A children's book about a plant or bush thrown into neighbours' garden and begins to turn gold then grow gemstones

As in the title. It was standalone, hard cover (my copy anyway), most likely English or British. Beautiful colourful illustrations. I would have had it in the 1980s.

Involved neighbours who hated each other and threw back and forth over the garden wall an ugly plant or bush, then coveted it when it became gold and full of jewels in one of the neighbours' gardens.

I believe at the end it poisoned both gardens.

I thought it was called The Magic Rose Bush or something but that seems not quite right.