White Edges On Cucumber Plants

Question

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Answer 1

It could be that it is lacking nutrients, mainly nitrogen, from being root bound. These should be moved to a new container, or moved outdoors and transplanted.

https://www.gardeningknowhow.com/edible/vegetables/cucumber/cucumbers-in-containers.htm

https://www.gardeningknowhow.com/edible/vegetables/cucumber/tips-for-growing-cucumbers.htm