Keeping weeds down in growing Trees in pots

[arminius]

I planted 500 Evergreen plugs into these 5 gallon pots last year. I had to weed them all 3 times last Summer. Each times takes hours to do. I tried layer of wood chips on top but weeds went right through that. Any tips? I plan on keep them in these pots for another 2 years. thank you

 

[Chuck]

Permeable weed fabric with mulch on top

 

[Oliver Buckle]

Loose mulch and an onion hoe.

 

[cpp gardener]

Try a pre-emergent herbicide. Most of them kill seeds or small seedlings and don't affect larger woody plants.