In 2003, U.S. greenhouse growers produced ≈175,996 tons of tomatoes; however, imports still exceeded domestic production, with 282,323 tons from Canada and Mexico alone (Cook and Calvin, 2005). This factor provides opportunities for growers to increase U.S. greenhouse tomato production. As of 2003, large (>40 acres) and medium (7–40 acres) operations accounted for 62% and 15%, respectively, of total U.S. greenhouse tomato productivity (Cook and Calvin, 2005). Over time, the largest U.S. greenhouse firms have shifted locations to align production with the most profitable market windows and use the warmer winter climates while simultaneously targeting the high-priced winter season (Cook and Calvin, 2005). Although this shift allows profitable production all year-long, it also increased transportation expenses. This, according to Hanna (2009), accounts for a substantial part of tomato production expenses and usually mandates growers to cut costs, increase yield, or both.
Small greenhouse tomato operations are still prevalent in the United States and focus mainly on local sales on the premises or to farmer's markets and retailers (Cook and Calvin, 2005; Korevaar, 2007). In order for these small family farms to compete in the market, they must either tap into a niche market, such as heirlooms or cherry tomatoes, or reduce production costs and increase plant yield (Korevaar, 2007; Hanna, 2009). In short, despite the size of operation or location, growers are always pursuing ways to increase yield.
Greenhouse tomato production requires many environmental, cultural, and biological practices to optimize production and fruit quality. Plant density and pruning methods are two important cultural approaches to increase yield. It has been recommended by Snyder (2007) and the Louisiana State University AgCenter (2009) that each tomato plant should receive 4–4.3-ft2 growing area, with about a 13.7–15.7-inch spacing between plants and 4 ft between rows. Previous tomato studies, grown in both field and greenhouse conditions, have demonstrated various responses to plant density. With greenhouse-grown cherry tomato, Charlo et al. (2007) found that increasing plant spacing from 11.8 to 19.7 inches resulted in greater yield per plant but lowered productivity per unit area, while decreasing plant density resulted in greater yield per area but smaller more nonmarketable fruit. Similarly, Saglam and Yazgan (1995) reported that tomatoes grown in unheated greenhouses had overall yield per unit area increase with an increased density. Kemble et al. (1994) found no yield differences between in-row spacing of 12 and 30 inches in field-grown tomato. However, Santos et al. (2010) determined that higher yields of field-grown tomatoes were obtained by using smaller in-row spacing.
Franco et al. (2009) stated that choosing a proper pruning system was important to keep a balance in the relationship's source/sink and the carbon/nitrogen (C/N) ratio. There are several reports that confirm the benefits of pruning on tomato yields. Cockshull et al. (2001) found a tendency for side shoots to reduce the yield of marketable fruit produced on each cluster in greenhouse production.
Pruning needs differ depending on the growth habit of the cultivar, but typically it is recommended that indeterminate greenhouse tomato plants be pruned to one stem by removing all side shoots (Snyder, 2007). However, literature indicates that productivity per unit area increases when pruning tomato plants to two stems. Aung (1999) reported that greater marketable yield per unit area was obtained by pruning indeterminate field tomatoes to two stems rather than one stem. Borisoy et al. (1978) found that greenhouse tomato yield per unit area increased 10% to 15% when pruned to two stems rather than one. Common pruning studies compare one plant with one leader and one plant with two leaders. This study was designed to compare two production systems, one using one plant per grow bag pruned to a double leader, the other using two plants per grow bag each pruned to single leaders. Growers are exploring ways to decrease production costs by cutting back on the number of transplants needed by using one plant with two leaders per 5-gal grow bag instead of two plants with one leader per grow bag. However, there is not adequate data to support the yield benefits and possible cost savings to support this practice. The objective of this study was to evaluate different plant densities and pruning production systems to maximize yield and fruit size for indeterminate tomatoes grown hydroponically under greenhouse conditions.
Aung, M. 1999 Effect of pruning and spacing on performance of fresh market tomato AVRDC 1-7. AVRDC—The World Vegetable Center Bangkok, Thailand
Borisoy, V.Y., Borisova, R.L. & Belik, V.T. 1978 The dependence of tomato yield on spacing and plant training Puti Povysheniya Urozhainosti Plodov i Ovoshchnykh Kul'tur 54 59
Charlo, H.C.O., Castoldi, R., Ito, L.A., Fernandes, C. & Braz, L.T. 2007 Productivity of cherry tomatoes under protected cultivation carried out with different types of pruning and spacing Acta Hort. 761 323 326
Cockshull, K.E., Ho, L.C. & Fenlon, J.S. 2001 The effect of the time of taking shoots on the regulation of fruit size in glasshouse-grown tomato crops J. Hort. Sci. Biotechnol. 76 474 483
Cook, R. & Calvin, L. 2005 Greenhouse Tomatoes Change the Dynamics of the North American Fresh Tomato Industry 4 Mar. 2011. <http://postharvest.ucdavis.edu/datastorefiles/234-447.pdf>.
Franco, J.L., Rodriguez, N., Diaz, M. & Camacho, F. 2009 Influence of different pruning methods in cherry tomato grown hydroponically in a cropping spring cycle: Effects on the production and quality Acta Hort. 843 165 169
Hanna, H.Y. 2009 Influence of cultivar, growing media, and cluster pruning on greenhouse tomato yield and fruit quality HortTechnology 19 395 399
Kemble, J.M., Davis, J.M., Gardner, R.G. & Sanders, D.C. 1994 Spacing, root cell volume, and age affect production and economics of compact-growth-habit tomato HortScience 29 1460 1464
Louisiana State University AgCenter 2009 Greenhouse Tomato Production Handbook 11 June 2011. <http://www.lsuagcenter.com/NR/rdonlyres/38D013C6-A7BF-4702-88DC-921E038778F8/10111/HannaTomatoBook.pdf>.
Rodriguez, B. & Lambeth, V. 1975 Artificial lighting and spacing as photosynthetic and yield factors in winter greenhouse tomato culture J. Amer. Soc. Hort. Sci. 100 694 697
Saglam, N. & Yazgan, A. 1995 The effect of planting density and the number of trusses per plant on earliness, yield and quantity of tomato grown under unheated high plastic tunnel Acta Hort. 412 258 267
Santos, B.M., Scott, J. & Ramirez-Sanchez, M. 2010 In-row distances and nitrogen fertilization programs for ‘Tasti-Lee’ specialty tomato HortTechnology 20 579 584
Snyder, R.G. 2007 Greenhouse Tomato Handbook. Mississippi State Ext. Ser. Bul. P1828 18 Oct. 2011. <http://msucares.com/pubs/publications/p1828.htm>.
U.S. Department of Agriculture 2007 United States Standards for Grades of Greenhouse Tomatoes 4 Mar. 2011. <http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5050332>.