For the healthiest plants, make sure you have good growing conditions. For most vegetables, that means full sun (at least 6 hours of direct sun a day). If you have poor soil, amend it with lots of organic matter, such as compost.
Choose Plants Sensibly
Some plants, such as tomatoes, are naturally more susceptible to pest and disease problems than others. To reduce problems, look for disease-resistant varieties. (Disease resistance is usually mentioned in catalog listings, seed packets, and plant tags.)Feed Your Plants Naturally
In most soils, fertilizing your vegetables isn't necessary, but it will help them grow faster and give better crops. If you feed your plants, choose natural products. Well-rotted animal manure from plant-eating critters (rabbits, horses, sheep, chickens) is a great source. Or look for prepackaged organic materials online or at your local garden center.
Note: If you have rich soil already, you may be best off not fertilizing. Too much of a good thing can make your plants put on lots of lush, soft growth that's loved by pests. Slower-growing plants often resist insects and disease better.Practice Rotation
If you plant the same vegetables in the same spot every year, disease can build up and be ready before your plants have much of a chance. Keep the element of surprise against your disease foes and try to plant your crops in different parts of the garden each year.
Because many closely related plants are affected by the same diseases, avoid planting them where their relatives were the year or two before. Two of the biggest families are the tomato family (tomatoes, peppers, potatoes, eggplant) and the squash family (squash, pumpkin, cucumber, watermelon).