DRY-LAND GARDENING AT MANDAN, N. DAK. 3 
Table 2. — Dates of last frost in spring and first frost in fall, with temperatures 
recorded, and number of frost-free days at the Northern Great Plains Field 
Station for the five years from 1920 to 1924, inclusive 
Last frost in spring 
First frost in fall 
Frost-free 
period 
(days) 
Year 
Date 
Tem- 
perature 
(° F.) . 
Date 
Tem- 
perature 
(°F.) 
1920 
Apr. 27 
May 14 
Apr. 25 
May 14 
May 24 
18 
28 
29 
29 
23 
Sept. 28 
Sept. 30 
Oct. 7 
Oct. 4 
Sept. 26 
28 
31 
26 
32 
31 
154 
1921 
139 
1922 
165 
1923 
143 
1924 
125 
May 9 
Oct 1 
145 
GARDENING EXPERIMENTS 
As a workable rotation system and the judicious selection of vari- 
eties are of interest and importance to gardeners on the northern 
Great Plains, the results over an extended period of time in the 
garden at the Northern Great Plains Field Station are presented in 
detail. 
EXPERIMENTAL METHODS 
The size of the garden is approximately an acre. Its dimensions 
are 160 feet north and south by 272 feet east and west. The rows 
run north and south. 
A definite four-year rotation system and a well-matured planting 
plan are followed. Standard varieties are used, and the seed for them 
is obtained from the same sources each year. 
The length of row or number of hills of each vegetable is approx- 
imately constant from year to year, and is based on tentative esti- 
mates of the quantities required for a family of five, with possible 
small surpluses for disposal. Wide spacing is practiced. 
Each vegetable is harvested when it is ready for the table or for 
market or storage. The yields are determined and the records kept 
in units of quarts, pounds, fruits, etc., according to the market 
practice with the different vegetables. 
THE ROTATION SYSTEM 
An adequate system of rotation in a garden offers three advantages : 
(1) The accommodation of the various vegetable crops to their differ- 
ent requirements for manure and soil moisture; (2) the elimination 
of plant diseases and insect pests; and (3) the use of a permanent 
garden site, which enables the grower to provide necessary shelter 
with windbreaks or hedges. Various parts of different vegetables 
are made use of as food, such as the fleshy roots of some, the succulent 
leaves of others, and the fruits and seeds of still others. Accordingly 
they may be classified as root crops, leaf crops, etc. Each crop has 
special requirements of soil, fertilizers, and moisture for its best de- 
velopment. The rotation system in use at the field station is based 
on these requirements. 
The vegetables are divided into four classes or groups, as follows: 
Leaf crops, root crops, leguminous crops, and vine crops and early 
