The Ground Beneath Fruit Trees

I was at someone's house the other day and they had small rocks covering the ground beneath a lemon tree. Is that okay to cover the ground with rock beneath a fruit tree?

Is it important to keep the ground clear from everything including grass and weeds beneath a tree?

Or is it okay to plant some small perennial flowers under there. I've heard conflicting opinions on all these things. Is there a rule of thumb?

thank you

 

Tree will grow better with mulch (rocks, in this case) - same as any other kind of tree or shrub. The only thing different about fruit trees is you do not want to have anything placed or growing beneath them that would get in your way or otherwise be a bother during maintenance (pruning, spraying) and harvesting activites.