What's eating my lettuce?
I really know almost nothing about growing vegetables in Colorado. I have a few things in whiskey barrels on my front patio. This year I tried lettuce and chard for the first time. The red leaf lettuce came up nicely and has since been absolutely shredded by something I can't see. It's just devoured almost completely. The same something seems to be nibbling some nearby basil and green lettuce, but seems particularly fond of the red leaf lettuce. It doesn't seem to be bothering the rainbow chard in the same barrel. Any idea what it might be or what I should do about it?
These are planted in a rich mixture; I have never used any fertilizer or insecticides on them.