Tomatoes 201: A production guide

Photos courtesy of Christopher J. Currey

Hydroponic tomatoes are the most popular fruiting vine crop for control-environment agriculture. They are popular with consumers, especially during the winter, but they are also an economically important crop for growers, too. A previous two-part Hydroponic Production Primer — “Tomatoes 101” — shared the fundamentals of growing hydroponic tomatoes in greenhouses. This article is going to offer a few tips on how to produce more flavorful and unique tomatoes. (Editor’s note: You can find “Tomatoes 101, part 1” at bit.ly/tomatoes-101-part-1 and “Tomatoes 101, part 2” at bit.ly/tomatoes-101-part-2)

An opportunity exists to diversify into more exotic and intriguing tomatoes with the use of heirloom tomato cultivars. Some heirloom tomato cultivars are already fairly popular, such as ‘Brandywine’ or ‘Cherokee Purple’, but there are many more. Heirloom tomatoes were selected for their flavor and unique appearances, as they can deviate wildly from the red beefsteak types commonly grown in greenhouses. If they’re so great, why aren’t more growers doing it? It is not impossible to grow hydroponic heirloom tomatoes, because some are already doing it, but it’s not without its challenges. Chief among those challenges is the cracking that may occur on fruits as are growing. Unlike the tomato cultivars that have been bred specifically for hydroponic production in greenhouses, heirloom tomato plants have been selected over the years in a field environment. The rapid rate of fruit growth that occurs with optimal growing environment and ample provision of nutrient solution in hydroponic system causes fruits to crack. By conducting your own trials to determine which heirloom tomatoes can be grown successfully in your system, you can have flavorful and unique fruits to offer your customers.

Growing a flavorful tomato is the goal for every producer. There are clear differences in flavor among cultivars. Some cultivars simply have a higher sugar content or Brix than other cultivars. Similarly, the acidity can also vary with cultivar. In addition to differences in genetics, the production environment and culture also influence flavor. For instance, increasing light intensity can help boost Brix due to enhanced photosynthesis compared to fruits developed under low light. Brix can also be enhanced by managing the nutrient solution, both the nutrient concentration (as measured by electrical conductivity; EC) and frequency of irrigation. First, moderate increases in the EC during the day can impart a slight salt or osmotic stress. This osmotic stress can reduce the amount of water taken up by tomato plants. With less water uptake, fruits do not expand as much and, as a result, the total soluble sugars, or Brix, is enhanced. Do not take the elevated EC approach too far, as it could result in salt damage to the roots. Reducing irrigation frequency can also achieve a similar boost in Brix to fruits. By diminishing the amount of nutrient solution provided to plants, the same inhibition of excessive fruit growth occurs as with the osmotic stress from elevated EC, as well as the same boost in Brix. Since the principle behind both of these practices suppresses fruit growth to some extent, there may be a slight yield penalty, with respect to fresh weight. However, this should cause you to discount these strategies right away. Increasing fruit quality and producing premium tomatoes may allow you to command a higher price for your product, which could offset any reduced yield from plants.

The popularity of hydroponic tomatoes grown in greenhouses cannot be doubted. And while the market expands, as will the number of producers to meet this increasing demand, consider differentiating your product through better flavor — whether it is the unique appearance and appealing flavor of heirlooms, or high Brix red beefsteaks.

Christopher (ccurrey@iastate.edu) is an associate professor of horticulture in the Department of Horticulture at Iowa State University.