Last month I reported on our ongoing trial with growing tomatoes in containers. To recap briefly, we are growing three different tomato varieties in containers. Our goal is to learn about best practices for growing tomatoes in containers and to see if these three varieties are suitable for this method. The three varieties we chose all claim to be suitable, but we don't always trust the seed catalogs! They are Renee's Better Bush (a round slicing tomato), Inca Jewel (a paste or Roma type), and Prairie Fire (a grape tomato).
Our Field Test committee met recently to check in on our progress. Most of us reported our tomatoes growing quickly and in good health. So far, the weather hasn't been too hot, which has been a boon. We discussed strategies for hot summer weather, which is almost certain to hit us eventually. Most of us planted our tomatoes in large black plastic pots. This material attracts heat and doesn't have any insulation, so it will be hard on tomato roots confined in such a space. Several ideas were offered on ways to shield the pots from the direct sun. Painting them white should help, since white reflects heat, as opposed to black, which absorbs heat. Pots can be wrapped in insulating materials. They can be placed inside a slightly larger box, which will absorb heat and provide shade. You can place potted plants or other obstacles around them. In hot weather some shade can be helpful.
Your watering schedule should provide consistent moisture for the roots. Watering from the bottom is recommended, providing you have a large enough tray to put under the pot. If this is not possible, water from the top deeply enough that the water can drain out of the bottom. Some drooping of leaves in mid-afternoon is not cause for alarm. Water in the early morning or evening. Soil should be kept moist but not wet. One useful tool is a probe for detecting moisture levels. These are inexpensive and give you some peace of mind if you're unsure about when to water.
If your plants are getting tall, it's time to stake them. You can put a tomato cage over the plant with the feet buried inside the pot. If you place the plant against a wall or pole, you can tie the stake to that to add stability. Any structure that will stay firmly in place and can contain the growing stems will work. The corner of a gazebo is a great place for a plant. It's best to get the stakes in place early so you can gently tuck the new growth inside the horizontal constraints and keep them growing upward. Otherwise, they will grow sideways and be vulnerable to breakage. Prairie Fire is the one test plant that is semi-determinate, meaning a vining type that will continue to grow taller, so it is most in need of support. The other two are supposed to grow to about 3 feet, but they may need support as well. Better to be safe and provide support than to have the stems fall over and break off.
Whether and when to fertilize depends on your planting materials. An all-purpose planting mix will provide all the fertilizer you need at first, but as the plant grows and consumes the available nutrients you will have to add some food. A plant in the ground can send its roots down and out to search for more nutrients but a plant in a pot is limited to what you can provide. The potting soil bag probably specified some guidelines for when and how much to fertilize. When you do fertilize, choose an all-purpose balanced fertilizer. Monitor your plants carefully and be alert to changes in color or vigor.
Napa Master Gardeners are available to answer garden questions by email: mastergardeners@countyofnapa.org. or phone at 707-253-4143. Volunteers will get back to you after they research answers to your questions.
Visit our website: napamg.ucanr.edu to find answers to all of your horticultural questions.
Photo: Donna Woodward