Concept:
Vertical gardening is a method of growing plants vertically on walls, panels, fences or other vertical surfaces.
Step 1: Check Assertion.
A vertical garden may be a free-standing wall or vertical structure covered with vegetation.
\[
A \text{ is correct}
\]
Step 2: Check Reason.
A blank wall or fence can be made green by using the concept of vertical gardening.
\[
R \text{ is correct}
\]
Step 3: Check explanation.
Reason gives an application of vertical gardening. It does not directly explain the definition given in Assertion.
\[
R \text{ is not the correct explanation of } A
\]
\[
\therefore \text{Correct Answer is (B)}
\]