Glyph origin or any mnemonic for 蕴?
蕴 means accumulate.
蕴 is merely a phonetic-semantic character comprising plants 艸 and 缊 which provides sound. 缊 is an obsolete character that means &quot;tangled strings&quot;. 缊 itself is silk and sound component  meaning kindness (giving a bowl 皿 of food to a prisoner 囚). None of these characters contribute any meaning to the definition of 蕴.
If you want a sort of mnemonic, I'd use 蕰 instead. 蕰 is one of a variant forms for 蕴. Mnemonics are more difficult to think of if the sound component 缊 isn't a common character. But with 温 (warm) being a more common character, you can think of it as gathering/accumulating vegetables 艸 to keep them warm before eating. Just remember that the standard form is 蕴 and not 蕰.
https://www.zdic.net/hans/%E8%95%B4