How Close to Plant Roma Tomatoes in Containers

Also known as plum tomatoes, Roma tomatoes (Lycopersicon esculentum) are popular for their low water content, which makes them the perfect option for sauce-making. Grown as an annual throughout the United States, Roma tomatoes are identifiable by their oblong shape and, while they are known for making sauces, many Roma varieties also make good slicing tomatoes for topping salads and pastas.

All tomatoes, including Roma varieties, fall into one of two categories: determinate or indeterminate.

Indeterminate varieties continue to grow vines and produce fruit for as long as weather conditions are favorable, until the first freeze. For gardeners who want continuous fruit throughout the growing season, indeterminate varieties can be a good option. However, because they grow continuously -- easily to 6 feet or more -- these varieties are not recommended for containers.

Determinate tomatoes only grow to a certain size, generally to 3 or 4 feet tall, regardless of favorable weather conditions. All fruits mature in a short period of time, so determinate varieties are often favored by those who can tomatoes or sauces. Because determinate varieties are more compact -- so they don't require large supports -- they are the best option for containers. To get continuous tomato harvests from determinate varieties, plant the first tomatoes at the beginning of the season, then plant a second set one month later.

The classic Roma tomato (Lycopersicon esculentum, 'Roma') is a determinate tomato suitable for container growing.

Select a large container for growing Romas, nothing smaller than a container with 20- to 22-inch diameter, which offers enough room for one plant. Larger containers can be be used to hold more than one tomato plant using the standard spacing for tomatoes. Tomato plants must have room to be spaced 24 inches apart for enough room for roots and proper air circulation around plants. To leave room for roots, tomatoes should not be planted any closer than 12 inches from the edge of the container. To fit two Roma plants in one round container, the diameter of the pot should be no less than 48 inches. This allows for plants to be placed 12 inches from each side and allows 24 inches between plants. Select deep containers that hold at least 4 to 5 gallons of soil per tomato plant to give roots plenty of room.

Suitable container materials include plastic, ceramic, terra cotta and wood. Do not use containers that have stored chemicals or treated wood because chemicals can leech out into the soil. Make sure containers have suitable drainage with at least four holes at the bottom.

Fill the container with high quality potting mix, which should offer the slightly acidic soil pH required for tomatoes -- 6.2 to 6.8. To make sure the soil acidity is right, use an at-home test. For container soil that is too acidic, raise pH by one point by adding 8 ounces of lime per square yard. For soil that is too alkaline, lower pH by one point by adding 1.2 ounces of sulfur per square yard. Mix the lime or sulfur into the soil thoroughly.

Before planting, work a slow-release 10-10-10 fertilizer into the soil at a rate of 1/2 tablespoon of fertilizer per gallon of soil.

Once the soil reaches 60 degrees Fahrenheit in spring, plant tomatoes. Dig a hole twice the size of the root ball and deep enough that the surface of the soil is even with the top of the root ball. Place the plant in the hole and backfill with potting mix. Water thoroughly, soaking the soil, after planting. Place the container in full sun, a space that gets at least 8 hours of sunlight a day.

Containers dry out faster than in-ground gardens, so check the soil every day. Water any time the soil is dry 1 inch below the soil's surface.