And it's not just rhododendrons, the award-winning estate near Truro also has an amazing display of early bluebells and some stunning yellow magnolias.
Whilst rain during the budding season last summer helped this year's flowers, Head Gardener, Gary Long, explained that a decision to remove or lower the height of much of the garden's laurel hedging has also done much to increase the amount of vibrant blooms by letting sunlight into previously shaded areas.
"We are seeing plants that have rarely flowered, or at best sparsely flowered, come into glorious full bloom this year," he said. "Every day we find new plants in flower. By reducing internal hedges in height throughout the garden, sometimes removing them completely, we have opened up vistas and views to plants that simply didn't exist 12-18 months ago.
"Last year's wet June and July suited our rhododendrons perfectly. In their native habitat they set their flower buds during the rainy season. That, coupled with the cold winter, means this season is amazing.
"The Royal Horticultural Society is using a rhododendron on the Chelsea Flower Show catalogue for the first time this year so we're forgetting it's the Chinese year of the rabbit/hare and at Trewithen we've classed it instead as the year of the Rhododendron."
The extra flowers rediscovered at Trewithen Garden this year include Rhododendron Niveum – Gary had believed there was only one in the garden and had been attempting to propagate more to guard against it dying out at Trewithen, but the hedge removal has revealed another three shrubs; Rhododendron Susan, which is so beautiful this year Gary has decided to enter it in shows, and a bright sunshine yellow Rhododendron Hotei, originally planted in the garden by the HRH the Queen Mother.
Trewithen Garden is currently open to the public every day from 10am to 4.30pm. For full details of opening times of the garden, the house and the café, as well as entry prices, please visit the website www.trewithengardens.co.uk