I wouldn't occur to me to use boxes as plant containers. They'd become a soggy mess in a couple of days. Unless, of course, there is some method of waterproofing them (inside and out) that I don't know about. Have your co-worker elaborate for us!

I guess as long as you don't overwater and they are in the sun they might dry quickly enough to be ok. But you'd definately be better off with lining it. Otherwise I don't see why it wouldn't work.

My experience with cardboard boxes is that you had to line them with black plastic trashbags for them to be useful, unless you had them outside where you didn't care if they melted or not. The problem then became that you had to be extremely careful with watering, or the bottom of the box just wound up full of smelly mud, just sitting there, and your plants weren't particularly happy. Also, if you had the box inside, your watering problems were typically compounded by less than an ideal amount of light.

You can do it, it's just tricky if you need to contain the soil and therefore have to line the box with plastic, because there's no drainage. I never had that great of a result when I did it, but then again, I tend to be an over-waterer who's in love with clay pots.

Verdant Croft