1. Types of containers that work best
Nearly any pot will work for growing tomatoes in containers; as long as it has good drainage. Smaller containers tend to dry out very quickly in hot summer months. The smallest container for outdoor use is 8 to 12 inches in diameter. A 2-5 gallon container or 8-12” pots should be considered the minimum size needed for tomatoes.
In partial shade smaller containers can be used with more success. But understand tomatoes need room for healthy roots: at least 16 to 18 inches.
If you are planning to use recycled containers, scrub them well and rinse in a solution of 9 parts water to one part bleach. Containers that are porous such as unglazed clay, wood or cement, need to be soaked well in water before filling so they won’t pull the moisture out of the soil.
Roots are above ground in containers, they are more sensitive to temperature extremes. Midsummer heat can fry small feeder roots. Without these feeder roots, tomatoes will wilt even if the soil is wet. This forces larger roots to become susceptible to root rot fungus that can destroy the rest of the plant. Overheated soil is a common cause of tomato failure in container plantings.
Thick wood containers insulate best. Dark colored containers will absorb more heat and light colored containers reflect heat.
2. The best location for tomato containers
Select a sunny spot for tomatoes. They crave sun and heat, at least 6 hours of full sun is the minimum. 8 hours of sun is better. In hot climate zones, shade the containers during the afternoon for better results.
3. Soil preparation
Do not use garden soil! Garden soil may contain diseases and fungi and it is usually heavy and slow to drain. Buy a high quality container planting mix that has been sterilized, able to absorb moisture and drain quickly.
4. Feeding is important
Container plants can’t search for nutrients with their roots. Confined root systems demand frequent light fertilizing in summer. Nutrients are quickly leached from the soil with every watering and need to be replenished regularly. Begin applying a water-soluble fertilizer mixed half strength 2 to 4 weeks after planting. Continue to apply fertilizer every 2 to 3 weeks unless you supplement the soil with a slow release fertilizer.
Organic gardeners use liquid fish emulsion, liquid kelp, blood meal or bone meal.
Fertilizer packages will display 3 numbers that explain what the fertilizer is formulated to do. The numbers are always in the following order: (N) Nitrogen: for green leaves, (P) Phosphorus: for flowers and fruit, (K) Potassium: for root growth.
When one of the numbers is higher than the others, that indicates the fertilizer is designed to promote growth for that part of the plant.
Do not overfeed. A little is good, a lot is not better.
5. Watering container plants
Containers dry out quickly. Watering requirements will vary according to the season, type of container, soil mix and sun exposure. Check containers daily by sticking your finger into the top inch of soil. If it feels damp there is no immediate need to water. If it feels dry then water until some runs out the bottom of the container. In mid summer and on windy days this is a daily job.
In summer add a saucer that can retain water and be absorbed more slowly. In winter remove the saucer so the plants don’t sit in water. Water early in the morning to avoid wet leaves at night and mildew. Use a slow even spray to avoid washing out the soil.
6. Choosing tomato varieties for containers
Smaller varieties of tomatoes will grow more successfully in containers. Consider Balcony, Bushsteak, Cherry, Green Zebra, Marglobe, Roma, San Marzano, Stupice or small to medium sized beefsteak varieties.
Larger varieties can be grown in containers. But, they grow more successfully in 15 gallon or larger containers. Always read plant tags before purchasing to determine if the tomato variety is suited to your climate zone.
7. Seeds or Transplants?
Tomatoes are best purchased from transplants. Buy the smallest size available (6 packs if available). They will develop better roots. Larger size seedlings are not worth the extra cost.
If you choose to grow tomatoes from seeds there are several tricks to ensure better germination and plant growth.
• Start indoors to extend the growing season
• Plant seeds 2” apart and ¼ to ½ deep
• Keep the soil moist
• Move to larger pots when seedlings get secondary leaves