i8 The: Colorado Experiment Station. 
out new leaves which will take the place of the injured ones 
Prevention of Frost Injuries in General .—As this is a subject 
that would require a bulletin to be satisfactorily handled, we will 
give only some of the most important features concerning orchard 
heating. The following conclusions were drawn after consulting- 
over forty of the leading orchardists of the State who had used 
orchard heaters: 
1. The fact that every orchardist, who had been interviewed 
upon this subject, claimed that the orchard heater is a good invest¬ 
ment as an assurance in the fighting of frost, indicates that the 
orchard heater has come to stay. 
2. The oil heater is usually preferred over the coal, when 
more than five acres are to be heated, because of its more econom¬ 
ical maintenance. 
3. On cold, windy nights orchards with low headed trees 
receive more benefit from the heaters than high headed ones. 
4. Good thermometers well tested should be in the orchard 
as well as on the outside. 
5. Careful study of the stage of growth of the fruit buds 
should be made to ascertain their hardihood against frost injuries. 
I11 regard to the stage of growth of the fruit buds, bloom and 
set fruit of peaches and apples, as compared to their resistance to 
frost, the following opinions are given: Prof. W. L. Howard 
^states that in Missouri fully dormant peach buds can stand 8 or 
o degrees below zero. When appreciably swollen, zero is the dan¬ 
ger point. When the buds are showing the pink, they can stand 15 
degrees above zero. W hen the petals are off they stand 30 degrees 
above zero. For apples, when the petals begin to show, they can 
possibly stand a temperature of from 20 to 22 degrees above zero. 
From this stage on their resistance to cold becomes less and less as 
growth progresses. 
Prof. P. J. O’Gara fstates that, in the Pacific Northwest, 
peaches in bud are injured by a temperature of 29 degrees F.; in 
blossom by 30 degrees, and set fruit by 30 degree F. Apples in 
bud are injured by a temperature of 27 degrees; in blossom by 29, 
and set fruit by 30 degrees F. 
Prof. O. B. Whipple ifound that it is doubtful if, in Colorado, 
a temperature of 30 degrees F. will injure fruit or buds, in any 
stage of growth. That a temperature of 28 degrees, if of long 
enough duration to freeze the tissues solid, will kill peaches in 
* Reprint from the Annual Report of the Missouri State Board of 
Horticulture, 1909. 
tFarmers’ Bulletin No. 4 01, U. S. Dept. Agr. 
JFruit Growing in Arid Regions, by Paddock and Whipple, p. 3 53. 
The MacMillan Company. 
