30 MISC. PUBLICATION 650, U. S.. DEPT. OF AGRICULTURE 
exception of slightly superior yields from plots receiving only muriate 
of potash. These investigations agree with the observations of growers 
that pyrethrum apparently yields satisfactorily even on relatively in- . 
fertile soils, provided that good seed stocks are used and climatic 
conditions are of the best. 
Thorough soil preparation, particularly to eliminate grasses and 
weeds from the field and to provide for rapid drainage, is important to 
successful culture. Often it is a practice to ridge the land and to set. 
the transplants on the ridges. Recommended planting distances vary, 
but as a general rule the rows should be 2% to 3 feet apart, and indi- 
vidual plants may be set at intervals of 12 to 15 inches in the rows. 
The planting itself can be done by hand with a dibble or witha mechani- 
cal planter, such as is used for setting tobacco and cabbage. It is 
important in successful pyrethrum culture to avoid covering the crowns 
of the plants with soi!, both when they are being placed in the field 
and subsequently when the ground around them is cultivated to elimi- 
nate weeds. Soil spread over the crowns is likely to induce rotting, 
particularly if it becomes damp. 
Insofar as climate is concerned, it has been demonstrated that 
pyrethrum is tolerant both of summer heat and winter frost. However, 
for maximum flower production, it should enter a winter dormant 
period, which in the Tropics may not be possible at altitudes of less 
than 6,500 feet. Field trials in Kenya indicate that near the Equator 
the minimum may be 7,000 feet. Once established, pyrethrum is 
relatively drought-resistant, but for maximum yields it must receive 
adequate rainfall or irrigation water during the period of flower 
formation. 
Harvest 
In the Tropics, even at high altitudes, it is the general habit of 
pyrethrum to blossom throughout the season of active growth, although 
there are certain times, particularly following extended rainy periods, 
when flowering becomes heavier than normal. In temperate climates, 
where the winter dormancy period is prolonged, most plants iaay come 
into flower at about the same time early the following summer. In 
sections of the United States where plantings have been made, the 
flowering takes place over a period of a few days, during which all but 
a small proportion of the blossoms are at the desired stage for harvest- 
ing. This makes mechanical picking feasible, and some methods 
reasonably successful under certain conditions have been devised. 
Entire plants may be cut off with mowing machines, or binders, and 
hauled to stationary mechanical strippers, which remove and separate 
the flower heads. Research workers (28) of the United States Depart- 
ment of Agriculture have developed a tractor- or horse-drawn field 
harvester (fig. 16) which has proved efficient in most of the trials made 
with it. 
In the major commercial producing areas of the world hand picking 
by one means or another is the usual practice. Often the flowers are 
simply plucked singly by women and children (fig. 17). In some cases 
a scooplike box, fitted with a spike-toothed comb, may be used to strip — 
flowers in the field. In Japan it is reported that plants are often cut 
with a sickle and the flowers removed by pulling the stems through a _ 
comb stripper mounted on the edge of a box. 
