By Chuckwallah
United Kingdom 
I have a puzzle regarding a plum tree. It has been growing in my garden for about ten years and up until now I believed that it was the result of throwing rotten fruits from a wild plum tree (used for jam making) onto the flower beds just to see what would happen. This year it produced fruit for the first time but it is the wrong colour. Unlike the fruit that I believed it derived from, which was dark purple, this plum is a yellowish colour. It is possible that the tree did not come from the purple fruit that I scattered as we have thrown many things on to the garden out of curiosity, but I cannot recall ever seeing a yellow plum before, much less buying any. To add to the confusion these plums turn purple when they rot, which is happening quite a lot due to the weather and the dense clusters of fruit, so it wasn't until I risked trying one of the yellow ones that I realised that they were ripe.
Can anybody suggest what we might have here and what to do with them? A brief google search turned up the Mirabelle plum, does anybody know if these turn purple when they rot?
22 Aug, 2014
Answers
It's probable that the stone that grew came from a purple plum. Plums grown commercially are usually hybrids, so growing a plum from seed will not necessarily produce a tree that bears the same fruit as what you planted the stone from.
It's good that it grew, and to produce fruit is a bonus. Plum trees need to be pollinated by another plum tree of a different species. The other tree needs to be in the same pollination group, or an adjacent one (flowers at the same time). Your plum tree probably hasn't fruited before now because it wasn't cross-pollinated. This years success is probably due to a bee landing on a suitable tree somewhere before yours.
22 Aug, 2014
Just had Greengage jam on my morning toast. Better than any of the purple plums.
Only thing to be careful about is that if this is a seed grown tree and therefore on its own roots there is a distinct possibility, if not probability that it will sucker. You need to keep an eye out for plants coming up in various places as the tree grows.
Our Greengage is part of the hedge and there must be a dozen suckers coming up in the roadside verge.
22 Aug, 2014
There are golden plums apart from Greengages, but all delicious anyway.
What do do with them? Eat them! Whatever you do with purple ones will be just the same for golden ones.
22 Aug, 2014
Previous question
I have a golden gage......a greengage , its like a plum and bright yellow when ripe
you cannot ever tell what you will get with seeds, thats the fun!
22 Aug, 2014