WiioKLBD Milkweed 
ir> 
Fig-. 11 — Showy milkweed. This plant is often 
supposed to be the poisonous milkweed. 
It is not known to be poisonous. 
ever, on the heavier clay type. It does especially well on the red 
clay loam of La Plata and Montezuma Counties and on the heavy, 
gray clay of the North Fork and Grand River valleys. It is not so 
well adapted to the lighter sandy soils. Alkaline soils produce a 
better growth than do acid soils, although from the salt spray ex- 
perimental work at Cortez, it appears that the alkalinity can be 
raised with common salt at least to such a percentage as to kill 
the milkweed without inhibiting the growth of such plants as 
Russian thistle. 
The altitudinal limit for Colorado seems to be somewhere in 
the neighborhood of 7,500 feet. Plants found at a little below this 
elevation did not appear to be as thrifty as plants at lower eleva- 
tions, nor have any extensive infested areas been found above 
