Let me start with an example of bad crop rotation (I do not always do as I preach ... :))
As you can see on the picture, the roots have bumps on them and are swollen. You can click on the picture to enlarge and see the details. These roots are tomato roots damaged by nematodes. Nematodes are a problem in Florida and they usually attack nightshade family of plants, such as tomatoes, peppers and eggplant.
One school of thought to remedy nematode problem is to "solarize" your soil, which involves covering the soil with plastic and let it sit in the heat of the summer, thus raising soil temperature to some 130 degrees and killing nematodes. I do not like this method because in addition to killing nematodes it will also kill beneficial insects and organisms that are much welcome in the garden, especially earth worms. If I were a fisherman, or fisherwoman, I could dig at least a shovel full of worms from my garden every day. And I like that! Earth worms make best manure because they eat and excrete plant matter, as well as dig furrows in the garden and aerate the soil.
So my answer to nematodes or other damaging pests is crop rotation. In a small garden crop rotation might be a challenging task. I have devised an "easy" plan to accomplish this.
First, divide vegetables that you plan to grow in three groups: Nightshade (tomatoes, peppers, eggplant and regular potatoes), Cover Crop (cowpeas, snap peas, beans) and Other (carrots, lettuce, broccoli, cabbage, okra, amaranth, radish, etc).
Second, draw your garden on a piece of paper and divide it in three parts, that's your master plan. I actually divide each bed into three parts, which takes care of dividing the whole garden. Then rotate your crop:
Fall | Nightshade | Cover Crop | Other |
Winter | Other | Other | Cover Crop |
Spring | Cover Crop | Nightshade | Other |
Summer | Other | Cover Crop | Cover Crop |
Fall | Cover Crop | Other | Nightshade |
Winter | Other | Cover Crop | Other |
Spring | Nightshade | Other | Cover Crop |
Summer | Cover Crop | Cover Crop | Other |
Pictured above is a 2 year rotation plan. As you can see, Nightshade family is not planted in the same space for a year and a half, which I think is a pretty reasonable time.
Since Nightshade family is most successible to pest damage, it is important to move it around; the rest of the vegetables, Other and Cover Crop are interchangeable: you can create your own rotation schedule with them freely depending on your vegetable needs.
In addition to crop rotation I always tuck flowers, especially Marigolds, and herbs in "Nightshade" and "Other" parts of the garden to provide bio-diversity and beauty to the garden, as well as attract beneficial insects.