Containers for Tomatoes Almost any type of container, if it is large enough, can be used. Plastic, wood, clay, or metal pots, and even old pickle buckets will work. Of course, you do not want to reuse a container that held a substance toxic to plants or to people. If you are re-using last year’s containers, clean them with soap and water, and then disinfect them by soaking in a 10% bleach solution for 30 minutes. That will get rid of molds, bacteria, insect eggs, or soil organisms present.
The container you choose must have drainage holes in the bottom so excess water can drain out, or the tomato roots will rot and the plant will die. If needed, drill or punch a series of ¼ inch holes at the bottom outside edge.
Some of the ultra-small tomato varieties can do well in a tiny pot or even a cement block, but most tomato varieties will do best in a 5 gallon pot or larger. Small, cascading tomatoes can be grown in hanging baskets, but careful attention must be made for watering needs. Smaller size containers dry out quickly, and may need watering two or more times on a hot day. The additional water will leach out nutrients faster from the soil, and additional fertilization may be needed.
The bigger the pot, the better. With roots over 6 feet long on some of the larger varieties, tomatoes need all the soil space you can give them. If you use a larger pot and provide more soil, the plants will grow bigger and produce more. A larger pot size will keep the soil from drying out too quickly in summer heat. If you will need to move a heavy pot around, purchase container dollies with wheels. Expect to plant just one tomato per pot. Your plants need the room and not the crowded competition.
Dark colored containers heat up quickly and increase soil temperatures that may harm delicate roots. Grow bags work well, but are porous and need frequent watering. Some pots made from porous materials like clay, concrete, or wood will dry out more quickly than plastic containers and will require more frequent watering. The British grow most of their tomatoes in large plastic bags. Coarse gravel can be used at the base of the pot to provide more drainage and to provide a counterweight to a taller tomato plant. Some people use wire mesh or even coffee filters to line the base of pots to keep soil from leaking out. Larger Styrofoam pieces can be used to lighten the pot; however, some Styrofoam peanuts are now biodegradable and will collapse as the season progresses.
Soil for Container Tomatoes Re-using potting mix is not a good idea. You will only be recycling last year’s molds, fungus, insect eggs, and weed seeds. Used potting mix can be nutrient deficient and compacted, but can be dumped into your compost pile for disposal. Plain garden soil is just too heavy for container planting; it tends to compress badly, decreasing air and water infiltration. Tomatoes in containers need a light and fluffy, well-draining but water retentive potting mix for the best root growth and aeration. You may use a commercial soil-less potting mix. Note that potting mix is not the same as potting soil. Potting soil is a mix of soil and other ingredients; potting soil compresses too much for containers. Mixes often include sphagnum peat or coir, perlite, vermiculite, compost, a small amount of slow release fertilizer and lime. Up to a third of the volume of a potting mix may be amended by the gardener with good quality compost for the slow release of nutrients. Do not buy a poor quality garden mix that may not drain well. Check the label for a list of ingredients and amount of fertilizer present, if any. Some gardeners prefer to make their own mix of peat moss, compost, vermiculite, sharp sand, and fertilizer. One good mix for tomatoes has equal parts of commercial potting soil, perlite, sphagnum peat moss, and compost. Add slow release fertilizer and lime, following package recommendations, to homemade mixes. Adding up to 10% of the mix volume with sharp builder’s sand will add weight to the soil-less mixes. Mix and moisten the ingredients thoroughly before use. Other good recipes for potting mixes are present at various state university web sites (Homemade Potting Media, Penn State Extension, https://extension.psu.edu/homemade-potting-media) (Soil for Containers, University of Maryland Extension, https://extension.umd.edu/hgic/plants/soil-containers).
Sun and Wind. Tomatoes need at least 8 hours of sunlight per day to do well. Check the amount of light carefully; it can change during the day or during the season. Some gardeners place reflective foil around the base of the plants to increase the light intensity. Tomatoes love heat, but if temperatures fall below 55°F degrees, or if daytime temperatures rise above 100°F, they will fail to set fruit. Protect pots from very high heat reflected from pavement. Full sun can overheat black containers and result in serious root damage. Some gardeners will drape their black pots with a light colored fabric to reduce heating. Pots can also be moved to a cooler spot during the heat of the day. Site the containers in an area protected from wind. However, good ventilation is important, and pots should be spaced so that there is room for you to move around them. Crowded pots increase the humidity level and encourage disease development. Put your plants nearby, so it is convenient to water and care for them.
Variety and Seedling Selection If the pot is large enough, you can grow any variety of tomatoes in a pot. Determinate types of tomatoes tend to be smaller (up to 4’) and suitable for containers. The determinate tomatoes grow to a certain height, flower, and produce a crop over a short period of time. Production may be the same or more than the larger indeterminate varieties, but the production will occur in a short time frame. Indeterminate tomatoes keep growing, flowering, and producing all season until frost. Indeterminate tomatoes are sprawling and will need support. Bury 7 foot stakes at least 1 foot deep or use large wire cages around the indeterminate varieties at planting time. Indeterminate tomatoes in pots are often pruned (by pinching out the suckers-small shoots in the leaf crotches) to 2-4 main stems for easier management of the plants; the number of fruit will be less, but the size of the tomatoes will be larger. Determinate tomatoes should not be pruned. Caged tomatoes need not be pruned. Some shorter, determinate varieties may also need support for a heavy fruit load. Loosely tie the stems to their supports. Some cherry tomatoes are dwarf in stature, but many cherry tomato varieties are actually monster plants and will need support. If possible, choose a disease resistant tomato variety. Heirloom tomatoes are not very disease resistant and production is often less than hybrid varieties, but their flavors are fantastic. Choose tomato varieties that will ripen before frost; any variety with days to maturity (the time between transplant and first fruit) less than 90 days is best.
Planting Your Tomatoes: Choose healthy plants that are about 6-8 inches tall and stocky, not lanky. The roots should be light, creamy colored and not crowded in the container. Plants already producing fruit or flowers seldom produce before other plants, and the plants seldom grow much larger. Before planting, make sure to harden off your plants for a few days. This toughens up and conditions the plants ensuring better growth once planted. Sudden exposure to sun and wind can kill a tender young plant. For 7-10 days before planting, set the young seedlings outside in a protected area. Each day, expose them to more and more direct sun. You will need to check the water in those small pots often. Withhold fertilizer. Protect them at night. After all danger of frost has passed and the soil has warmed to at least 50 degrees, you can plant. When planting, remove the lower leaves of the tomato and bury the stems deeply. New roots will form all along the stems. If using peat pots, bury the entire pot entirely; otherwise water will wick from the soil and evaporate from the exposed portions of the pot. Provide a cup of starter fertilizer solution around the plant, diluted according to packaging instructions, to give it a boost helping it get established. Shade the plants lightly for a few days to protect them. Label each variety with the name and planting date, so that you can grow the same outstanding variety next year.
Watering Your Container Be sure to water your container plants at the base of the plants. Use a soft stream to water the roots, not the leaves. Soil-borne diseases can splash up onto the leaves if you water vigorously. Water early in the day so leaves can dry out and reduce the possibility of leaf disease. Hot water from a sun baked hose can injure fine tomato roots. Be sure to soak the root ball thoroughly, and stop watering when some water starts coming out from the bottom of the pot; one deep soaking is better than several light soakings. The soil must never dry out, but it should not become soggy either. Every day, monitor the moistness and watering needs by sticking your finger 2 or 3 inches into the soil. Wait a few weeks until the weather and soil have become thoroughly warm, and then apply a 2 or 3 inch layer of organic mulch around the plant to conserve moisture, moderate soil temperature, and prevent the growth of any weed seeds. A few sheets of newsprint may be placed around the plant and then covered with an attractive mulch. As the mulch decomposes, it adds nutrients and organic material to the soil. Plants will need more water as they mature. You may find that the pots need daily or twice daily watering during hot, dry, windy periods. Water is extremely important, especially when the plants are blooming and producing fruit. A drip irrigation system is ideal. Too much water will starve the roots of oxygen and cause root rot; too little water stresses the plants; uneven watering can result in blossom end rot -- a black, leathery discoloration of the fruit. Plants may never recover from bad watering and production will decrease. Keep those roots happy by good watering.
Fertilizing Tomatoes require a lot of nutrients. Nutrients tend to leach out of containers with watering, and need to be replaced. Check the label of your potting mix; many mixes come with about a two week fertilizer supply, then the plants need to be fed or growth begins to slow down. Mix a timed-release pelleted fertilizer into the top of the soil mix, based on the package recommendations. Two weeks later, start watering with a balanced soluble organic or inorganic fertilizer to supplement the timed release fertilizer. The fertilizer solution may be applied following package directions every two or three two weeks, or diluted to apply more frequently. Observe the color of your tomato leaves; a fading from dark green to a lighter color can indicate a need for fertilization. Avoid high nitrogen fertilizer, which will encourage lush leaf growth at the expense of fruiting. Seaweed-based fertilizer, other organically based fertilizers, and micronutrient mixes have been shown to provide essential trace elements to the mix. Later in the season, apply more time-release fertilizer granules based on the manufacturer’s recommendations. Don’t exceed recommended amounts of fertilizer; too much can damage the tender roots. If you see scorched leaf edges on your tomato, you may be over fertilizing. Flush out the excess fertilizer salts by watering with a water volume 3 times the container volume.
Additional Care: Scout for water, fertilizer, disease, and insect problems on a daily basis. Correct the problem as soon as possible. Tomatoes self-pollinate within their flowers; a gentle, daily tapping of the flower stems should help release pollen and increase fruit numbers. The single most important ingredient for success is TENDER LOVING CARE, because your container tomato plants have to depend entirely on YOU for all of their needs.
Happy Gardening, Joe Baltrukonis