly decent insulation during winter, it will not protect the roots of a grapevine at 20 degrees of frost. At a depth of 60 cm, the subsoil temperature remains at +2 °C, even at the lowest sub-zero outdoor temperature. Based on this and later measurements, it has been deduced that in Southern Finland, as well as in all of Central and Northern Europe in general, a planting depth of 40 – 60 cm is safe enough to grow grapevines in mineral soil.
The correlation between the air and soil temperatures (°C) at a depth of 60 cm in 2007. Vertical axis is the soil temperature and horizontal axis air temperature.
In Finland, the coldness of the winters and the thickness of snow cover vary from year to year. In Southern Finland, the thickness of the snow cover varies between 20 and 80 cm, depending on the winter. Even in mild winters, the snow cover of the ground surface is thin and may stay on the ground only for a few weeks, melting away in between. It is generally thought that snow cover prevents viticulture up north. However, snow is not a foe, but a friend to a northern winegrower, because a thick snow cover efficiently protects the lower parts of a grapevine’s stem and roots from frost, and the colder the winter, the thicker the snow cover.
Winter hardiness depends on several factors such as resistance to frost, freezing and flooding and resistance to various plant diseases. Oxidative stress due to lack of oxygen is common to these factors. The stress leads to weaker growing power of plant cells and the plant, and lower stress tolerances. This vicious circle may gradually result in the plant dying. Toxic chemicals used to protect against plant diseases over a long period may also cause oxidative stress (Smallwood et al., 1999).
In Quebec, Canada, Siberia and other areas with severe winters, where the temperature there may be as low as -40°C, grapevines survive the winter primarily because of the thick layer of snow. To increase the snow layer, snow fences, which collect snow driven by the wind into snow layers of many metres thick, are built in the middle of a vineyard. In the upcoming decades, viticulture in such areas may begin to suffer from lack of snow, because due to global warming, the snow cover will also decrease, but cold spells will still occur (Cahilll and Field, 2008).
The colder the winter – the thicker the snow cover
Viticulture in Quebec is a good example, demonstrating that severe sub-zero temperatures lasting for months will not prevent viticulture if the snow cover is sufficiently thick in winter, and that nature can be exploited. In the long-term monitoring of winter months, the average temperature in the Quebec City region has been -15°C, with a snow cover thickness of 200 – 300 cm. In summer months, the average air temperatures have exceeded 25°C, and during the day, the temperature can be 40°C (Meteorological Service of Canada, 2016). The Baltic Sea region hardly ever witnesses such severe winters or hot summers.
Cold, heat and all other stress factors increase a plant’s energy consumption, irrespective of the locality. In viticulture, a temperature of 40 – 45ºC lasting for a few days will not hamper the growth. Only after the heat, drought and intense sunshine have lasted for several weeks will they destroy unprotected grapevines. Due to the stress caused by heat, grapevines do not grow near the equator. Therefore, the zone of grapevine growth has been 30 – 50 latitudes south and north of the equator.
The air temperature and snow cover thickness has a significant correlation (R2 = 0.58 – 0.74), that is, in severe winters, the snow cover protecting vegetation also increases. In cold winters with heavy snowfall, when the thickness of the snow cover is 70 – 80 cm, the temperature of the ground surface remains above -2.0ºC throughout the winter. During the winter of 2008 in Southern Finland, when there was an exceptionally low amount of snow, the lowest sub-zero temperature in January was -25.4°C and the ground surface temperature under the 18 cm snow cover was -8.7ºC, but at the depth of 40 cm, the soil temperature remained above 1 °C, and the grapevines did not suffer significantly.
The snow cover and layer of soil together protect the roots of grapevines in the winter. Despite the 10 – 32 cm thick snow layer, frost rarely reaches a depth of 40 cm in the southern parts of Northern Europe (Karvonen, 2002; Karvonen, 2008), because winters with low snowfall are mild there. Then, just the surface ground layer is sufficient insulation to protect the roots from frost. In viticulture, the situation is critical when there is a 2 – 3 week cold spell in early winter when the ground is still bare. That is when root damage may occur.
Severe sub-zero temperatures, heavy snowfall and cold spells may also occur in the wine-producing areas of Central Europe, even late in the spring. Such spells are usually shorter than in Northern Europe, but may damage new buds or shoots just starting to grow and delay the ripening of the crop. In 2011, the last period of frost in the Czech Republic took place at the beginning of May. On May 4, 2011, -7 ºC was measured in the Litomerice region and 70 cm of snow fell (Czech Hydrometeorological Institute, 2011). However, this short cold spell lasting a few days did not significantly damage the grapevines, and they continued to grow in the summer in the usual manner.
In a cool climate, grapevines growing in the open are protected by nature’s own cover, that is, snow and weeds, as well as hay and straw mulch spread between the rows, or with industrial frost gauze and plastic films protecting the roots. The most common artificial cover is black polyethylene film. Translucent greenhouse plastic has also been used as cover, as well as coloured plastic films letting light of different wavelengths pass through.
Sunlight cannot penetrate a black plastic cover, but the cover accumulates the radiation energy, which heats the soil and lengthens the northern growing season of 180 – 200 days by 2 – 4 weeks (Bauer, 2002; Ibanez et al., 2011). Irrigation with warm water has been used for growing vines in the open to heat the soil in the spring, making the growing season start 2 – 3 weeks earlier (Karvonen, 2002).
The temperature increasing impact of covers and black plastic film at the growing place reaches the planting depth below the ground surface. In summer, the black polyethylene film promotes the growth of 1 – 2 year-old vines, because it increases the soil temperature and, at the same time, retains the moisture of the soil (Sölva, 1970; Bauer, 2002).
Black plastic film increases the soil temperature and protects the roots of grapevines
In 2014 – 15, the impact of black polyethylene film of 0.07 mm on the subsoil temperature at a depth of 40 cm was monitored year round. The temperature variation of the soil in different seasons of the year is lower the deeper one goes. The soil temperature variation between winter and summer at a depth of 7 meters is minor, but even at a planting depth of 40 cm, it is somewhat less and slower that at the surface. (Lemmelä et al., 1981).
In the Helsinki region, due to the impact of the soil layer, which slows down temperature changes, the soil temperature in a vineyard with no cover in the summer reached its maximum at a depth of 40 cm about 2 months later than the air temperature. Under black plastic film, the soil temperature remained about 0.4°C higher year-round than that of soil with no cover. The difference is not very big, but it is statistically significant and may promote the growth of young vines during the growing season.
Greenhouse plastic used as cover does not increase the soil temperature in the same way as black plastic film, because its surface is too shiny and does not absorb the radiation energy of the sun like the black plastic film, but reflects a large part of the radiation back. It only increases the temperature of the soil and the environment when used in the roof and wall structures of greenhouses. There it creates an atmospheric greenhouse effect for the enclosure, which increases the greenhouse temperature early in the spring by letting the short-wave radiation energy of the sun through and preventing the long-wave ultraviolet radiation from escaping as heat dissipation. Therefore, the temperature of even a cold greenhouse already starts to rise so much during March-April that the growing season lengthens by 10 – 40 days (Novello and de Palma, 2008).
The wall of the house warms plants above the soil in the same way as the growing tubes in vineyards, but does not warm the soil itself. The stone base has a ‘cellar effect’.
In cool areas, grapevines are grown on the south