The crystal mushrooms were very easy to produce en masse. Ed was nonetheless in no hurry. Planting all of them at once would be no different from killing himself.
'I need to isolate a small zone and try things out' The doom shroom had isolated itself after burning the mycelium, but that didn't mean the same thing would happen with the other elements.
Mushrooms grew in moist areas so they'd have some amount of resistance to the water element. Of course, if the place where they tried to grow was soaked most would still drown, but mushrooms were too broad a category. Ed had to narrow it down.
'Can I, a magic mushroom, survive the coursing of earth, wind, or water elements?' That was the question he had to ask himself as he had no element to speak of.
'Since fire burns me I do have weaknesses just as I have strengths, my best bet is water after all' To further guarantee things he could provide the spirit smith the smallest water crystal he could find.
