Climate Zones and Planting Dates for
Vegetables in Ontario
Introduction
Most vegetable production is concentrated in Southern Ontario. There are
differences in climate even in this small area. The length of the growing
season and average temperatures can vary greatly from one area to the next.
Vegetable crop development is usually referred to by the number of "days to
maturity." This measure indicates the average number of calendar days from
planting to harvest maturity. However, due to variability in daily temperatures
and light intensity, this measure of "days to maturity" does not always reflect
the rate of crop growth under actual growing conditions.
Climate Zones
Figure 1, Climate Zone Map of Ontario (1976-2005), shows the Ontario
climatic zones based on the average frost-free period. This updated climate
zone map of Ontario was created using a larger dataset than the previously
published 1961-90 map. As a result, the amended zones reflect a higher
degree of accuracy when compared to the previous version.
Figure 1. Climate Zone Map of Ontario (1976-2005). Source: Weather
Innovations Incorporated
Text Equivalent of Figure 1
Zone A, in Essex and parts of Kent County, has the longest growing season.
The growing seasons of the other zones are progressively shorter. The zone
lines on the map are approximate and do not represent sharp changes in
climate. The length of the growing season and temperatures change gradually
from one zone to another.
Table 1, Average Frost-Free Period in Climatic Zones of Ontario (19762005) gives the average dates of first and last frost (0°C) for each zone.
Table 1. Average Frost-Free Period in Climatic Zones of Ontario (19762005)
A
Frost-Free Period
(Average in Days)
170-190
Average Date of Last Average Date of
Spring Frost
First Fall Frost
April 25
October 20
B
160-170
April 30
October 13
C
150-170
May 3
October 8
D
130-165
May 11
October 1
E
125-145
May 17
September 26
F
115-125
May 24
September 22
G
100-115
May 27
September 17
H
100-110
June 3
September 16
I
90-100
June 7
September 9
Zone
Risk of Frost
The dates listed in Table 1 indicate that 50% of the time (one year in two)
there will be no frost in these locations after that date. There is a 25% risk of a
frost occurring 7 days after the listed last spring frost date. Fourteen days after
the listed date, the risk decreases to 10%. Conversely, there is a similar risk
factor associated with frost occurring before the first fall frost dates.
Note that the frost dates in Table 1 refer to the occurrences of 0°C at a
standard height of 1.5 m, at which time tender crops will often be damaged.
Frost-hardier crops are not usually damaged until temperatures at this height
drop below -2°C. The date of occurrence of -2°C is usually about 2 weeks
earlier in the spring or later in the fall than the dates mentioned in the table.
For a list of vegetable crops and their comparative hardiness, see Tables 2a-
2d, First Field Seeding or Planting Dates for Commercial Production.
Growing conditions are also influenced by local variations in topography,
altitude, natural air drainage and proximity to water. Cold air tends to flow
into low-lying areas. Plants at the bottom of a slope are often the first to suffer
frost injury. Local variations must be considered in deciding the location and
time of planting.
For more information on recommended planting conditions, see OMAFRA’s
vegetable publications,
http://www.omafra.gov.on.ca/english/crops/vegpubs/vegpubs.htm
Table 2a. First Field Seeding or Planting Dates for Commercial Production Frost Hardy Crops
Crops
Asparagus, broccoli,
Brussels sprouts,
cabbages, lettuce,
onions (set, seed,
Spanish), radishes,
rhubarb, peas, spinach,
parsnips, early potatoes
Zone A
Zone C
Zone E
April 1 - 15
April 15 - 25
April 25 May10
Table 2b. First Field Seeding or Planting Dates for Commercial Production Semi-frost Hardy Crops
Crops
Beets, carrots,
cauliflower, celery, late
potatoes, early sweet
corn
Zone A
Zone C
Zone E
April 15 - 25
April 25 - May
10
May 5 - 15
Table 2c. First Field Seeding or Planting Dates for Commercial Production Semi-frost Tender Crops
Crops
Snap beans, sweet corn,
tomatoes
Zone A
Zone C
Zone E
May 1 - 15
May 15 - 25
May 25 - June 5
Table 2d. First Field Seeding or Planting Dates for Commercial Production Frost Tender Crops
Crops
Lima beans, cucumbers,
eggplant, muskmelons,
peppers, pumpkins,
squash, watermelons
Zone A
Zone C
Zone E
May 20 - 30
May 25 - June 5
June 5 - 15