I group sweetcorn plantings together without harm and that makes it easier to chop up the residue, add compost like material, and plant a cover crop in late August [tillage radishes]. I don't have other large groups of vegetables except potatoes. Many crops fit in better in groupings because of plant height. or runnering.

Only watermelons and cantaloupes give me fits from diseases.

Many gardeners of old would group plant, Thomas Jefferson, George Washington for example, and would also interplant different flowers that either would help repel insect pests or attract beneficials and predators or both.

I plant 1/3 of what I have in space to the veggies each year and the other 2/3 to a cover crop. The next year, the veggies move to the formerly cover cropped area and the rest gets cover cropped. Don't have to worry about grouping each year that way and the soil is greatly improved by 2 successive years of rest with the cover as am I :) the only down side is I don't get as much ground in production as would be the case if it was all planted, I can live with that.

Crop rotating serves two purposes, desease prevention and soil improvement. To accomplish both objectives your rotation needs to fill certain needs (I know a couple, there are probably more). Where you grow a nitrogen user such as corn, need to follow with a nitrogen fixer such as beans. If I had the room, my rotation would be lagumes (beans, etc.) - Nightshades (tomatoes, eggplant, etc.) - leaf vegetables - other (corn, squash, melons, etc. In a particular year plant plot A with beans, followed the next year with corn, followed the following year with "other," followed with leaf vegetables, followed with nightshades; and then repeat. You can plant some beneficial flowers among the plots to attract beneficial insects and repell harmful ones.

When we are talking about gardens, even large ones, vs. fields I feel rotation doesn't matter that much when it comes to pests and diseases. I think rotation for nutrients is important if done right. However even within a family group the nutrient needs can vary. For instance, above and below ground brassicas have different needs and above and below ground nightshades do too.

For my main large crops I rotate them every year and augment the soil for that specific crop. For the secondary crops such as carrots, radishes, legumes, beets, lettuce, spinach, other greens, those go here and there in between the main groups. The main things I rotate are nightshades, onions, broccoli/cabbage, melons, squash, sweet potatoes, sweet corn. Once those crops are laid out I put in the lesser crops between them.
You cannot confuse insects like cabbage moths, potato bugs, cucumber beetles, squash bugs or squash vine borers by moving their target 50-100 feet away. They can find them no matter what! For diseases it may help but it depends on the disease and the soil. Fusarium is the most common disease and is in all soil so the way to conquer it is through improving the soil to what that plant wants, not by rotation.

For large gardens I recommend rotating the main groups around and then organizing the garden with harvesting in mind, also with irrigation needs in mind.

When an area does poorly I do a specific soil test on that spot and deal with it. I do cover crops but not over a whole season. I tend to go with lots of manure and then late summer legume cover crops wherever I can.

Yes you should group families. If it's bad to follow tomatoes with tomatoes, then it's almost as bad to follow tomatoes with potatoes. And of course, chard and beets are the same species as are celery and celeriac, so those go together. If you can figure it, a 5-yerar rotation would be better than 4, and a 6-year rotation better yet, and so on. The key is soil-borne diseases; they are as much family specific as species specific; think "co-evolution". Regards, Peter.

You may find this article of interest and help.

Here is a link that might be useful: companion planting