sweetcorn and courgettes

They'd have to be mini courgettes, otherwise forget it. Corn is extremely greedy fnutrientwise and is a longstanding crop. Courgettes, another longstanding crop, create a rather large bush and we've all seen some of the 'baseball' or cricket bats that can happen if we happen to miss a few or are lax in picking. I can't imagine why GW would recommend this kind of planting as both varieties would suffer in the long run. You could plant courgettes at the end of the corn rows or blocks, but never in between.

iv planted my sweetcorn inbetween the courgettes and now can see iv made a mistake.My thinking was as space is so tight on my patch the corn goes up and the courgettes spread.I never gave thought to how greedy they are. 

In South America they have a planting system called the "Three Sisters" or "Holy Trinity", based on companion-planting of their three main food crops of Maize (Sweet Corn), Squashes (A Courgette is related to Squashes), and Common Beans (French/Kidney etc).

They dig/make a well fertilised square bed, and plant all three crops together (Corn first) as they don't directly compete and also support each other. The idea is the Corn supports the beans, the Beans add Nitrogen and the Squash suppresses weeds.

Bob

Sorry Bob

 

But the 3 sisters plantings are well spaced apart so everything has room, unlike our standard plantings of corn less than a foot apart. 3 sisters is closer to 2 ft apart, which few people have land to spare. A number of people on this forum have tried 3 sisters and most have been very unhappy with the results as there are other tricks to the system that are rarely mentioned, like planting a whole fish below each corn seed to act as fertilizer for all 3 plants. Not sure this is too practical for most lotty owners in both cost and keeping the hungry pests away.

I hope you are not having a trailing courgette in mind as well.