2.3. Transplanting procedures
Transplants of ‘Sunbelt’ romaine lettuce and alyssum were produced in a commercial greenhouse
in 2.5 square by 5 cm deep cells in plastic trays for transplanting
35–40 d later. Lettuce transplants contained one plant
per cell, whereas alyssum transplants had an average of nine and
16 plants per cell in 2008 and 2009, respectively. In this paper,
‘transplant’ refers to a single lettuce plant grown in one cell or a
group of 9–16 alyssum plants grown in one cell. Alyssum transplants
grown for beneficial insect habitat in this region typically
contain multiple plants per transplant plug because seed singulation
is not possible with small raw seed that is used for the automated
system for seeding transplant trays; furthermore, raw
alyssum seed is inexpensive (approximately U.S. $ 30–55 per kg)
and transplant plugs with multiple plants are easier to pull from
the transplant tray (with less plant damage) and load by hand in
a mechanical transplanter. A hand loaded cell-type carrousel transplanter
was used to transplant the lettuce in two rows (Fig. 1) at a
density of 65,333 transplants per ha on May 4 and 5 in 2009 and
2008, respectively. After transplanting the lettuce on all beds, the
seven intercropping treatments with alyssum at various densities
and arrangements (Fig. 1) were created by hand with a trowel as
needed by replacing lettuce transplants with alyssum in the
replacement treatments, or adding alyssum between lettuce in
the additive treatments.