What would happen if I put a 1 kilogram of sugar in a plum tree?

38 or more years ago.

Adding sugar to soil will work, it consist complex carbohydrates and plants do need it.
Green plants use this sugar to make starch, proteins and fats.
But instead of adding sugar directly, you can add sugar dissolved in water to your plants, so that soil can absorb it in better manner.

When you say “in it”, you mean…?

When you say that you did do this thing 38 years ago, why?

What are you hoping to get that google will not explain, technically speaking? Do you think others have added a kilo of sugar to trees?

@joeschmo In the trunk touching the soil. I wanted to grow fruit in a tree that I don’t recall ever producing fruit. My question is more confession than asking for more info, but I would still like to know.

You may have given the tree a bit more nutrition, but more likely you attracted ants and other insects. You may have contributed to its demise.

Your horse would have come by and gorged upon the sugar block in the tree.

And what remained would be covered in ants.

Adding sugar is sort of an interesting question/idea (I’d be curious what a biologist would answer), but I imagine:

* Other faster-acting life-forms which already consume sugar (especially insects) will go at the sugar and remove most/all of it before it gets into the soil.

* What doesn’t get eaten will largely get washed away in rain.