Place about 1” drainage material at the bottom of your container. Common drainage materials are sand, gravel and broken clay pot shards. Organically-minded gardeners have had success with corn cobs as drainage material. Other gardeners have successfully used shredded or balled newspaper or even Styrofoam peanuts as drainage materials in bottoms of containers.
Fill container three-quarters full with moistened soil. Throw in a handful of tomato fertilizer and mix it into the soil.
Remove seedling from nursery container. If the seedling has a strong root system or is root bound, you may need to squeeze sides of container to release the roots. Since you’ve moistened the plant, the soil and roots should pull away from container sides easily. If the root system is not as well developed, handle the root ball gently.
Loosen the roots. Gently spread apart matted roots at the base of the root ball. This will allow the plant to acclimate more quickly to the pot and spread its root system to fill the container.
Dig or create a small hole or depression in the center of the soil. Place the plant so the top of the root ball is just 1” below the container’s upper rim. It’s OK to bury part of the seedling’s stem – it will form roots underneath the soil and allow the plant to adapt to the pot quickly, especially in northern climates. In southern, humid climates, bury the stem less deeply as tomato plants tend to develop wilt more easily in humidity.
Plant just one tomato seedling per pot. Tomatoes have strong root systems. If they begin running out of space too soon, they’ll start flowering too early and then produce smaller fruit than optimum. When planting tomatoes in pots, give them room so they can max out their production.
Stake plant. Gently insert an appropriate-sized stake or cage next to the plant (except for basket tomatoes, which don’t need staking), about 2-3” from the base of the plant. Be careful to avoid puncturing the root ball with the stake or cage spikes. By introducing the stake or cage now rather when the plant is more fully grown, you’ll avoid disturbing the tomato’s root system later when it fills the container. (Check out different tomato cages to find the right ones for you and your garden)
Add extra soil to fill in around the hole and up to about 1” below the container rim. Press the soil firmly around the base of the plant.
Spread a light layer of mulch over container soil surface to reduce evaporation.
Water the container with a slow, gentle drip. Continue to water until there’s seepage from the drainage holes. Soil will settle during watering. If settling is significant, add a light layer of mulch to even out the surface. If possible, use a deck or drip irrigation kit for container gardening to ensure regular watering for your container plant.
Place the container in a protected location for a day or two to help the plant acclimate it its new home.
Set the pot in a place where it will get full sun and protection from wind. Check the soil daily during the first two weeks, while the tomato is becoming established. Keep your tomato evenly moist! ( Read more about watering tomatoes in pots.)
Keep records of tomato planting in pots, including the varieties you chose and the dates you planted them. That information will help you get off to a great start next season!
Video: Growing tomatoes in pots - how to plant tomatoes in containers