Container Gardening: Growing Tomatoes at High Altitude

Growing tomatoes to maturity in high altitude areas is challenging, but can be done. The biggest problems with any type of gardening at high altitudes are the short growing season and danger of frost on any night of the year. More minor problems to be considered are the danger of hail and drenching afternoon thunderstorms. The beauty of container gardening is the portability which allows a gardener to mitigate these problems. The key to success for growing tomatoes in containers is planting them in a large enough container to develop a strong root system, yet maintaining mobility so the plants can be easily moved when climatic conditions require a protected location.

What Tomatoes Need to Thrive

Tomatoes tend to be fragile and needy plants by nature. In order for them to mature and bear fruit, they need at least eight hours of sunlight per day, warm but not hot temperatures, and a longer growing season than is afforded in mile-high or higher locations. Most tomatoes require 70 to 100 days to mature, but there are a few hybrids that are marketed to mature in as few as 45 days. Early Girl is one of the hybrids that is supposed to mature in 45 days, but they have yet to prove themselves at my location in the southern Black Hills of South Dakota, which is over 5400 feet. When growing containerized tomatoes it is more important that the variety be suited to growing in containers than developed for faster maturity. Some of the varieties that work well in containers are Big Beef, Goliath, Celebrity, and cherry or patio tomato varieties.

Tomatoes require fertile soil that is high in organic matter. They are prone to soil borne diseases that generally develop because they are getting too much water or being watered too late in the day. When tomatoes are watered late in the afternoon or evening it doesn’t allow time for the leaves or soil surface to dry before darkness, which leads to fungal diseases. Fungal diseases generally develop in warm, dark, and moist conditions. Under-watering also will cause disease. Too little water at the critical time of fruit development can result in blossom end rot.

Components of the High Altitude Container Garden

Since tomatoes are fairly deep rooted plants, the size of the container is of utmost importance. The containers should be at least the size of a five gallon bucket or larger with large drainage holes. Self watering containers work well because their design doesn’t allow over-watering and the supply of water is constant. Self watering containers have a reservoir at the bottom of the container that holds the water with the plants and soil sitting on top of the water supply. There is a drain hole at the top of the reservoir so when it is full the water overflows. There are many designs of self watering containers on the market or they can also be designed and made at home. If the gardener chooses to use a standard container, even if it has sufficient amounts of large drainage holes, the container should be set on a couple of bricks to elevate it so the water can drain freely out of the bottom.

Soil fertility and structure are also very important for getting container tomatoes to mature and bear fruit. A mix of 2 parts good quality topsoil, 2 parts quality potting soil, and 1 part cured manure will meet the nutritional needs of containerized plants for the entire growing season. This mix provides better water retention and soil structure than if topsoil or potting media were used by themselves. The manure adds a rich, organic source of nutrients for the plants.

Once the large containers are filled with the soil mix and water is added, they will be very heavy and hard to move. This can be mitigated by putting the plantings on wheels. A standard moving dolly covered with a sheet of heavy plywood works well and can hold more than one container. Drill a hole in the plywood and attach a piece of rope or parachute cord to be used as a handle for moving it.

The Growing Process

At most high altitude locations the active gardening season can arrive as late as mid-June. However, a container garden can be planted in mid-to-late May if offered some protection at night and on cold days.

Plant the tomatoes in the large containers in the same manner as if they were to be planted outside. The bottom two-thirds of the branches should be clipped off and the plant set deep so that only the top third will be above the soil. This will allow development of a strong root system. Put a 2-inch layer of mulch over the soil, as this will not only help retain moisture, but also discourage soil-borne diseases by acting as a barrier between the soil and leaves. At some point during the planting process make sure to get the containers on wheels, before they get too heavy to lift.

Early in the growing season, the containerized plants can be wheeled into a garage or outbuilding at night and left inside on cold days to protect them from freezing. On the warm, sunny days they can be put outside in a location with full sun. If possible, it is beneficial to locate the containers on cement or gravel when they are outside, because those surfaces tend to absorb and hold the warmth longer than soil areas.

As the growing season progresses, the tomato containers can be left out night and day if there is no danger of frost, drenching rain or hail. The soil in the containers should be kept moist, but not wet. Ideally, it is best to water the plants in the morning, which gives the soil surface and leaves time to dry slightly during the day, thus reducing risk of disease. Drenching afternoon thunderstorms can result in soil that is too wet. In the event of storms, the containers should be moved to a covered location.

With any luck, the first of the tomatoes should be ripe in mid-to-late August, and continue to produce into October if protected from frost.