Beardshaw will join current presenters Jim McColl, Carole Baxter, Carolyn Spray and George Anderson. He replaces Lesley Watson.
He said: "I have long admired the honesty and warmth that comes across in Beechgrove so to be invited to be an integral part of the team is a real pleasure.
"I am already involved in the planning stages and am now really looking forward to getting into the garden and helping to play a part in the continued development of Beechgrove, as well as explore some interesting gardens and meet with fellow plantsmen."
The BBC Scotland gardening programme, which has been on-air north of the border for 35 years, will continue to be shown on BBC Scotland, but will now also be seen on BBC Two this spring on Sunday mornings.
Producer Gwyneth Hardy, from Tern Television, makers of The Beechgrove Garden said: "Chris is a horticultural heavy weight with a lightness of touch that makes what he says accessible to all. He is a passionate expert with a wide ranging skill base who is not afraid of getting his hands dirty and as such will be a complementary addition to the Beechgrove team."