Up to 80% of their environmental impact is caused in the washer and dryer. Use an energy and water efficient washing machine. Look for the EnergyStar symbol.
Use environmentally friendly detergents, preferably phosphate-free.
Skip the fabric softener.
Only wash full loads.
When possible, don’t use your dryer. Line dry instead. More work, yes, but it extends the life of your clothes, and the planet.
Organic clothes are biodegradable. If you have a garden, compost them. You’ll make your plants happy.