Important: members must not bring grass clippings from lawns that have been treated with products containing Aminopyralid or Clopyralid herbicide in the previous year. Such products selectively kill broadleafed weeds that are growing in grass. Unfortunately these Aminopyralid and Clopyralid herbicides are persistent, and can kill plants that are later given compost made from grass that has been treated with them. Please either ask your lawn care company to confirm that their products don’t contain Aminopyralid or Clopyralid, or check on the RHS list of products, link 2 below.
Best of all, of course, go organic in your garden, and stop using weedkillers.