Sat at the heart of the hospital in South Yorkshire, England, the courtyard can be used as everything from a quiet sanctuary to an area for play, performances or workshops.
The outdoor space originally featured colourful seating and planters, now complemented by Myerscough's designs, but its full potential had not been realised due to a lack of funding.
"The hospital had a new wing built but by the time they got to the courtyard, money had been allocated to, what at that time, were more essential interior spaces," Myerscough told Dezeen.
"We knew the value of these outside spaces in hospitals and what a difference we could make to patients, families, carers and staff if we could make a joyous space, a secret garden, that could be used all year round."
The updated courtyard now houses extensive planting, flooring mosaics, moveable furniture and a shelter called the Joy Pavilion that is finished with Myerscough's signature bright colours and patterns.
"I felt so strongly about the potential of this space and how much it needed to happen and hoped that it will assist in some way the wellbeing of the people in the hospital and who visit," added Myerscough. "It is so important to have colour and nature around you to lift your spirits."
The Joy Garden was designed by Myerscough pro-bono and realised in collaboration with cleaning product company Method with which she has recently worked on a limited edition collection.
Several local traders also collaborated on the project, helping keep costs down.
The size of the central pavilion was developed to allow it to comfortably host workshops and performances, without overwhelming the garden.
"[It is] big enough to have a workshop or performance but not too big if you are in there on your own," Myerscough explained.
It is constructed almost entirely out of wood, chosen to add warmth to the structure.
This includes its roof, which is covered in hand-cut wooden shingles, but excludes the metal flag poles and legs for the seating inside.
The Joy Garden is complete with new evergreen planting throughout, alongside scented perennials and bulbs that will change the look of the space in different seasons.
Myerscough's previous project at Sheffield Children's Hospital in 2017 saw her design the bedrooms and the entrance glazing to the new wing by Avanti Architects.
Similarly to the garden, her interiors for the hospital are full of her trademark bright colours and harlequin prints, designed to feel domestic and welcoming to young patients.
Other recent projects by Myerscough include the colourful reinterpretation of a Roman gatehouse on Hadrian's Wall in northern England and an installation of 105 flags on Oxford Street that aim to encourage conversation about renewable energy.
The photography is by Gareth Gardner.