Meaning of the first digit : General growing place :
2 : WOODLAND EDGE. Plants for a more or less open space with an occasional tree or shrub. In principle occasionally some sun.
Meaning of the second digit: Specific demands :
1 : Plants close to trees or shrubs, but in the sunshine.
Meaning of the third digit : Where to put :
3 : For rich, well-drained, dry to lightly humid soils.