title: How to add multiple geom_smooth lines to the legend (ggplot)?
body: <p>I am trying to create a plot which includes multiple geom_smooth trendlines within one plot. My current code is as follows:</p>
  
  <pre><code>png(filename="D:/Users/...", width = 10, height = 8, units = 'in', res = 300)
  ggplot(Data) + 
    geom_smooth(aes(BA,BAgp1),colour="red",fill="red") + 
    geom_smooth(aes(BA,BAgp2),colour="turquoise",fill="turquoise") + 
    geom_smooth(aes(BA,BAgp3),colour="orange",fill="orange") + 
    xlab(bquote('Tree Basal Area ('~cm^2~')')) + 
    ylab(bquote('Predicted Basal Area Growth ('~cm^2~')')) + 
    labs(title = expression(paste("Other Softwoods")), subtitle = "Tree Level Basal Area Growth") +
    theme_bw()
  dev.off()
  </code></pre>
  
  <p>Which yields the following plot: <img src="https://i.stack.imgur.com/7oHrE.png" alt="image of current plot"></p>
  
  <p>The issue is I can't for the life of me include a simple legend where I can label what each trendline represents. The dataset is quite large- if it would be valuable in indentifying a solution I will post externally to Stackoverflow.</p>