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By Lynn Byczynski
Without tomatoes, there might not be a local food movement. Local tomatoes — ripe, fragrant, and flavorful — brought many people to farmers markets and roadside stands because supermarket tomatoes had strayed too far from the real essence of America’s favorite summer vegetable. Those hard, pink, and tasteless tomatoes became the emblem of a food system gone awry.
And though an appreciation for locally grown has expanded to include all produce, tomatoes remain one of the most important crops for most small, direct-market farms. Farmers understand the importance of great-tasting tomatoes, both financially and symbolically, and they are constantly seeking to improve tomato flavor.
In this article, we’ll look at three of the latest trends in tomato growing: dry farming, amending soil with salt, and not rotating tomatoes.
Dry-farmed tomatoes have been grown in California for more than a decade and the practice is spreading nationwide. In places where it never gets too hot, growers water tomatoes for the first week or two after transplanting, then never water again. In hotter areas, growers might water only until the plants flower, and then either cut off water entirely or provide much less than normal.
The flavor of dry-farmed tomatoes, advocates claim, is extraordinarily good. And they bring a premium price.
“There’s almost a cult following for these tomatoes,” said Aziz Baameur, University of California Extension Advisor for Small Farms and Specialty Crops, based in Santa Clara County.
When he first talked to growers who were practicing dry farming, he said, “it sounded like a mystique thing; it was never really explained in a sense that was factual. But the flavor was great.”
So Baameur decided to do some research on dry farming tomatoes to see if the flavor was really better and to learn just how much water stress tomatoes could handle without yielding significantly less. He set up five irrigation treatments, based on an evapo-transpiration model called the California Irrigation Management Information System (CIMIS); the program is a network of weather stations that report how much water plants lost through evapotranspiration (ET) the previous day. The system is designed to help growers know how much to irrigate to replace the amount of water lost, while preventing overwatering. In Baameur’s plots, he grew tomatoes at 0, 25, 50, 75 and 100 percent of ET.
In a report, not yet published, he wrote: “Tomato variety ‘Early Girl’ was used since it has proven adaptable to water deficient treatments. Eight week-old plants were transplanted to the field and watered for a week before drip irrigation regimes were imposed. The 100% ET treatment received all the water needed to satisfy its ET needs, while the other treatments received decreasing increments of water.”
Taste panels preferred the fruit grown in the 0, 25, and 50 percent plots, and laboratory analysis confirmed that the stressed tomatoes were higher in sugars, soluble solids, and lycopene. Ripe fruit color was good in all treatments, and skin toughness was reported only in well-watered fruits.
As for yield, total yields did not vary significantly among the five treatments, although the marketable yields were lower in the most water stressed plots. The three driest treatments had fewer large and extra-large fruits, more rejects due to insect and disease damage, and more blossom end rot and sunburn.
Baameur noted that the first trial was in a coastal area, where the temperature rarely goes over 85°F and fog prevents a high rate of evapotranspiration. A second trial in a hotter location was modified so that the plants were irrigated until they flowered, and then the five irrigation treatments were implemented. The results were similar — dry-farmed tomatoes had the best flavor and yield was somewhat, though not dramatically, lower.
True dry farming works only in places that don’t get a lot of summer rain, or in high tunnels, where watering is controlled. But in many other places, water stress is often used to improve tomato flavor.
“I am a big fan of dry farming, and I know it can work in the East, though of course it is not as reliable as in California or somewhere dry,” said Andrew Mefferd, a product technician at Johnny’s Selected Seeds Research Farm in Maine. “For example, in 2006 my wife and I were growing mixed vegetables for sale at my grandmother’s farm in Pennsylvania. We put drip irrigation on our tomatoes but only irrigated them when we started to see the first signs of wilt. It was a fairly normal year for precipitation (average amount, evenly distributed), and if memory serves we only turned the water on to the tomatoes once or twice. I thought the tomatoes tasted very good that year and we got a lot of positive feedback from our customers at market.”
Mefferd said that growing tomatoes on the dry side did reduce yields, but added, “the way I think about it, farmers market customers don’t come back to me because I can get X tons per acre; they come back because I’ve got the best-tasting tomatoes, so I personally would take a yield reduction for a flavor augmentation.”
Growers in the South are advised to reduce water for better flavor in the publication Sustainable Practices for Vegetable Production in the South: “For maximum yield, adequate water levels need to be maintained throughout fruit development. For maximal flavor, however, a slight water stress during fruit development (60 to 80 percent of the estimated requirement) is sometimes recommended. Probably the most important consideration in watering tomatoes is consistency. When water availability fluctuates or when it is too high or too low at critical stages, fruit disorders develop.”
In Oregon, Shari Sirkin stops watering tomatoes in June to intensify their flavor. She says yield is reduced, so she just grows more plants. In Colorado, Ewell Culbertson uses water stress to get his final tomatoes of the season to ripen before frost. He stops irrigating in July so the plants will focus their energy on producing fruits rather than on vegetative growth.
But growing tomatoes under water stress isn’t for everyone. “I agree that growing drier can produce better flavor,” said Dave Chapman of Long Wind Farm, an organic greenhouse tomato grower in Vermont. “However, stopping the irrigation for a long season indeterminate crop is not a very good strategy. In order to continue setting fruit and growing, the plants require some water. In a greenhouse crop, the level of production is very high. It is very intensive agriculture. If I underwater, the first thing that suffers is the fruit set.
“Too much water is bad, as it leaches out the nutrients. If it is really bad, it can drown the roots, and even create denitrification in the soil.Too little water can be a problem, as it affects fruit set, fruit size, and can create a soil with too much sodium due to pulling the salts in the soil to the surface through evaporation. The high level of sodium can help improve flavor, but it creates a hostile environment for root growth. Too little water can also create blossom end rot. So can too much water.”
Salt and flavor
Israeli researchers studying whether brackish water could be used to irrigate tomatoes stumbled upon an unexpected result: tomatoes grown with salty water tasted better. Chemical analysis showed that percentage of dry weight, total soluble solids, sugars, and acidity — all factors that contribute to good tomato flavor — were higher in saline-treated plants than control plants. Italian researchers also found better flavor from tomatoes grown with salt. At Rutgers University in New Jersey, Dr. Joseph Heckman realized that a lack of sodium could be responsible for less flavorful tomatoes.
“In the ‘olden days’ Chilean nitrate (sodium nitrate) was widely used as a nitrogen source in vegetable crop production,” he writes. “But in recent decades it has mostly been replaced with other nitrogen fertilizers that do not provide sodium.”
To test the salt-flavor connection, Heckman drove to the Jersey shore and collected a barrel of water from the ocean. He took it back to the Rutgers Vegetable Research Farm and used it to treat a group of tomatoes.
“The sea water treatment consisted of a one-time, over the top drench (1.5 liters of sea water applied per plant) of the plants during early bloom. A control group was drenched with regular tap water. Although the sea water caused some burn to foliage, the plants soon recovered. Once the tomatoes were vine ripe, the students working in my lab preformed a blind taste. The results, in terms of taste preference, were clearly in favor of the fruit produced by the sea water treated plants. Sea water, of course, contains sea salt.”
To follow up, for the past several years he has grown tomatoes in soil amended with SEA-90 (available from www.SeaAgri.com), a material derived from marine deposit that is a rich source of sodium, chloride, and many other naturally occurring minerals. The first year, trials were conducted at two different research farms, with different cultural practices. Taste tests of the tomatoes showed a preference for the salt-treated tomatoes from one farm, but for the untreated tomatoes from the second farm. The trials were conducted again last year and again were inconclusive, this time with one variety performing better than a second variety. Research will continue this year, Heckman said.
To growers who want to experiment on their own tomatoes, he has these suggestions: “Apply 23 grams of SEA-90, a commercial product that contains mostly sea salt. It is enough material to treat 4 square feet of area or the soil needed to grow one tomato plant. Apply the treatment by mixing the SEA-90 product into the soil at time of planting or early flowering. Flag the treated plant and perform your own personal taste test by comparing the treated fruits to other fruits of the same tomato variety from another part of the field. Leave some border space between plants when sampling fruits for comparing treated and untreated plants.
“A free alternative to use of the commercial product is sea water from the Atlantic Ocean. 650 ml (or 0.172 gallons) of sea water contains about 23 grams of salt which is enough to treat one tomato plant.”
Heckman has not used table salt and could not comment on it. However, sea salt is available from the health food section of the grocery store and, according to the label, 23 grams is about 4 teaspoons.
Soil tests of the New Jersey tomato trials showed a slight elevation of salts in the soil, but Heckman said he did not see any adverse effects on growth or yield of tomatoes, nor would he expect to from such a slight increase. However, he cautioned that high tunnel tomatoes might be harmed because salts already tend to accumulate in the soil inside a high tunnel.
An incidental discovery in all the salt research has been that salt treatments cause tomatoes to ripen faster. The Israeli researchers concluded that salinity shorted the time of fruit development by 4 to 15 percent. The New Jersey researchers also were struck by how much earlier the salt-treated tomatoes ripened.
For more information on the salt experiments:
The most frequently heard advice about rotating crops is that you should never grow Solanaceae family crops (tomatoes, potatoes, peppers, eggplants) in the same place two years in a row because of the threat of soilborne diseases overwintering in soil and affecting future crops. In fact, most authorities recommend four years between solanaceous crops.
But greenhouse and hoophouse growers frequently grow tomatoes in the same spot every year. And some old-time growers believe that tomatoes taste better when grown in the same soil. Eliot Coleman mentioned that folklore in his book The New Organic Grower. “They even recommend fertilizing them with compost made from the decayed remains of their predecessors,” he writes. “I once grew tomatoes that way for eight years in a greenhouse. In truth, they were excellent, and they got better every year. I do not grow field tomatoes that way now and cannot really defend my decision except to say that it is more convenient when they are part of the rotation...I suggest that you try growing tomatoes (or any crop, for that matter) without rotation. Nothing is as stifling to success in agriculture as inflexible adherence to someone else’s rules.”
Dave Chapman of Long Wind Farm grows tomatoes in the same spot every year, but removes and replaces 6 inches of soil from the beds before each new crop. “I have no idea whether tomatoes get better when grown in the same place year after year,” he said. “It is my experience that every year is so unique, with so many factors changing, that it is difficult to know which cause created which effect. I know of a farm that has grown tomatoes in the same soil in a greenhouse without removing any soil for over seven years, and they have seen no reduction in yield or quality, so it certainly isn’t a given that you need to rotate in order to maintain a good crop. It should be pointed out that they have come in with a heavy topdressing of compost every year.”
Chapman, like many greenhouse and hoophouse tomato growers, uses grafted plants. This increasingly popular technique involves grafting a fruiting variety onto a disease-resistant rootstock variety. Growing for Market covered this topic In May 2008. You can read the article here:www.growingformarket.com/articles/20080526_1
Johnny’s Selected Seeds has a video on tomato grafting.
Lewis Jett, a West Virginia Extension specialist in commercial horticulture, conducted extensive research on hoophouse tomato production at his previous job at the University of Missouri. He was asked whether rotating is really essential. He answered:
“The decision to rotate is more complicated in the high tunnel since usable space has such a high opportunity cost. Growers seem to be pulled towards monoculture of high-value early season crops like tomatoes. I must admit, my recommendation to conventional high tunnel vegetable producers has been that they can grow successive crops of tomatoes in the high tunnel as long as they are not observing any foliar or soil disease problems. They should amend the soil between cropping cycles with organic matter. So, disease management has been the index for whether to rotate or not. A lot of people may differ with this.
“I believe there is a point where soil quality declines from growing heavy feeders like tomatoes. From my experiences in Missouri, it seemed to be six to seven consecutive crops of tomatoes.”
In summary, these three practices are thought to improve tomato flavor. Although the research at this point is somewhat inconclusive, it does provide food for thought, and basis for experimentation, in the quest for the most delicious tomato.
Lynn Byczynski is the editor and publisher of Growing for Market, the trade magazine for market gardeners and farmers. GFM is published 10 times per year, and every issue is full of practical, hands-on articles that can help you be a better grower and marketer. If you are a commercial grower selling food and flowers in local markets, you should be reading GFM! Here's how to subscribe.