Submit. After the morel mushroom's spores come in contact with the right growing conditions, mycelium develop and mature into an adult morel mushroom within 15 days. Mature morels can live for up to two weeks before decomposing.Keywords: morel mushrooms, grow morels, mature morel.osh Duvauchelle is an editor and journalist with more than 10 years' experience. His work has appeared in various magazines, including Honolulu Magazine, which has more paid subscribers than any other magazine in Hawaii.