You can add an established Group of seeds to a collection or remove a Group from a collection using  that Group's management page. 

On this page

Add a Group to a collection 

Remove a Group from a collection 

Add a Group to a collection

You can share groups of seeds to more than one collection from the Group's management page by adding collections to that group.  

1. Click the Add Collections button
2. Click the checkbox next to the collection(s) in which you'd like that Group of seeds to appear 
3. Click the Add button

Remove Group from a collection 

Click on the checkbox next to the collection(s) you would like to remove and then click Remove Collection