Sand arrives at playgrounds already full of dirt - ours always had clay in it, which is terrible for drainage - only thing it would have grown was dirty clothes. .... If you want to grow in sandy medium, go to the hardware or home store and get a little bag of cactus soil. It does really drain! If it has to be sterile, spread in a pan and bake in the oven for say 3 hours at 300 degrees. ....... There are many plants that are commonly only grown vegetatively (and others that ought to be!) I get mad at the supermarkets' only selling "mint" - they can't be bothered with peppermint vs. spearmint, and yet the flavors are vastly different. It turns out it's not economical to spend the time planting and nurturing cuttings. Mints don't come true from seed, but growers insist on using seed and then just sell generic "mint" as though their customers are clueless. ..... I do think the suggestion to use potting mix is good - it's formulated to be kind to tiny roots - just be careful not to get it wringing wet. You can tell by its color whether you need to water yet or not. And you may yet succeed in making a new plant. I've done the impossible sometimes in my life without knowing it was impossible. (On the other hand, I've finally quit beating my head against the wall of difficult seeds, since it turns out there are other parts of horticulture were I can actually get something done. I buy my rosemary and bay plants, but grow basil and chives myself, and many flowers. And I propagate my own peppermint, thank you.)