Planting into soil that was actually prepared

A lawn that is thin, mossy and full of weeds usually has a soil problem rather than a grass problem, and it is normally one of three: it is compacted, it is too acidic, or it is in shade that no sun-grass will ever tolerate. Adding seed to any of those produces one good month. Core aeration, a lime correction based on an actual soil test rather than a guess, and topdressing with compost address the first two; the third is solved by planting something else, because no cultivar makes turf grow under a mature Norway maple.

Planting has a regional constraint here that outweighs almost every design consideration: deer. Northern Westchester and Putnam carry heavy deer pressure, and an unprotected bed of hostas, arborvitae or yews is a feeding station. It is entirely possible to plant a beautiful property here — it just has to be planned around that from the start rather than defended afterwards.

And the planting itself: a hole two to three times the width of the root ball and no deeper than it, with the root flare left at or slightly above grade. Planting too deep is the single most common cause of a tree that quietly declines over five years, and it is invisible the day it goes in.