I am a Lion brand online retailer and a custom crochet company. I use only Lion brand yarns, unless asked for otherwise on custom orders. They have been on the market since 1878 and sell a variety of yarns, from 100% natural fibers including cotton, bamboo, alpaca and wool blends.
Cotton: Decomposes in about 5 months. When composted, it can decompose in a few weeks.
Wool: Biodegrades readily in as little as three to four months but the rate varies with soil, climate and wool characteristics. This fiber is composed of the natural protein keratin, which is similar to the protein that makes up human hair. When keratin is broken down naturally it does not pose any environmental hazard.
Bamboo: Biodegrades in about 3 years or within 6 months when composted. Bamboo itself can be a highly sustainable crop. While most bamboo fabrics on the market are a form of rayon where the manufacturing process is intensive and involves harmful chemicals, recent years have seen an improvement in how these chemicals are managed, which is a step in the right direction.
Hemp: The fabric can decompose in 2 weeks, has various natural advantages such as keeping you warm in winter, cool in summer and even protecting you from UV rays. Hemp also naturally reduces pests, so no pesticides are usually needed. Amazingly it also returns 60-70% of the nutrients it takes from the soil.
Jute Twine: This fiber can decompose in 1-2 years and can be composted. Jute is a natural fiber derived from the plants Corchorus Olitorius and Corchorus Capsularis.These plants are native to the indian subcontinent and grown throughout the year. The long, soft and shiny fibers are spun into coarse, strong threads that are used for many things.
The clothing that ends up in landfills can sit there for 200+ years, and as it decomposes, it emits methane—a greenhouse gas more potent than carbon. Much of what we donate gets packed, shipped, and re-sold overseas or gets dumped in landfills anyway. So why not use natural fibers and at least it will decompose much faster and we can even use some of these in our own compost!