ACCA accountant Katie Blake has become the firm's first director of finance, administration and human resources, following several years working for both blue chip companies and SMEs, including PricewaterhouseCoopers.
Wyer, who became chief executive after business partner and co-founder Chris Bowles stepped down in July, said Blake's work had previously been split between senior members of the business but that the company had now expanded to an extent that it needed somebody to head a new department.
There are now 37 staff at the £5.5 million-turnover landscape architecture, garden design and landscape construction firm.
Mark Latchford has also joined as a designer and Max Harriman as a junior designer, replacing two part-time designers. Latchford comes from the Cool Gardens company where he worked as design director, while Harriman joins after graduating with a distinction as a garden designer at the London College of Garden Design.
Wyer said there will be more change to come and to expect "some big announcements next year."
"We have been going through a process of strategic review for a while now and this is part of the restructuring. There will be more announcements in due course and we are strengthening our design and build and we are strengthening our design side.
"I am delighted to welcome three hugely talented individuals whose drive, experience and ambition will be invaluable to the company as we move into a new phase of development. It is particularly exciting to introduce some new, young talent to our flourishing design division. I have no doubt that they will become an indispensable part of the team."