I made several experiments with plants, and in my opinion, if the product is well done, I mean, a true Spiritus Vini, gently distilled and perfectly rectified (caput, corpus, & cauda draconis removed), and a good quality plant, you don't need to bother with salts, insoluble salts etc, unless you want to make a vegetable stone.
Effects can be more than surprising.
What do you want to add with ashes ? They contain nothing of the plant now, they are burned ! No energy remains, and energy can only be in the Sulphury part. Don't try to imitate an Alchemical process while doing Spageria. This is not the same thing.
Don't over complicate, just make a good job at first.
Another problem I have seen is in the so called 'ens' process. People use K2CO3, or potassium carbonate, but if you extract this salt, per se, you will have a golden Spiritus Vini. Which mean that, if you add a plant in the deliquescent alkaline water, you will spoil your Sulphur with another one that have nothing to do here...
Why using an alkaline salt if you are able to make a pure S.V ... why using K2CO3 upon easily extractible plants and not directly S.V ? I don't know, maybe in order to add a "moon" effect ? In this case, just link it to the moon once extracted. And don't dare to tell me that "the book said to do so ...".