Are you planning to grow beetroot? Any particular colour/variety?
Beetroot is a pretty easy crop to grow and it gets along with most other plants. BUT it does not grow well with tomatoes, climbing beans or mustard greens.
I have not been able to find a definitive answer as to why it is said these crops do not grow well together. I have read they can be detrimental to beetroot's growth.
Tomatoes and climbing beans can cast a lot of shade, while beetroot love full sun so this could be one reason. As far as mustard green go I am not sure.
So when you are planning out your garden for September, plan ahead to keep these enemies, apart.