I put some spikes in this Spring on my trees and I haven't noticed any grass dying or grass growing any faster. They say you are supposed to put them under the drip line of the tree because that is usually where the roots extend too. In this case you are just planting the tree the roots will only be the size of half your hole so just pound them down on the outside of the hole you dig, better yet bury the stakes as you backfill your hole then you solve the breaking issue as well as the grass issue..
| 
