The Royal Free Charity has committed to maintaining gardens outside of the Pears Building, following concerns from a resident that plants are not being cared for.
Last month, scientists from the UCL Institute of Immunity and Transplantation (IIT) moved into the £60m new building.
The charity said plants are currently being watered manually as an outstanding part for the irrigation system has been delayed by "the current delivery issues affecting goods coming from Europe".
Linda Grove, who has led gardening projects with husband Malcolm outside the Royal Free Hospital for several years, said she is concerned the existing shrubbery is already dying.
The Belsize Park resident told the Ham&High: "It just looks a muddle and mess.
"It's all going to be weed very soon. They've spent masses of money on the building, but completely neglected the gardens.
"It was just a tick-box exercise, and it's already deteriorating."
The campaigner has found local businesses willing to sponsor a gardener to replant and maintain the grounds, and has received recommendations from a professional on what should be planted.
"Beautiful gardens are so important for mental health", she said.
"They make everybody feel better – the community, children, workers.
"I just want our local area to look good."
Royal Free Charity head of communications Eva Duffy said the gardens around the Pears Building are currently maintained by contractor Willmott Dixon, who built the Pears Building.
She said: "In late spring 2022, a new contractor will be brought in and we’re delighted that our team of volunteer gardeners, who already do a sterling job with the Royal Free Hospital gardens, will also play an important role."
She added: "We have been pleased to receive many positive comments from hospital staff, patients and residents about the new gardens.
"Although this is only their first season, many plants are already providing good coverage and attractive displays; others will naturally take a little more time to become established."
The charity, she said, has followed up with local businesses interested in sponsoring further plants to arrange either face-to-face meetings or telephone calls.
The existing landscaping includes shrubs and climbers, nine tree species and almost 40 varieties of ornamental plants, including asters, anemones, ferns, wild ginger, yarrow, carnations, euphorbia, lavender, geraniums and salvias.
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