You can install KDE software (either the KDE4 Software Collection, or KDE Frameworks 5 -- but not yet KDE Plasma or KDE Applications) from both packages and ports. It's a lot faster to install from packages, and compiling KDE software will also take a lot of disk space and memory.
Packages are available from the official FreeBSD package repository.
x11/kde4, but there are also dependent ports for the larger components such as
x11/kf5-frameworks, but each individual framework can be installed separately.
To install KDE packages on supported FreeBSD versions (10.3 and later, and generally x64):
# pkg install x11/kde4 # For KDE4 # pkg install x11/kf5-frameworks # For KDE Frameworks 5