Planting Date and Romaine Lettuce Cultivar Affect Quality and Productivity

The objective of this study was to determine the best combination of planting dates (PDs) and cultivars on yield and quality for long-term production of romaine lettuce. 'Green Forest' (GF), 'Apache' (AP), 'Darkland' (DK), 'Green Tower' (GT), 'Ideal Cos' (IC), and 'Tall Guzmaine' (TG) were successfully grown to harvest maturity on 19 PDs from September 1998 to April 2001. Lettuce planted in September and April PDs (pooled over cultivars and year), required as little as 47 and 49 days, respectively, to reach harvest (all cultivars harvested on the same day). Lettuce planted in October, November, February, and March PDs (pooled over cultivars and year), required on average 64, 66, 75, and 67 days to reach harvest, respectively, but in the coldest PDs of December and January, 90 and 98 days, respectively, were needed to reach maturity. Of the eight PDs evaluated, marketable numbers/plot (pooled over cultivars and years) were greatest in the September PD, followed by April (-8% decrease from September PD) > March (-13%) > October (-17%) > November (-21%) > December = January = February (about -30%) and heads weighed the most in September > January = February (-7% decrease from September PD) > March = April (-14%) > October (-21%) > December (-25%) > November (-31%). Cull heads/plot (pooled over cultivars and years) were greatest in April >December (-5% decrease from April PD) > January = February (-16%) > November (-27%) > October (-34%) > March (-44%) > September (-49°/o). Two out of three November PDs were lost to freezing damage and this PD should be avoided. Significant bolting occurred primarily in the September and October PDs (in 1 of 3 years) with negligible bolting in the November, December, and January PDs, but bolting recurred again in the February, March and April PDs. Marketable numbers/plot (pooled over all PDs and years) were greatest for GF > GT (-7% decrease from GF) > AP (-8%) > IC (-9%) > DK (-11%) > TG (-21%). The interaction effect of cultivar × PD indicated that GF yielded the most marketable heads in 6 out of 8 PDs. The best performing cultivars by PD (pooled over years) were September and February = GF and IC; October = TG; November = AP; December, January, March.