Steriliseing soil

If you want the baskets to retain moisture, you can get seaweed-based moisture-retaining stuff that's presumably biodegradable. I have some, but I haven't tried it enough to be sure if it works or not. I guess I'll be adding it to my hanging baskets this year, though!

I think this is the stuff I bought, though it's out of stock at the moment:

https://www.organiccatalogue.com/product...00g_783184