I don't do a lot of container gardening because I'm terrible at it, but according the theory behind square foot gardening, 6" is all you need to plant anything. I guess that it works since people keep doing it and harvesting crops. Although I imagine there is something else involved in that method that allows it to be successful. You might look into what those guys do since you will be using a similar style.

Thanks Zach for guiding me to the proper forum.
I will post my query over there also.

Lettuces and herbs do well in shallow containers, not so sure about cucumber & melons though- I tried to grow zuchini, pumpkin, and cucumbers in 1x1x1 foot cedar planters and they did awful, while my friend's did great planted in the ground where their roots could spread out. I even had high quality potting soil mixed with compost for them to grow in, while hers were grown in only slightly amended clay soil. So container size can really affect plant size. I grow mostly greens now which are still a bit smaller than hers but do better in small containers than other things. Also not sure about using styrofoam, it's not very natural- though it takes forever to break down so may be just fine but I'd do some research before growing food in it.

Squash and melons have huge, deep root systems.

You could grow densely planted leafy green vegetables in them, like lettuce and leafy herbs. Harvest with scissors (give them a "haircut") and let them regrow, cut again.

I do all my veggies in containers. I don't think 5 inches would be good for any cucurbits. I've successfully grown sugar baby watermelon and cucumbers in 15-20 inch deep half whiskey barrels holding about 25 gallons of potting mix. If you're going to try growing them, I suggest you read about container soil in the container growing forum. You'll do much better if you don't use soil or compost in a container.

The heat over here wont work for lettuce and coriander. Its already past 80F during the day.

Yes, Ohio: I am also a active viewer of the Container Gardening forum and have learnt a lot from you all and esp. Al (Tapla). I use potting soil and mix in quite a lot of perlite (pine bark is not available here) and have had good tomato harvest. The plants are still going good and fruiting.

Since you are here, I was just wondering if I should cut back on the perlite for cucumber / melons because the heat over here is going to get intense. Expected to go past 100F in Mid May. Already my tomatoes are drying out on a daily basis (and its only 80F high at this time). A well draining soil may become a trouble for these cukes and melons? What is your advice? - I will not be able to tend to the plants early morning because of work / job commitments.

Saood: I'm sorry I didn't notice that it was you. I have seen your posts in the container forum and know you have been hard at work learning about what container plants need. If you were able to grow tomatoes in your conditions, you will be able to grow melons and cucumbers. They have similar needs to tomatoes, with maybe a little more demand for even moisture, especially early in their lives. If you have a container that is deep enough (at least a foot) and drains well, I think you could cut back on the perlite and maybe use a heavier mix that holds more moisture. You know that in the American south, many gardeners do not grow things like tomatoes and cucumbers in the summer months because of the heat. If your tomatoes are already showing stress from the heat, this may not be the best time to start melons, which can take three months to mature. Cucumbers grow a little faster, so they might be OK, and you may even have access to varieties that thrive in your climate.

I don't think that the height is the over riding factor except for maybe the fact that your in a very hot climate. On the other hand, total volume is important and you said you had about 7 gallons per container. That's plenty of dirt to grow cucumbers. Your roots will grow out instead of down. I did some last year in five gallon buckets and that worked well.

Thank you all for your input.

I think I will try out both ways. In a foot deep as well as 5 inch deep and compare the results. Hopefully this will become a good future reference.

Thanks.

I use Styrofoam boxes for growing some vegetables. When I want more soil depth I get two identical boxes, cut the bottom out of one and stack it on top of the other, basically doubling the depth and volume of the soil.

The top edge of the boxes needs to be flat (though maybe not if the sides were lined with plastic).

The stacked boxes can be stabilized with toothpicks or bamboo skewers, however it's not really necessary.

I have even made triple layer boxes.