Summer is rolling into Kew Gardens, and the giant waterlilies are once again drawing the crowds, who come to marvel at their size. This year, Carlos and Lucy think they've discovered a new third species of giant waterlily previously unknown to science. We follow them as they gather the evidence, along with partners in Bolivia, to try and prove their discovery to the world, and also see how Brie handles the monster-sized lily pads, when they take over the Waterlily House. Aaron is looking at ways to replace coffee plants threatened with extinction by climate change, pests and disease. With the future of our favourite beverage in his hands, we follow Aaron from the labs at Kew to the plantations of Uganda, and onto a coffee roaster in Bristol to find the perfect new brew. The stakes are high: if Aaron fails, it could mean no more coffee for any of us. We also find out from garden and plant historian Advolly how Kew had previously helped with a Victorian coffee crisis, and how Kew's first plant collector of colour played an integral part in the story. Down at Kew's wild botanic garden Wakehurst, Katie and the tree gang have to deal with some invasive rhododendrons that are threatening the plant collection, and it'll require abseiling with chainsaws to get to those hard-to-reach places. But not all rhododendrons are so unwelcome, and Olivia shows us their world-beating collection. We then learn about the Kew course that attempts to change the face of 21st-century horticulture and meet some of the inaugural students. In the Palm House, Florence overcomes her fear of heights to do some pruning in the roof and, back at ground level, Steph is refreshing the Alpine House plants ready for this year's summer rush.

Dave tackles the massive dead-heading job that the roses bring to the gardens, while head of tree collections Kevin is contemplating another epic pruning job. It's all change in front of the Palm House, where, under a sweltering summer sun, the decorative team race to arrange thousands of new plants on the parterre, while Alberto is waiting on the flowering of the titan arum, which is always accompanied by the smell of rotten meat and an influx of curious visitors.