The average date of the last spring frost is particularly important because it determines the date of planting. In addition, a late spring frost can do serious damage to young plants. The date of the first fall frost determines the end of the growing season for most crops.

A particularly important period is the time between the first spring frost and the last fall frost, defined as frost-free period. This is the time available for crop production. For most of the R.M. of Lansdowne, the average date of the last spring frost is May 19 to 24. The first fall frost in the R.M. of Lansdowne occurs, in most years, between September 11 and 16. However, on the eastern side of the RM, the first fall frost tends to be five days later.

The frost free period is defined as the number of days between the last spring frost and the first fall frost. The frost-free period determines the time available for crop production, and thus also determines what crops can be grown. The frost free period for the R.M. of Lansdowne averages between 115 and 125 days. This is one of the longest frost free periods in all of Manitoba.

Cereal grains such as spring wheat, barley, oats and buckwheat, as well as oilseeds such as canola, require a minimum accumulation of about 1,200 growing degree days above 5°C to reach maturity. The R.M. of Lansdowne averages 1600 to 1650 GDD, including 950 to 1000 GDD above 10°C, and 450 to 500 GDD above 15°C.

Corn heat units are a measure of useful heat for the growth and development of corn. Silage corn and grain corn hybrids are rated in relation to the corn heat unit (CHU) requirements. In Manitoba, silage hybrids require from 2,000 to 2,100 CHU annually while grain hybrids require 2,200 to 2,400 CHU to mature. The RM of Lansdowne has an annual average accumulation of 2,400 to 2,500 CHU.

Minimum temperature for potato growth and development is 7°C, while the most rapid growth and development takes place at 21°C. The growth rate decreases with the increase in temperature and finally stops at 30°C. P-Days are a measure of useful heat for the growth and development of potatoes. Most potato varieties require from 800 to 1000 P-Days to reach maturity. The R.M. of Lansdowne has between 800 to 850 P-Days. More information about growing potatoes in Manitoba can be found at the Government of Manitoba web site.

Growing plants require large amounts of water. The amount of water that would be used, if supply was unlimited, is referred to as "growing season crop water demand". Actual crop water demand depends on weather, the crop type and its stage of development.

The growing season for cereal and canola crops is defined as the period from planting to crop maturity. The growing season in the R.M. of Lansdowne, normally, is a period of 100 to 120 days. Recorded planting dates usually range from April 30 to May 20. On average, spring wheat matures between August 11 and 22.

Crop water demand during this period varies with two factors: Potential evapo-transpiration (PE) and the fraction of ground area covered by leaves.

PE is the maximum water use for a given set of weather conditions. Water demand varies from 30 to 100 percent of PE during the various stages of wheat development. Water demand is about 30 percent of PE when the crop emerges. It reaches 100 percent as soon as the ground is completely covered by the crop.

From planting to maturity, a wheat crop in Lansdowne requires an average of 275 to 300 mm (11 to 12 inches) of water. Average soil moisture available at planting for spring wheat is 170 to 200 mm. Average precipitation during the growing season provides an additional 180 to 210 mm - giving the crop a total potential supply of 350 to 410 mm of moisture.

Perennial forage crops like alfalfa cover the ground completely with actively growing leaves early in spring, and it remains covered for most of the growing season. Water demand for perennial forage approximately equals the PE. The average amounts to 400 to 450 mm (16 to 18 in.) per year. The R.M. of Lansdowne average need is between 425 to 450 mm.

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