There are many good companion plants for tomatoes, but how do you work them into an overall garden plan without just feeling like you're wasting valuable veggie-growing space? Here is an idea for getting the most use out of a popular tomato companion plant: borage.
Borage is a perfect companion plant for tomatoes because when planted nearby, it deters tomato hornworms -- a real pest for many tomato growers. Its bright blue flowers (which are shaped much like tomato blossoms) are a pretty addition to the garden as well.
You could just stop there, but why not add another crop and really get the most use out of the borage? Bumblebees and other pollinators adore borage blossoms. And, happily, borage blooms fairly steadily up until frost. So it makes sense to make use of all of those pollinators that the borage is attracting to your garden bed. A good idea would be to plant either summer or winter squash nearby.
So, here's how it works. The tomatoes do their tomato thing. Borage, planted near and in-between tomato plants, deter hornworms and attract pollinators for the squash you've planted.
An idea for a four foot by eight foot bed would be to plant a tomato plant in each corner of the bed, with a borage plant between each tomato plant. Then, in the center of the bed, plant two squash plants. They'll get plenty of sun there, and will be able to trail beneath the tomato plants. And everyone will be happy and healthy!