You should be able to purchase smaller bags of potting mix. They actually sell a seed starting mix here in the USA in small bags. You could always add the left over mix to other potted plants in your garden. You can use it for established potted plants, just not for seed starting once the bag has been opened.
You make me smile because of your wonder and excitement over every thing your daylilies are doing! I remember having those ah ha moments some years ago! I can imagine you becoming the daylily expert in Italy because of your watchful eye and fearless curiosity! I hope you get a bigger yard in the very near future so that you can add more and not be so restricted in your love of gardening!
