Successful organic farming requires synchronizing soil-based processes affecting nutrient supply with crop demand, variable among and within crops. We report here on two studies conducted in transitional- (TO) and certified-organic (CO) systems containing subplots that, annually, were either amended with compost or not amended prior to vegetable crop planting. Dairy-manure compost was added at rates providing the portion of a crop's anticipated nitrogen requirement not provided by a leguminous rotation crop and/or carryover from previous compost application. In the TO study, potato (2003), squash (2004), green bean (2005), and tomato (2006) were planted in main-season plots in open fields and high tunnels, and beet, lettuce, radish, spinach, and swiss chard were planted in high tunnels in early spring and late fall. Long-term CO open-field plots (±compost) were planted to multiple varieties of lettuce, potato, popcorn, and processing tomato in 2004–2006. Drip irrigation was used in all TO plots and CO lettuce and processing tomato plots. Treatment effects on crop physical and biochemical variables, some related to buyer perceptions of crop quality, were emphasized in each study. Yield in TO, compost-amended plots exceeded yield in unamended plots by 1.3 to 4 times, with the greatest increases observed in high-tunnel-grown mesclun lettuce and the smallest response observed in potato. Similar results were found in CO plots, although compost effects differed by crop and variety. The data suggest that: 1) compost application and the use of specific varieties are needed to maximize yield in organic vegetable systems in temperate zones, regardless of age; and 2) production phase management may influence buyer-oriented aspects of crop quality.