There are various biodegradable seedling mats, differentiating in price, and quality and material. One of the best biodegradable seedling mats are hemp mats, due to its high water retention capabilities, there are for example jute mats, which are very cheap, but cant retain any water, so overall, will be more costly taking into account the extended watering period.
Biodegradable Hemp Seedling mat:
biodegradable seedling mats