Summary: Partial green rebuilds replace only a portion of a golf green. The management problems caused by two different subsoils should be considered in relation to the cost to rebuild the entire green.
Well-intentioned superintendents try to save money on partial golf green rebuilds. They want to fix an unusual contour, or add some square footage to increase cupping area. The membership loves the idea, but they are shocked by the cost of green mix: processed sand, soil, compost soil that is installed 14″ deep on the green sub-grade.
To lower construction costs, the superintendent chops the most expensive item. The tee mix detail is modified to include only the area under the green rebuild. The existing tee mix remains untouched under the undisturbed part of the green. The old mix is full of thatch, with an outdated soil probably consisting of heavy, black soil or silty sand.
The construction budget will be reduced, but the reconstruction will cause a maintenance problem for the superintendent. Two different mixes create two different management requirements for one green.
I tell my clients to spend the extra money for a complete green mix replacement. This is a great time to remove all the old mix, install drainage piping if needed, and install new USGA spec green mix.
The existing grades can be copied with a skilled total-station survey technician. The existing sod can be numbered with chalk and re-installed in the same location as before (allow for some shrinkage). And the superintendent will have a uniform area of golf green mix to maintain, without any any complications. It will be cheaper in the long run.