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Identify what the plant is attached to
The National Park Service describes how vegetation can attach to or penetrate masonry and how removal itself can damage the surface. Pulling a plant from a weak joint can bring material away with it. Leave work at roof level and removal methods to someone who can assess both the growth and the masonry.
Look at the surface after the growth is dealt with
A clean patch can conceal a deep joint or cracked brick. Ask how the provider will document the condition that was hidden and bring it back to you before additional repair. An estimate for clearing growth should distinguish any repointing or brick replacement that depends on that later finding.
Consider how the joint stayed damp
The crown detail, a nearby runoff path or an already open joint can each affect work at the top. The plant alone is not proof that the fireplace leaks. Ask which moisture and drainage details will be evaluated alongside the local masonry repair.