Step 4: Light setup
We will use the classic 3-point lighting; add a plane above Suzanne and set as the emission shader (strength 1, color pure white), an emission plane on the left side (warm light, strength 3) and another on the right side (cold light, strength 1). Move the camera and set the focal length at 50 millimeters. In the world tab, set strength as 0, change the view mode from solid to rendered and wait for a render test.
Step 5: Render setup
In the render tab, set render the samples to 500 and hit F12. If you want to create a more complex scene (more ivy, more mesh) set samples to 1000; don't forget that a lot of leaves need a long render time. In my scene, I created a box with a window on the top and a sun lamp outside; in this way light is stronger and shadows will make a more realistic stone material. Volumetric light was added in postproduction using Gimp.
Top tip 1: Random leaves color
In the real world, leaves aren't all the same, so we'll add a random color to our ivy. Select leaves and jump to edit mode. Separate the leaves (press P and choose 'by loose part'). Be careful if you have a lot of leaves as this action could freeze the PC! Now, in the node editor window add a color mix node (blend mode set as mix) between diffuse node and image texture. Add a color ramp node and set constant blend (select 3 or 4 colors, the length of the ramp will be the probability that a leaf takes the color). Connect color ramp to mix node. Add an object info node and connect the random output to the fact input of color node.
Random leaves colouring
Top tip 2
Unfortunately the plug-in only has 2 options about the growth of leaves; we can choose the probability that a leaf is created and its size. If we want more control, we can use a particles system. So, uncheck the grow leaves option in the IvyGen panel and use the plug-in to create a branch. In a different layer, add a plane (call it leaf) and add a leaf material as seen in step 3. Now convert Ivy to a mesh and add a particles system and choose Object > leaf in the render tab of the particles system option. Now we can control the number of leaves, dimension and rotation. The best way to control where the leaves grow is to use the 'weight paint' mode on branches.
Particles system and leaves