To find the side length of a square garden given its area, you can use the formula for the area of a square:
\[ \text{Area} = \text{side length}^2 \]
Given that the area is 144 ft², you can set up the equation:
\[ \text{side length}^2 = 144 \]
To find the side length, take the square root of both sides:
\[ \text{side length} = \sqrt{144} = 12 \text{ ft} \]
Therefore, the side length of the garden is 12 ft.