Grass trees (genus Xanthorrhoea) look like they were imagined by Dr Seuss. An unmistakable tuft of wiry, grass-like leaves atop a blackened, fire-charred trunk.

Trees growing in grass have the slowest increase in height and trunk diameter. Trees in bare soil grow next best, and trees with mulch over the root zone have the greatest rate of growth.

Many homeowners wonder how to get grass to grow beneath a tree, where it often is bare or patchy. “It’s better for both the grass and the tree if you don’t try,” said Spencer Campbell ...