Tennant was plugging the latest Dr Who episode "The Watwers of Mars" on Graham Norton's chat show, which the BBC filmed at the Carmarthenshire garden.
Tennant said: "If you live anywhere near the garden you should go and visit — it is absolutely amazing."
The latest Dr Who episode, featuring the garden's great glasshouse, will be shown on BBC1 on Sunday 15 November at 7pm.
Click here to see the clip from The Graham Norton Show.
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