Janet Baraclough writes
The message
from "Dave" contains these words:

Just picked up my usual 5 growbags from local diy store and noticed
they are
thinner, ie: less volume. So I went around my local farms and
collected some
vitamin tubs that the farmers use for feeding cattle, called "cow
lick" or similar.
They are pretty big and a single grow bag barely fills 2 of them. My
question is
do I need to drill holes in these tubs?

Yes. Otherwise there will be stagnant water in the base, inviting
rot. Growbags also need a drainage hole spiked in them.

It is *possible* to grow things in deep tubs without drainage, but you
have to be very accurate about your watering, otherwise, as Janet says,
you'll get rot. The tub needs to be deep, so that the main root mass is
not in the area susceptible to waterlogging.

If you put them outside at any time, then you *will* need drainage
holes, as the weather is not as accurate at watering as you might be.

Problem with drainage holes in the base is that if you let the compost
get too dry, then it can be difficult to wet it again - the water runs
straight through. What I find works well for me is to put drainage holes
round the sides, about two inches up - then the bottom acts a reservoir.

Better still would be to fill the bottom two inches with stones or
crocks to discourage fine roots in that region - then you're getting
close to one of these fancy 'self watering pots' which have a separate
water reservoir in the base.

--
Kay