These books about growing onions and tomato companion planting will provide you with a wealth of knowledge. Here are things you'll learn.

Ideal Growing Conditions:

The specific soil types, pH levels, and climate conditions best suited for growing onions and tomatoes together.
Planting Techniques:

Step-by-step guidance on how to plant onions and tomatoes, including spacing, depth, and the best times of the year to plant each.
Companion Planting Benefits:

How onions can deter pests that commonly affect tomatoes, such as aphids, due to their strong scent.
Nutrient Requirements:

Understanding the different nutrient needs of onions and tomatoes and how to balance fertilization to benefit both plants.
Watering Practices:

Best practices for watering to ensure both plants thrive without overwatering or underwatering.
Pest and Disease Management:

Identifying common pests and diseases that affect onions and tomatoes and how to manage them organically and effectively.
Crop Rotation:

How to rotate crops in your garden to prevent soil depletion and reduce the risk of diseases.
Harvesting Tips:

The signs that indicate when onions and tomatoes are ready to be harvested and the best techniques for picking them to avoid damage.
Storage Methods:

Proper methods for storing onions and tomatoes post-harvest to maximize their shelf life.
Companion Planting Layouts:

Garden layout ideas that optimize space and ensure both onions and tomatoes receive adequate sunlight and airflow.
These insights will help you create a productive and healthy garden, enhancing your yields and the quality of your produce!