Vegetable Growing in Colorado. 
39 
hardening off plants such as tomatoes or cabbage, it is not neces¬ 
sary to make an excavation unless to make room for a few inches of 
good soil. The soil in a cold frame may be the same as that for a 
hotbed, or a good sandy, loamy garden soil will be sufficient. 
If the cold frame is to be a permanent structure, the sides 
should be made of heavy plank two inches thick or of brick or ce- 
* 
ment. If it is desired to use it for carrying half hardy flowers in 
pots over the winter an excavation three feet deep may be made and 
the walls and bottom cemented. Sawdust is then put in to a depth 
of a few inches and the pots are plunged in this to the rim. 
Hardy plants like cabbage, kale, and cauliflower can be carried 
through the winter in cold frames in order to have them for early 
transplanting in the spring. The seed are sown in the open in the 
fall in time to develop three or four true leaves before freezing 
weather comes on. When the plants are transplanted into tne cold 
frames they should be as stocky as possible. All weak or poorly 
developed plants should be discarded, as they will hardly survive the 
winter. When freezing weather comes on, the frames are covered, 
but they should be left open as late as possible in order to make the 
plants more hardy. The sash is first put on and later the covers are 
used. The plants do not grow during the winter. They gradually 
freeze, but if proper care is exercised that the sun does not strike 
the frozen plants and thaw them out too quickly, they will come 
through unharmed. They may stand for several days under a cover 
of snow on the sash without injury with the ground frozen, but if 
the ground should thaw out, they should not be kept in the dark 
for more than a day or two at a time. When warm weather comes, 
the plants are thawed out as gradually as possible and the sash is 
removed on bright warm days. ' 
The proper age and condition at which plants should go into 
the cold frame can be determined only by experience. If the plant 
is too old when put into the cold frame, it is apt to run to seed when 
planted out in the spring, and if it is too young it will not be likely 
to survive the winter. 
Such plants as pansies, carnations and daisies may be kept over 
winter in the ordinary cold frame without any trouble. 
The best use to which cold frames can be put in this climate 
is that of hardening off plants in the spring. If tomatoes, cucum¬ 
bers and other tender plants are started in the hotbed or green¬ 
house, it is better to transplant them into a cold frame for a short 
time before they are finally put in the field. By this means they are 
gradually accustomed to a lower temperature and yet may be pro¬ 
tected on cold nights. 
