You want to make a stacked bar graph.

Use geom_bar() and map a variable fill. This will put Date on the x-axis and use Cultivar for the fill color, as shown in Figure 3-16:

library(gcookbook) # For the data set
ggplot(cabbage_exp, aes(x=Date, y=Weight, fill=Cultivar)) +
    geom_bar(stat="identity")

Figure 3-16. Stacked bar graph

To understand how the graph is made, it’s useful to see how the data is structured. There are three levels of Date and two levels of Cultivar, and for each combination there is a value for Weight:

cabbage_exp

 Cultivar Date Weight        sd  n         se
      c39  d16   3.18 0.9566144 10 0.30250803
      c39  d20   2.80 0.2788867 10 0.08819171
      c39  d21   2.74 0.9834181 10 0.31098410
      c52  d16   2.26 0.4452215 10 0.14079141
      c52  d20   3.11 0.7908505 10 0.25008887
      c52  d21   1.47 0.2110819 10 0.06674995