Home gardeners choose tomatoes as their favorite vegetable crop, according to the University of New Hampshire, while Colorado State University ranks basil as one of the backyard gardener's favorite herbs. Grow the two popular plants together and not only do you have the core ingredients for many popular recipes, but basil grown among tomatoes can also deter common tomato pests like hornworms, according to Cornell University.
Choose a gardening site. Both basil and tomato require full sunlight--a minimum of 6 hours of sunshine--for optimal growth, and both species also love well-drained soil.
Amend the garden site. Sir in 3 to 4 inches of aged compost to increase the soil's fertility and aeration, and also improve the soil's concentration of organic material. Follow the compost with a single application of an all-purpose 10-10-10 garden fertilizer, spread according to the fertilizer's labeled rate, because potency varies by product.
Plant the basil seeds 14 days after the last frost date in your area, according to Colorado State University. If you're unsure of when this date occurs, consult the Farmers' Almanac. (See Resources.) You should sow seeds 1/4 inch deep and space each plant in the row apart by 6 to 12 inches, according to the University of Minnesota.
Water the planting area twice daily or as needed to keep the soil moist. The University of Minnesota says the seeds will typically germinate within a week.
Plant the tomato seeds once the outdoor temperature is consistently above 60 degrees F, according to the University of New Hampshire. Arrange the row of tomato plants approximately 4 feet from the row of basil plants, running in a parallel direction. Bury each seed 1/2 inch below the soil surface. Separate each plant by 24 inches, according to North Carolina State University.
Mulch both plants as soon as the respective seedlings are 3 to 4 inches in height. Spread mulch in a 2-inch-deep layer. This helps conserve soil moisture, conditions the soil as the mulch material decomposes, and blocks weed growth.
Manage the basil plants. Water the plants once a week, applying enough moisture to moisten the ground to a depth of 6 to 8 inches. Pinch off the plant's flowers to encourage continuous growth of its pungent foliage. You should fertilize the plants a couple of months after planting with a 5-10-5 fertilizer, spread at a rate of 3 oz. for every 10 feet of the row, according to the University of Minnesota.
Manage the tomato plants. Water once daily with enough water to moisten the ground to a depth of 8 inches. Fertilize the plants with a basic 10-10-10 fertilizer at a rate of 3 tbsp. per plant as soon as the plant's first set of fruit appears, and every six weeks after that, according to North Carolina State University.