Don had stepped down in 2008 after suffering a stroke but the show was accused of dumbing down with Buckland at the helm.
Buckland described his time on the show as "the best and worst of times".
He said: "Justifying the decisions of others is never easy and working all the hours God sends makes family time very hard to find.
"There is still a raw wind blowing through me. I go out in the garden and everything looks dead."
But Buckland says that he has been "deeply humbled" by goodwill messages from viewers.
He said: "I have always stuck up for ordinary gardeners and I have been so touched that so many have stuck up for me.
"At the end of the day, as a good friend said, it’s only telly.
"I will always have gardening and that’s what will get me through feeling so let-down and humiliated.
"At times like this, you just have to remember that what holds true in gardening also holds true in life.
"When things don’t go your way, try again. Winter doesn’t last forever."
He added: "The highlight has been meeting so many wonderful gardeners and the fans of the show, who during my time on Gardeners' World have inspired me with their love for their gardens and their heart-warming tales of their own trials and tribulations."
Buckland reveals his distress in the latest edition of Amateur Gardening magazine.
Alys Fowler, another Gardeners' World regular, has also been dropped by the BBC.
Carol Klein and Joe Swift will return for the new series alongside Rachel de Thame.
BBC commissioning editor Alison Kirkham said of the change: "I'm delighted to welcome Monty back and I really look forward to seeing him sharing his expertise in his own environment."