206 VEGETABLE FORCING 
most important factor. Slow growth develops bitterness 
and woody tissues. The time of harvesting should have 
careful consideration. Head lettuce cut too soon lacks 
firmness as well as quality, and loose-heading sorts cut too 
late are coarser and they lack flavor. Cleanliness and 
proper methods of marketing have an important bearing 
on the quality of lettuce. 
Fig. 69.—Head lettuce in the Boston district. 
Beds vs. benches.—A general discussion of beds versus 
benches will be found on page 38. Probably 95 per cent 
of the lettuce produced in the United States is grown in 
beds on the ground instead of on raised benches. Just 
as good crops may be grown in ground beds and at much 
less expense, all factors considered, as on benches. Let- 
tuce does not require bottom heat as much as do some 
other crops, though this is an advantage in hastening its 
maturity. Sub-irrigation on raised beds has proven 
highly satisfactory, but this method, for economic rea- 
sons, has not met with favor among commercial growers. 
Ground beds may be of any convenient width. They 
are seldom less than 5 feet and sometimes they are 12 to 
15 feet wide. Side boards or walls to the beds are some- 
times provided, as shown in Fig. 69, or they may be 
absent, as shown in Fig. 70. This is largely a matter of 
