S. DEPARTMENT OF AGRICULTURE 
CLIMATE 
The climate of the northern Great Plains is not well adapted to 
general horticulture. The scant precipitation; the frequent winds 
sweeping over the generally unprotected farmsteads; the nigh rate of 
evaporation, generally highest in the seasons of lowest precipitation; 
and the short growing seasons, indefinite because of irregularity in 
the dates of killing frosts in the spring and fall, are difficulties with 
which the growers in this region must contend. 
Complete climatic data have been recorded at the station since its 
establishment. Similar records have been kept since 1875 by the 
United States Weather Bureau station at Bismarck, N. Dak., 5 
miles east of Mandan. 
The 50-year mean annual precipitation is about 17 inches. The 
month of maximum precipitation is June, with a mean of more than 
3.5 inches, and the month of minimum precipitation is February, 
with less than 0.5 inch. 
The average date of the last killing frost in the spring is about 
May 15 and that of the first in autumn is about September 15, but 
frost has occurred as late as June 3 and as early as August 23. 
The prevailing wind direction is from the west or northwest. 
The average wind movement near the ground is about 6 miles an 
hour. 
The monthly, the seasonal, and the annual precipitation at the 
field station for the five years from 1920 to 1924, inclusive, for which 
results with vegetables are reported in this bulletin, are given in 
Table 1. The period was one of unusually protracted drought. 
The annual precipitation averaged only 15.19 inches, and equaled 
the long-time average in only one of the five years. 
Table 1. — Monthly, seasonal, and annual precipitation at the Northern Great 
Plains Field Station for the five years from 1920 to 1924, inclusive 
Year 
Jan. ! Feb. Mar. 
1 1 
Apr. 
May 
June 
July 
Aug. 
Sept. 
Oct. 
Nov. 
Dec. 
Seasonal, 
Apr. to 
Sept. 
An- 
nual 
1920 
1921 
1922 
1923 
1924 
0. 52 0. 20 
. 18 1 .09 
.28 ; 1.55 
.36 .38 
.03 .25 
1.21 
.79 
.52 
.16 
.28 
0.58 
2.59 
.66 
1.85 
1.68 
1.72 
3.05 
2.05 
1.18 
.41 
1.85 
.82 
3.43 
1.94 
5.56 
2.68 
3.38 
3.17 
4.12 
2.07 
1.81 
.25 
.32 
1.15 
2.35 
1.29 
1.58 
2.31 
2.31 
1.34 
0.25 
1.39 
.64 
.54 
1.94 
0.37 
.87 
1.60 
.28 
.06 
0.21 
.24 
.82 
.14 
.28 
9.93 
11.67 
11.94 
12.55 
13.41 
12.69 
15.23 
17.35 
14.41 
16.25 
From 69 to 87 per cent of the entire precipitation each year, how- 
ever, was received during the growing season, from April to Sep- 
tember, inclusive, and annual crops, such as most vegetables, were 
enabled to obtain the maximum benefit from it. 
The dates of the last frost in the spring and the first frost in the 
fall and the length of the frost-free period for each of the five years 
under study are given in Table 2. During these five years the latest 
frost in spring was on May 24 and the earliest in fall on September 
26. The frost-free period varied from 125 to 165 days and averaged 
145 days. 
