Question
We have a Norway Maple (Crimson King) tree in our backyard (approximately 12 years old) which is starting to create a heavy shade and therefore causing the grass around it to die.  We were fine with grass around the tree until last summer.  Although we know that Norway maple trees are quite evasive, we can't bear to cut it down since it's so healthy (it was already on our property when we bought the house).  Last night we pruned some of the branches back to let more sun filter in.  My questions are:  (1) Would putting river rocks (with landscaping fabric underneath) around the base of the tree going out 3 feet in diameter cause the roots to suffocate?  We were hoping to cover the base with the river rocks and then trying to grow grass on the outer perimeter of the trees.  (2) As well, would annually pruning the tree help the grass around it to grow or is growing grass a lost cause with Norway maple trees?
Thank you very much.

Answer
The rocks would harm the tree. I would use mulch and do not put more than 3 inche deep and not pile it up on the trunk. The landscaping fabric will help keep the weeds and gras from coming up in the mulch.

If an area gets less than 4 hours of sunlight per day, it is too shady for grass to grow well. The lack of sufficient light reaching the grass causes a reduction in photosynthesis, which is the process that produces energy for growth. As a result, the plant has lower tolerance to heat, cold, disease, drought and wear stress.

Certain grasses perform better in shade than others. Of the cool-season grasses, fine fescues are more tolerant of shade than tall fescues. St. Augustine exhibits the best tolerance to shade of all the warm-season grasses. Recommended St. Augustine cultivars for the coastal and midland areas include Raleigh, Palmetto, Delmar and Jade. Bitterblue and Seville are less tolerant of cold but grow well in coastal areas. Zoysia is more tolerant to light or moderate shade than centipede, but neither will survive heavy shade. Zoysia cultivars that have good tolerance to shade include El Toro, Diamond, Belaire and Cavalier. Meyer and Emerald have fair tolerance. Bermuda exhibits extremely poor tolerance to any amount of shade.

Pruning trees with dense canopies, such as maples, will allow additional light to pass through to the turfgrass sward. Prune lower branches to a height of six feet. On large trees, branches should be removed all the way back to the trunk or a main leader so that the area under the canopy is clear. Success with growing grass in shade can be increased if the tree canopy is thinned and branches from the lower third of the tree are selectively removed.