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Am about to put up a new greenhouse on a base of railway sleepers.  I have a long plastic planting trough that is about 1.5 feet deep and would take up one whole side of the greenhouse.   Because of it's height, it would bring the level of the soil above the sleepers.

Apart from the fact that I may need to water more often, ( and fertilize/renew  the soil in the pot )  are there any other advantages or disadvantages of growing greenhouse veg in pots as opposed to straight in the ground that I might not have thought of?

I was planning on growing tomatoes, melons, squash ... maybe a grapevine...

Apart from the grape, I almost always use large pots with most of the base removed for tom's and the like. I then sink them in the borders with an inch showing. This way it's easier to get rid of all the old compost. Direct planting would mean replacing your soil/compost in the borders to prevent disease build-up.