THE ONION IN COLORADO 
E. R. Bennett* 
Onions may be grown in nearly all parts of Colorado but, so far, they 
have been grown commercially in only a few districts. These are. in order 
of their importance,—the Uncompaghre Valley with Olathe as the center, 
Greeley, Denver, Pueblo, Rocky Ford, Canon City, and, to a less extent, 
near the other towin.s of the irrigated districts. The requirements for com¬ 
mercial onion growing are, first, a fairly long growing season; second, a 
soil that can be made fine and that will work easily, a great quantity of 
available plant food, and a sufficient water supply. 
SOILS 
Quite a variety of soils are used for onion growing. In the east' the 
most common soil is that known as muck, or peet, bottom lands. These 
soils are rich in nitrogen, hold moisture readily and when fertilized with 
ashes or other commercial fertilizers containing phosphoric acid and potash, 
grow good crops of onions, providing they are not handicapped iby either 
too much or too little rain,fall. Practically no soils of Colorado are of this 
class. The next most common soil for the culture of the onion is the loose 
soil of the river bottoms. These range from light sandy loam with consid¬ 
erable humus to the heavier adobes. Ini the east few onions are grown 
in the uplands, but this is largely a matter of availability of moisture. In 
Colorado, this makes comparatively little difference where irrigation is 
given and onions are grown successfully on the heavy |clay mesa soils. 
Ordinarily, the onion is not well adapted to light, dry gravelly soils, as it 
is difficult to get a sufficient yield to make the growing of onions a paying 
proposition. 
PREPARATION OF THE LAND 
Too much attention cannot be given to the preparation 1 of the land. 
Probably the best method of preparing land for onions is to plow up clover 
or alfalfa soil and grow some hoed crop that requires a great amount of 
cultivation, as the potato or sugar beet. Soils which have been planted to 
potatoes following alfalfa or clover are in excellent condition for onion 
growing. They always need, however, a heavy coat of well decomposed 
stable compost. For this reason, onion growing is largely confined to close 
proximity to the small towns or cities where stable compost can be hauled 
to the land without great expense. The most successful growers use 
from ten to twenty tons of this compost each year on their onion lands. If 
this ca’n be distributed in, fall and plowed in, so much the better. In fact, 
fall plowing for onions is to be desired, particularly on soils that are in¬ 
clined to be somewhat lumpy. In many cases, the manure is hauled onto 
the land during winter and plowing is done in February or March as soon 
as the frost is sufficiently out of the soil to permit the working of the land. 
In our districts of little rainfall, as in the Uncompaghre Valley, this may be 
depended on in the majority of years. The important thing in the prepara¬ 
tion of the land is to have it so thoroughly levelled that water may be dis¬ 
tributed over the whole field in shallow ditches or by flooding without 
getting too much in any one place: or leaving spots with insufficient water. 
Thorough preparation of the land by harrowing and flooding is necessary. 
This should be done until a perfect seed bed is made. 
So far, no particular rotation of crop has been practiced. The proba¬ 
bilities are that in time some rotation will need to be adopted to prevent 
the ravages of fungous diseases and insect pests, as the mildew, thrip, etc. 
The trouble with rotation in onion growing is the same as that for other 
intensive crops, that good onion lands are usually high in price and the 
grower feels that he cannot afford to give the land up for a year or two to 
such crops as clover or peas, as those crops will not, during those years, 
bring a good interest on the value of the land. 
*Former Horticulturist of Experiment Station. 
