Before adding any type of finish to wood you always want to start with a clean surface. Whether you are applying linseed oil to raw wood before you assemble your garden beds for the first time, or applying it to pre-existing beds out in the garden, you’ll want to make sure your surface is clean.
Applying boiled linseed oil is relatively easy. For wood that has not yet been assembled into garden beds, you can simply pour the linseed oil onto the wood and then wipe it off using a shop rag or other clean cloth.
If you are using a rag to apply the linseed oil, you shouldn’t have too much trouble with excess. If you are using the paint brush method, it’s good to follow the paintbrush with a shop rag to mop up any excess oil.