Thanks for the great question.

Over my years as a gardener, I have heard countless and conflicting opinions on the use of coffee grounds.

1), Coffee grounds contain nitrogen, phosphorus, potassium and other nutrients plants need. These can be in varying amounts depending upon source of the grounds. For this reason there is no set formula for knowing how much to add to a specific garden.

2). Besides these nutrients, coffee grounds may contain compounds that imparted flavor to the coffee. Sometimes these flavor amendments can inhibit plant growth. In short, depending upon the type of coffee grounds highly variable results could be observed.

3), Caffeine has been proven to have allelopathic effects upon other plants. These may be either beneficial (growth promoting) or harmful (inhibition of plant growth and/or seed germination) effects depending upon the other plant species.

Bottom line: depending upon the quantity of grounds added, the type of coffee grounds, and the plants in the garden to which grounds are being add, be prepared for variable results. Here is where experience and constant experimentation will be necessary. Maybe you will experience acceptable results or maybe you will not. At some point the decision may be made that is far easier to employ other means by which to enhance the fertility and nature of garden soil

See:

https://www.hunker.com/12405954/coffee-as-a-repellent

https://www.theguardian.com/lifeandstyle/2016/oct/23/coffee-grounds-are-not-good-for-plants-its-a-myth

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/will-caffeine-affect-plant-growth.htm - :~:text=Caffeine, a chemical stimulant, increases,be toxic to some plants.

https://link.springer.com/article/10.1007/BF00987675

Have fun and good gardening!!