nope. they are somethimes fertilized with cow or chicken manure. Some vegans take issue with that and have created something called Veganic or Vegan Organic farming. Doubt you will find it in the supermarket.
This is just another example of what I put under the umbrella of Perfection is the enemy of good.
Just do the best you can. Remember that the definition of vegan takes that into account with the practical and possible clause.