How Big Do Tomato Plant Roots Get?

Container Plants

• The length and width of roots on plants grown in containers will be restricted by the size of the container. For example, roots on plants grown in a pot that is 18 inches deep will grow as deep as they can, then start weaving and wrapping around the sides of the pot and working their way upward, looking for water. One single root branch can grow from 2 to 2 1/2 feet long. This is why it is best to plant tomatoes in as deep a pot as you can get. If you are not concerned about the aesthetics of the pot, you can even use a large plastic or metal trash container to serve as the pot for the tomato plant.

In-Ground Garden Plants

• Even when the plant you are seeing on the surface is only a few inches tall, there is a lot of growth activity going on in the soil underneath. During the first stage of root development, called the "taproot," the roots grow downward into the soil, and can reach a depth of 22 inches in the first three weeks. The roots will also spread and branch out laterally. In the top 6 inches of soil, they can spread about 1 foot in width. By the time the plant matures, in four to six weeks, the roots underground can reach a depth of 3 1/2 feet. This is why it is important to space tomato plants at least 1 1/2 feet apart so they have adequate room in the soil for the roots to grow deep and spread horizontally.

Trench-Grown Plants

• The trench planting technique is used to train the roots of the tomato plant to spread and grow laterally. This is quite okay to do, because tomato plant roots grow laterally naturally. Roots will spread horizontally about 3 1/2 feet at maturity, and reach a depth of up to 2 1/2 feet (the reverse of planting tomatoes "vertically"). Instead of digging a hole, gardeners dig a horizontal trench in the soil. Then they lay the plant seedling at a 45-degree angle in the trench and cover the plant stem with soil up to the top two or three leaves. The roots sprout from the plant stem that is buried into the soil.

Raised-Bed Plant Roots

• A raised bed enables a gardener to give tomato plants a healthy start to produce strong roots. Raised beds are easier for gardeners to access to amend the soil with compost, manure, lime and fertilizers in comparison to digging flat soil and making amendments. Raised beds can also be used for the trench technique to grow lateral root systems. However, a raised bed will not alter the depth or span of the tomato plant roots. The tomato plants will still reach a mature depth of 2 1/2 feet and a lateral width of up to 1 1/2 feet per plant.