Romaine Lettuce

I start growing Romanian lettuce this week, hope to get some yummy organic salad.

Romanian Lettuce is somewhat sensitive to excess light (i.e., the crop gets saturated at 11 MJ/m2/d and levels of 19 MJ/m2/d or higher actually inhibit growth. If grown in high light regimes, the crop requires shading for optimum growth and yield.
Lettuce strongly responds to CO2 enrichment particularly at low light. At low light there is over 50% yield increase between enriched (1,000 mg CO2/kg) and non-enriched (400 mg CO2/kg).
For lettuce, optimum water supply is critical during vegetative and reproductive growth. Water stress, caused by high water demand and high air and soil temperatures, is the main cause for poor growth in the tropics. If exposed to water stress, the crop exhibits slow growth and tip-burn.

Temperature affects plant growth and yield of the lettuce. The threshold night temperature for plant growth is about 50 ºF providing that day temperatures are at least 50 ºF higher. Optimum growth is attained at night and day temperatures of about 53.6 and 75.2 ºF, respectively. Mean daily temperatures higher than 69.8 ºF promote seed stalk elongation, puffy heads, bitterness, and an increasing tendency toward internal disorders. Temperatures below 55.4 ºF, in turn, sharply reduce plant growth and N uptake.