I've heard of and seen many cabinet problems over the years, but bowing drawer bottoms has never been one.

1/4" ply dadoed into the box should hold anything you want without need for reinforcement. It's really really hard to get 70 lbs shoved into even a 36" drawer unless it's all cast iron. Storing all of your cast iron in a single drawer wouldn't be prudent. Split it up.

Thanks to you both. I could be over thinking this, but all the standard cliches are bouncing around my head: an ounce of prevention yada-yada, better safe than sorry, protecting one's investment, etc. It's an easy enough project for us to take on, so why the heck not?! :)

Our last house had really bad cabinets that did exactly what you fear-- the bottoms bowed and pulled the plywood bottoms out of the dados. It didn't help that the sides were assembled with butt joints and nails, so the corners failed as well. (Yours are not that bad!). My solution was to build new drawer boxes, which over time I did for all but the smallest drawers. Gluing a 1/2" piece of solid lumber across the bottoms of your larger drawers could certainly help stiffen them up. Probably not going to be a problem for drawers under ~22 in.

Thanks, rwiegand. We'll be getting to work, then, as I have only one stack under 22". ;)

Sorry I saw this a little late, but I have some wide and moderately deep drawers that have not bowed. I have one with lots of cast iron and another with lots of jars and bags of flour, sugar and liquids etc. They are both very heavily loaded. The larger drawer actually fell from insufficient anchoring of the rails, but again, the bottom did not bow. I just reattached the rails with more screws and all is well.

javiwa: good question; I probably shouldn't have posted originally as I didn't check and now see that my bottoms are ~3/4" melamine or similar and in addition are attached to metal drawer sides with ~3/4" bottom flange. They Are custom cabinets, but those metal sides look a little cheezy but they hold up great. I really had (and still have) that one drawer vastly over loaded.

Good to know, chas -- thanks again. 3/4" is hefty, I think, even if you're talking melamine/particle board (?).

Yes. Sorry, I should have been more clear. I am no expert on manufactured materials but am reasonably sure that melamine is much weaker than plywood. But I WAS attempting to indicate that the large thickness clearly overcame that weakness and in addition, the bottom was screwed to the metal side rails, preventing unlikely flex from occuring anyway.

Since, I'm still typing, I would like to point out that it is a big drawer; it is 33" by 22" so it can hold a lot of weight.

An easy fix would be to attach a piece of wood from side to side under the drawer...something maybe 2-1/2'' wide and the thickness of the lip on the bottom side. Spread wood glue on the reinforcing piece and the underside of the drawer and then use 3-4 countersunk screws going from the top side of the drawer bottom into the support piece. After the glue dries you won't have any worries.

Looking again at your pictures, I suspect you're going to be OK. Our drawers that failed had bottoms that weren't dadoed into the back of the drawer, instead they were slid into the the dados in the sides and front and then stapled to the bottom edge of the drawer backs. It looks like you have a dado all the way around that will fully support the bottom. I'd suggest just using them as they are and reinforcing only if/when you start to see signs of failure.