This work introduces a “hydrate seed solution”, a surfactant solution containing pre-constructed structure II (sII) hydrate crystals, for the rapid formation of hydrogen-enriched hydrocarbon mixed hydrates. We observed the instantaneous nucleation and fast growth of mixed gas hydrates for both CH4–H2 and C2H6–H2 mixtures with the cyclopentane (CP) hydrate seed. The CP hydrate seed, which is immiscible with water, dominantly induces the growth of CH4–H2 and C2H6–H2 mixed gas hydrates with thermodynamically favorable sI structure. However, the THF hydrate seed, which is miscible with water, induced the formation of seed-templated sII CH4–H2 or C2H6–H2 hydrate, and the overall reaction was much slower than the CP hydrate seed case. For the C2H6–H2 gas mixture, C2H6 molecules could not occupy the small cage of hydrates, but H2 mainly occupied the small cage. The THF hydrate seed provided a higher storage ratio of H2 than the CP hydrate seed because the seed-templated sII C2H6–H2 gas hydrates have a larger number of small cages than does the structure I (sI) hydrate. As the CP hydrate seed concentration decreased from 2.78 to 0.278 mol %, the growth of the mixed gas hydrates was extremely accelerated, and the overall conversion was completed within 1 h. The growth kinetics of hydrogen-enriched hydrocarbon mixed hydrates in the non-stirred system was much faster than that in prior agitation-applied studies. These findings suggest a way forward to an enhanced formation of hydrogen–natural gas clathrates for sustainable energy gas storage.