This is the 16475th most frequent Russian word.
садовом
"Садовом" means "garden" or "gardening" in a locative or descriptive sense.
Here, "садовом" is used as an adjective modifying "участке", describing the garden plot.
Я купил новый инструмент для работы в садовом участке.
I bought a new tool for working in the garden plot.
In this case, "садовом" serves as an adjective related to "фестивале", and refers to a festival themed around gardening or gardens.
Она рассказала о своих приключениях на садовом фестивале.
She talked about her adventures at the garden festival.
"Садовом" modifies "магазине", indicating the store specializes in goods for gardens.