Answer: Fortunately, it is not necessary to keep most vegetable varieties separated unless you are planning to save seed. (The major exception to this is sweet corn which should be separated by a huge distance from other corn.) Tomatoes in particular are self pollinated and so present very little risk of crossing. If they are being grown for seed they could be separated by alternate rows, or they can be carefully shaken and then the flowers covered with a bit of cheesecloth or a bag to exclude additional pollen. I hope this answers your question and I apologize it has taken us so long to respond.
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