So, I have been buying fresh locally grown asparagus at the farmer's market for a few weeks and had an issue last week. I snapped the stems as usual. I immersed them in a large, container. Very little sand on the bottom. I continued to change the water until clean. Just to be sure, I rinsed each one individually under running water.
Then, lo and behold....gritty asparagus. Threw the whole batch out.
Any tricks to doing this? They really didn't look dirty.