DavidN

Hi Marke2020
I'm surprised no one from your location has responded to this request.

Personally I haven't really heard of a Japanese Ash Bonsai. If you had a digital photo of it then you could post it here for us to possibly identify. If they are like normal Desert ash in Australia then there are very hardy trees.

I don't know what your weather conditions are like but your bonsai is still a tree and trees live outside, especially if you are in your warmer months. You really only have to worry if your temperatures go below freezing and I doubt it goes below 0 in England in spring.

Watering is probably the most important thing to get right with bonsai. Water only when the tree needs it. You can use a wooden chop stick to press down into the soil to the bottom of the pot and then pull it out. If the chop stick comes out wet and muddy, obvious you don't need to water. If it is dry then you water it well. You can always use your finger and press it down into the soil to check if it needs water in the same way.

Feeding, you would be safe with a liquid fertailzer, half stregth, every 2nd week in the growing season.

Your best bet would be to find a local bonsai club and join. They are invaluable if you find a good one. Also visit bonsaitalk and read as much as you can.

Best of luck
David