Choosing Varieties and Root Media for Successful Greenhouse Tomato Production

Linda Benedict, Hanna, Hanna Y.  |  3/2/2010 1:32:12 AM

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Hanna Y. Hanna

Small greenhouse tomato operations are common in the United States. Rising transportation expenses, which now account for a substantial part of tomato production costs, provide new opportunities for marketing locally produced tomatoes at a reasonable price. Growers can produce a vine-ripened, attractive fruit to sell on the day of harvest at producer premises, farmer’s markets, road-side stands and local grocery stores. However, they have to reduce production costs and increase plant yield to gain market share among major producers.

The choice of an acceptable-yielding tomato variety with appropriate fruit qualities and longer shelf life is a vital grower decision. Failure to select an appropriate variety may lead to lower yield or less market acceptability. The tomato variety called Trust has been among the most recommended varieties in Mississippi and was popular in Louisiana, Texas and Alabama. The fruit shelf life of Trust, however, is short because of moisture loss through fine cracks on the fruit shoulder. Newer varieties, such as Geronimo and Quest, are being evaluated for yield, fruit quality and shelf life.

Growing media for tomato production include rockwool, perlite and shredded pine bark. Research at the LSU AgCenter Red River Research Station has indicated that perlite can be recycled to save money. Information on the initial cost of the media and their impact on tomato yield will help tomato growers reduce production costs and enhance plant yields.

The North American market demands large fruit. Fruit pruning – selectively removing individual fruit – is used to increase fruit weight and size by limiting the number of fruit per cluster and reducing competition among fruit. Previous recommendations for fruit pruning ranged from three to five fruit per cluster.

Two studies were conducted simultaneously and independently from 2006 to 2008 in two identical 30-by-96-foot greenhouses at the Red River Station to address these industry concerns. The objectives of the first study were to evaluate yield, fruit weight, fruit quality and shelf life of Geronimo, Quest and Trust varieties planted in perlite and pruned to three or four fruit per cluster. The objectives of the second study were to determine the initial cost of perlite, pine bark and rockwool as growing media and their effect on the yield of Quest variety pruned to three or four fruit per cluster.

In the first study, Geronimo, Quest and Trust, selected from among 10 previously evaluated greenhouse varieties, were planted in 5-gallon grow bags filled with perlite. Geronimo was selected because it produced high yields; Quest was selected for its shiny fruit; and Trust was selected because it has been popular among growers in Mississippi and Louisiana.

Five-week-old plants of all three varieties were transplanted in the grow bags. Two transplants were planted at a 3-inch depth and spaced 7 inches apart in each bag. Fruit clusters were pruned to remove excess fruit and flowers as soon as three or four fruit per cluster were visible in each treatment.

For fruit quality analysis, three to five ripe fruit having similar color and size were selected and liquefied in a food processor at early, mid and end-of-harvest season. Fruit nitrogen, potassium, sodium, pH and soluble solids (sugar) were determined. To test for shelf life, approximately 10 pounds of marketable fruit were harvested from each plot weekly, packed in tomato cartons and stored for one week in a cooled room at 67 degrees. After the storage period, firm fruit with no skin discoloration, shrinking or deterioration were considered marketable. The sum of marketable and unmarketable fruit for the entire season was determined and the percentage of marketable fruit was calculated for each trial.

In the second study, plants of Quest variety were grown for five weeks and transplanted into grow bags filled with perlite or pine bark. Plants for the rockwool treatment were grown in rockwool cubes for five weeks before being transplanted into rockwool slabs. Retail cost of growing media, transplant media and containers to grow 640 plants in one greenhouse was determined based on invoices received from suppliers.

Plants for both tests were grown from late November to early July in 2006, 2007 and 2008, according to LSU AgCenter recommendations. Fruit was harvested from early March to early July and graded according to U.S. Department of Agriculture standards. Early marketable yield was fruit graded medium or larger in the first five harvests. Total marketable yield was the marketable fruit graded medium or larger in all harvests. Cull yield was the unmarketable fruit.

Results of the first study indicate that Geronimo produced the highest early and total marketable yields; Quest produced intermediate yields; and Trust produced the lowest yield (Table 1). Geronimo and Quest produced lower cull yields and heavier fruit than Trust. Pruning clusters to three fruit significantly increased total marketable yield, reduced cull yield and increased fruit weight (Table 1). Trust produced fruit with higher nitrogen and pH (less acid) than the other two varieties. Quest fruit had higher potassium and sugar than Geronimo fruit. Fruits of all varieties had similar sodium content (Table 2). High nitrogen is not desirable as a quality component. But potassium is essential for fruit quality, and sodium is important for fruit taste. Approximately 92 percent of Quest tomatoes remained marketable after storage for one week at 67 degrees. Geronimo had 83 percent marketable fruit, and Trust had 78 percent marketable fruit (Table 2).

High nitrogen is not desirable as a quality component. But potassium is essential for fruit quality, and sodium is important for fruit taste. Approximately 92 percent of Quest tomatoes remained marketable after storage for one week at 67 degrees. Geronimo had 83 percent marketable fruit, and Trust had 78 percent marketable fruit (Table 2). Trust fruit had shorter shelf life because fine cracks on the shoulder led to moisture loss during storage. This defect was more common in Trust than in Geronimo and least common in Quest fruit.

The second study indicates Quest plants grown in perlite produced greater total marketable yield than plants grown in pine bark or rockwool. Perlitegrown plants produced significantly lower cull yield and heavier fruit than rockwoolgrown plants (Table 3). Results also indicated that tomatoes grown in pine bark or rockwool produced similar total marketable and cull yields but different fruit weights. As in the first study, cluster pruning to three fruits significantly increased total marketable yield, reduced cull yield and increased fruit weight (Table 3). It was more expensive to grow tomatoes in perlite and least expensive in pine bark (Table 4).

Quest produced higher total marketable yields than Trust in this study, and the fruit had significantly less nitrogen, higher acidity, longer shelf life and a shiny color that gives it a marketing edge over Trust. Geronimo produced higher yields than either Quest or Trust, but the fruit had less potassium and sugar than Quest and lacked the shiny color and the shelf life of Quest. Geronimo and Quest should be considered as replacements for Trust by growers in the Southern states. Geronimo should be considered for its higher yield and Quest for its adequate yield and shiny fruit that has superior shelf life. It is recommended growers grow these varieties on a small scale first because possible environmental effects may affect their results.

Tomato breeders release few greenhouse varieties each year, and knowledge about their performance is extracted from the description released by the company. Many smaller growers, particularly new ones, depend on communication with established growers to choose a variety. For example, Trust has been more popular than any other variety in Southern states because of grower interaction during workshops. This study indicates that Geronimo and Quest can be appropriate alternatives to Trust and can help growers produce more yield per unit area and extend fruit shelf life. Geronimo’s higher yield can compensate for its less-thanoptimum shelf life.

Perlite can be recycled for many years to reduce production cost without negative impact on yield. Rockwool can be steam-sterilized and reused once and then must be disposed of because of fiber breakdown during steam sterilization and handling. A significant cost is associated with the disposal of rockwool. Pine bark properly composted to grower’s specifications is hard to find and is difficult to recycle because it turns to slush as it continues to decompose during the growing season.

This study indicates that tomatoes grown in perlite produce higher yields, which can make up for some of the initial cost of the medium. Perlite can be recycled successfully for many years to reduce production expense in following years. Properly recycled perlite can save money, time and natural resources.

In the past, tomato growers were not persuaded to prune clusters to an exact number of fruit because of conflicting reports about the optimum number of fruit that can lead to higher yields and heavy fruit. These two studies indicate that fruit was heavier and plants produced more marketable yield and less cull yield if only three fruit were left on each cluster.

Smaller-scale growers in Louisiana and other states are encouraged to consider these recommendations:
– Plant Geronimo or Quest.
– Prune clusters to three fruit.
– Use perlite as a growing medium and recycle it properly.
– Heat plants at the root level.

These recommendations may help the local producer survive serious competition from imported greenhouse tomatoes.

Hanna Y. Hanna, Professor, Red River Research Station, Bossier City, La.

(This article was published in the winter 2010 issue of Louisiana Agriculture.)


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