The Climatic Potential for Grape Growing in the Peterborough Region
A thesis by Elise Ho parts of which were presented to
the Second Annual Central Ontario Viniculture Association Seminars
by Dr. Graham Cogley of the Geography Department of Trent University

Editing note: Pertinent items were selected from Ms. Ho's thesis by me to fit the record of the day and the needs of those who will look here. Please contact the Geography Department at Trent University for fuller documentation (about 80 pages, not available electronically).

Abstract

This study examines the climatic potential for grape growing in the Peterborough region, with emphasis on temperature and radiation. The main constraints on grape growing in Peterborough are the colder temperatures and shortened growing season, as compared to the Niagara and Point Pelee regions of Ontario. In order to maximize the climatic potential for grape growing in higher latitudes, equatorial facing slopes are often chosen as planting sites as they generally maximize incoming solar radiation at the surface, thus extending the growing season and positively affecting plant growth.

This study examined the temperature distribution of an agricultural site near Peterborough with equatorial facing slopes for a three-month period (November 22, 1999 through February 22, 2000) as well as historical temperature data from the Trent weather station from 1969 to February 2000. The study also examined the effect of a non-horizontal surface (represented by the study area) on direct solar radiation received at the surface.

The study found that the distribution of temperature over the study area was varied, so that different areas seemed to be warmer than others. The historical temperature record indicated that the heat summation (a popular method of determining a region’s climatic potential for grape growing) per year has been above the minimum requirement for cold-hardy cultivars within the past 30 years with the exception of 2 years (1981 and 1992). Extreme winter temperatures (-20oC and -23oC) were experienced throughout the temperature record, but did not occur for prolonged periods of time.

The general trend for yearly heat summation values in Peterborough was also found to be increasing. The study also found that the equatorial facing slopes of the study area received relatively more direct radiation as compared to a horizontal surface during the winter months and that during the summer months this difference is negligible.

In conclusion, the study found that the Peterborough region is likely to have the climatic potential to grow grapes, and that this probability is likely to increase in the future if temperatures increase as expected. Equatorial facing slopes are also likely to be good selections for planting, as they tend to increase the relative amounts of radiation received at the surface. The topography of a site may have significant effects upon the area's microclimate, thus the peculiarities of each potential site should be closely examined.

Introduction

Canada’s agricultural industry contributes about 9% of its gross domestic product (Britton, 1996). However, it is suspected that its strong role in Canada’s economy may decline in the coming years due to fierce competition abroad (often from "developing countries") offering greater amounts of produce in a wider variety at a much cheaper cost (White, 1990). In addition, Canada’s agricultural economy is hindered by many internal factors. The largest handicap is most likely Canada’s climate, which is unsuitable for crop production in most areas far north of the Canadian-American border. Ontario’s agricultural industry is concentrated in Southern Ontario and is the largest producer of vegetable and fruits in Canada (Britton, 1996). Nonetheless, of Canada’s total exports, fruits and vegetables only constitute 6.7% while of its imports, fruits and vegetables total 37.3% (Britton, 1996). Therefore, Canada is constantly trying to expand its agricultural sector not only to service its residents, but also in order to become a global competitor in the agricultural economy.

One of the most interesting fruit crops grown in Southern Ontario is the grape, which is typically thought of as a Mediterranean or Californian crop. Ontario is not generally thought of as having a suitable climate for the grape, but farmers have been able to maximize the Ontario’s grape growing potential in the Niagara and Point Pelee regions and to a lesser extent in the Toronto region. Thus since this crop is grown in such a small area of Southern Ontario, any extensions of the growing area would be highly beneficial to the tender fruit industry in Ontario.

There has been much interest concerning grape growing in the Peterborough region, which is north of the Niagara and Point Pelee regions and has a shorter growing season (by about 40 days per year) and a shorter frost-free period (by about 30 days per year) (Ontario Economic Atlas, 1969). In general, Peterborough is not thought of as a likely area for successful grape crops. However recently, there has been much private interest in bringing the commercial grape crop to Peterborough for wine production.

Presently, some residents of Peterborough successfully grow grapes on their residential property, but the microclimate of those residences is such that the houses tend to warm the surrounding air and thus create a more favourable grape growing environment. The possibility of growing grapes on a larger scale for commercial winery reasons is a different issue than private grape growing in the backyards of homes. Several individuals in the Peterborough community are involved with a new and small winery in Buckhorn, Ontario and are also interested in establishing a commercial winery in Peterborough.

It is thought that the only major constraint on grape growing in the Peterborough region is its climate, which is slightly colder and more extreme than the relatively moderate climate of the Niagara region. However, the possibility for bringing the grape as a commercial crop to Peterborough may exist. Unfortunately, because the winery in Buckhorn is relatively new and there are no wineries in Peterborough, there is great interest in determining the feasibility of growing grapes in Peterborough.

The aim of this thesis is to assess the climatic potential (with particular emphasis on temperature and radiation) for grape growing in the Peterborough region.

{Site owner Dr. Bryan Pell on part of the study area with 2nd Year Pinot Noir, 2001
click on picture to magnify it}

Study Area Description

The purpose of this thesis is to examine the climatic potential (specifically temperature and radiation) for grape growing in Peterborough, Ontario. Figure 2 shows a map of Southern Ontario with Peterborough (at 44.57oN), the Niagara region and Point Pelee region (at approximately 43.2oN and 42.0oN, respectively), which are the main grape growing regions of Ontario. Figure 2 also shows the growing regions of Southern Ontario divided on the basis of length of growing period (Dean, 1969). This shows that Peterborough has a shorter growing season than both the Niagara and Point Pelee regions.

The specific study area that this study is partially based upon is a privately owned farm located in the western portion of Peterborough, on the outskirts of the city. Figure 3 shows the location of the farm, which is south of Lily Lake Road and north of Jackson Creek. Figure 4 shows the field area, which is approximately 400m long and 260m wide, blocked to the north by fencing, to the east and south by a ridge of trees and to the west by the property owner’s home. Behind each boundary is another agricultural field, mainly bare of trees. The topography is gently sloped towards the south/southeast and is bare soil and soybean stubble from the previous year’s crop.

Trent Weather Station Record from 1969 to Present

Temperature data were obtained from the Trent weather station as daily minimum, maximum and mean records for the past 30 years. Figure 13 shows the mean daily temperatures recorded at the Trent weather station. Frost damage to many grape crops can occur when winter temperatures are colder than -20.0oC for prolonged periods of time. Some of the hardier varieties (such as American hybrids or some hardier cultivars of Vitis labrusca) may survive winter temperatures of -23 .0oC (Brown & Blackburn, 1987) while some of the most cold-hardy varieties (such as Riesling) can withstand temperatures of -26oC when fully acclimated (Jackson, 1994).

Figure 13 shows several instances of extremely cold winter temperatures, where the coldest winter temperature was -28.8oC in 1981. Table 3 summarizes the number of days per year that experienced temperatures less than -20oC and -23oC. It is evident that although extreme temperatures have been experienced in the Peterborough region, the average number of days per year that experience such cold temperatures is not large. Thus, while damage to the grape crop due to extreme temperatures may occur, the duration of such periods is, on average, not large. Therefore, it can be expected that mild to severe winter damage to the grape crop could occur every 5 or 10 years. Brown and Blackburn (1986) state that outside of the Niagara Peninsula, damage to 5 to 10% of the fruit crops can occur every 5 to 10 years. Therefore, it can be expected that damage to the grape crop in Peterborough due to extreme winter temperatures can occur on this cycle, but that for most other winters, severely cold weather will not be a major factor in crop loss.

Another indicator of the capacity for a region to support a grape crop is heat summation, measured in degree-days. Table 3 also summarizes the calculated degree-days for each year from 1969 to 1999 as obtained from the Trent weather station data.

Jackson (1994) states that cool-adapted eultivars require at least 1000 degree-days per year. Such cultivars include Pinot Noir and Chardonnay (Winkler et al., 1974). Figure 14 illustrates the heat summation values in graphical form with a trend line indicating that the number of degree-days per year has been (on average) increasing. Therefore, it can be expected that the Peterborough region can support a grape crop of the hardier grape varieties as its mean heat summation for the past 30 years is 1155 degree-days and this value is likely to increase in the future.

However the mean difference between site L (which was highly correlated to the data from the Trent weather station) and the weather station data for the three month period was 0.43oC, indicating that on average, the study area at site L is 0.43oC cooler than the Trent weather station. If the heat summation is recalculated for the 30 year period with a 0.43oC decrease in daily temperature, the mean heat summation is 1087 degree days. Still, this value is above the minimum requirement of 1000 degree-days per, so it can be expected that if the study area is slightly colder than the weather station, it may still be climatically able to support a grape crop.

Table 3: Frequency of Extreme Temperatures and Calculated Degree Days from Trent Weather Station Data 

     Year Number of Days         Number of Days             Heat
          Temperature < -20oC    Temperature < -23oC      Summation
                                                         Degree-Days

     1969                 0                   0             1071.5
     1970                 5                   0             1216.2
     1971                 4                   0             1182.9
     1972                 0                   0             1042.4 
     1973                 2                   0             1249.7
     1974                 0                   0             1003.0
     1975                 1                   0             1219.1
     1976                 6                   2             1059.0
     1977                 2                   0             1142.1
     1978                 0                   0             1068.6
     1979                 8                   3             1096.9
     1980                 2                   0             1072.0
     1981                 5                   4              989.5
     1982                 5                   2             1057.0
     1983                 1                   0             1217.4
     1984                 5                   1             1083.2
     1985                 0                   0             1082.3
     1986                 0                   0             1121.5
     1987                 1                   0             1276.5
     1988                 1                   0             1235.2
     1989                 3                   0             1189.7
     1990                 0                   0             1196.1
     1991                 0                   0             1392.8
     1992                 1                   0              900.8
     1993                 3                   0             1094.0
     1994                 9                   4             1136.4
     1995                 2                   0             1287.2
     1996                 4                   0             1204.9
     1997                 1                   0             1144.5
     1998                 0                   0             1411.2
     1999                 1                   1             1347.6
     Mean                2.3                 0.5            1154.6

Conclusions

Because the data obtained from most of the stations at the study area are somewhat uncertain, it is not practical to base any sort of temperature profile upon the three months of data obtained. However because sites L and J are highly correlated with the weather station data and exhibit few (if any) of the cold excursions that make the other stations questionable, it is possible to base a temperature profile for the study area upon these data. The mean differences between the weather station temperatures and Sites L and I are -O.43oC and -O.76oC, respectively. Thus while there may be a high correlation between the data, there is no large mean difference between the temperatures at the study area and the temperatures at the Trent weather station. Therefore, it can be assumed that the data at the weather station are a good indicator of the temperatures at the study area.

This indicates that in terms of temperature, there is the possibility that grapes can be grown fairly reliably at the study area. The yearly heat summation values and frequency of extreme winter temperatures indicate that while there is some extreme weather risk to grape crops, it is likely that on average, the grape crop will succeed in this region and this possibility is likely to increase in the future.

The radiation modelling also indicates that the topography is favourable to growing grapes, as increased relative amounts of direct radiation in the winter could possibly aid in the buds’ tolerance to cold (Zobel, 1999), and the increased levels of radiation could increase the growing season and amplify rates of photosynthesis (Jackson, 1994).

Still, the data are only provisional and there is still a fair degree of uncertainty in these data. To further this study, practical experiments involving planting of different varieties at different locations (preferably the south western portion or western portion) on the study area for several years would further results and help to answer the research question. Experimentation should also be conducted in order to determine possible and feasible methods of crop protection from winter temperatures.

COVA 2001 COVA Homepage www.littlefatwino.com