Answer
Do I need a garden designer and a landscaper, or can one firm do both?
One firm can do both, which keeps the design and the build accountable to one team.
In short
One firm can do both. A design-and-build firm draws the garden and then builds it, so the people who designed it are accountable for delivering it, nothing is lost in handover, and there is one point of contact. The alternative is a design-only designer who hands the drawings to a separate landscaper, which works if you already have a builder you trust.
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