Production of Greenhouse Tomatoes
Producing Tomatoes inside a greenhouse or anti-aphids structure can be quiet rewarding
The tomato is a very popular crop for production in greenhouses. Tomatoes are relatively easy to grow compared to cucumbers and lettuce, and yields can be very high. Demand for tomatoes is usually strong because of the vine-ripe nature and general overall high level of eating quality.
Production of tomato is not without serious challenges, however. This chapter presents the production techniques specific to tomato. Techniques used with certain systems (bag, rockwool, or NFT) will be highlighted separately. The production information is presented as recommended procedures. Minor adjustments might be needed as individual growers require and as research indicates the need. Growers are encouraged to consult a knowledgeable expert prior to making adjustments.
Selection of Cultivars
Selection of the most suitable cultivar (variety) is a prerequisite for successful tomato culture in Florida. Tomato producers should have in mind the type of tomato desired by the buyer (direct to consumer, broker, retailer, etc.). Important considerations are size, shape, and color (red, pink, yellow, or many others in the heirloom category). Important characteristics relative to culture include flavor, high yields, freedom from cracking, disease resistance, high percentage of number one fruits, and freedom from green shoulder. More recently, however, specific production practices or systems have been used to grow determinate types to be grown for a shorter season, perhaps spring or fall only.
Generally, greenhouse tomato cultivars are indeterminate in growth habit (produce flowers and fruit continuously along the main stem as it grows). As a result, the greenhouse tomato plant may reach a length of 30 to 40 feet in a 10-month season.
Modern tomato cultivars are hybrids that are more disease resistant than older open-pollinated types. Hybrid cultivars have replaced open-pollinated cultivars in all large tomato producing areas in the United States. For tomato cultivars to perform well in Florida in a traditional August–June season, they must be able to set fruit well in the winter, have freedom from russet or other cracking disorders, and be free of greenshoulder (solar yellows). New cultivars are continually released by seed companies so growers are encouraged to contact a knowledgeable specialist to determine the availability of newest cultivars. Tomatoes grown in Florida greenhouses from 1980 to 2000 were generally separated into two categories, beefsteak or cluster (on the vine). Since about 2000, the diversity of tomato types grown in Florida greenhouses or other similar protected agriculture structures has increased. In addition to beefsteak and cluster types, a wide array of heirloom, grape, and small cocktail types are now grown. Since many heirloom and other types do not have resistance to common greenhouse diseases, such as Fusarium wilt, grafting onto disease-resistant rootstock has become a more common practice.
Cultivars in the beefsteak category produce large (6 to 8 ounce) fruit. The fruits are harvested individually and usually packed with the calyx still attached. Beefsteak cultivars have been used for nearly all of the Florida greenhouse tomato production until the late 1990s when a few growers began to produce cluster types.
These products are known as cluster tomatoes, cluster-harvested tomatoes, truss tomatoes, or on-the-vine tomatoes. The term “truss tomatoes” is frequently used in Europe, and “cluster tomatoes” in the United States. Cluster tomatoes are currently grown as a greenhouse crop throughout the world. The product has gained preference among consumers because the calyx and stem remain attached to the cluster of fruit and the aroma from the stems gives the product a distinct fresh characteristic. This new way of marketing tomatoes is credited to Italian producers who first began testing in 1989. The popularity of this vine-ripened product quickly swept through the European greenhouse tomato industry, and more recently the North American industry. The large greenhouse tomato industry in Holland began its shift toward cluster tomatoes in 1992. Greenhouse culture of cluster tomatoes is similar to that used for traditional large beefsteak types. Most currently grown cultivars tend to have taller plants requiring very high trellis systems.
The clusters are harvested by clipping the main cluster stem from the plant. All tomatoes on the cluster remain attached and range in maturity from breaker to ripe. Harvested clusters are usually marketed in a mesh bag, tray pack, or in a single-layer box.
Many cluster tomato cultivars have outstanding flavor and appearance to compete with the best of the field vine-ripe tomatoes sold. Consumers also enjoy harvesting the fruit from the cluster themselves. Outstanding fruit quality and shelflife allow the consumer to pick tomatoes from the cluster over several days. The postharvest quality of the calyx is therefore an important characteristic in the appearance of the cluster.
Most greenhouse tomato crops are grown today with very little pesticide sprays applied to the crop. This is especially true in northern states in the United States and also in Canada. Environmental controls are important in managing diseases, and biological pest control has become a standard practice. Insect and disease management in Florida greenhouses is much more challenging because of the climate conditions and high pest populations. This is given special note because the presentation of the cluster of tomatoes means everything to the rise in popularity of cluster tomatoes. The clusters are generally free of any visible pesticide residue. If routine applications of pesticides are to be required in any production system, inside or outside of a greenhouse, the residue could be a significant detraction. At the least, it would face great competition from the current production free of visible residues. Washing of clusters of tomatoes to remove the residue from the stems and fruit would be very difficult.
The increase in demand for year-round, direct-to-consumer sales has driven the increase in acreage of other specialty types of tomatoes, such as heirloom, grape, and cocktail (small fruited types harvested on the vine). In most cases, the yields of these types are less than the more standard beefsteak or cluster types. However, much higher prices at local markets have caused an increase in production of these types in Florida, not only in standard greenhouses, but also in high tunnels, open shade structures, and even outdoor hydroponic systems with no protected structure. The heirloom category in particular is susceptible to root and crown diseases that have required many commercial operators to implement the use of grafted plants where the preferred cultivar plant top is grafted onto a disease-resistant rootstock. The wide array of tomatoes grown also provides a challenge in plant management in terms of trellising, leaning and lowering, and suckering. Cultivars with tall, open plant habits are much more susceptible to sun burning fruit and may need to be pruned and suckered differently to best manage the plants. As production is moved to outdoor culture, fall/winter seasons only, or in open structures, an additional consideration is to select cultivars with resistance to yellow leaf curl virus, which is transmitted by the silverleaf whitefly. The virus is usually less of a problem in greenhouse production because the whitefly populations can be reduced by excluding their entry into the production area.
The selection of a tomato cultivar for hydroponic production in a greenhouse or other protected culture has become a much more complex decision since early in this century. Making the correct cultivar choices and implementing the appropriate production and trellis systems are critical to success. New cultivars appear every year. Check with knowledgeable professionals or other growers to learn what you need to make the right choices.
Pruning and Training
Greenhouse tomatoes, as a result of their indeterminate growth habit, require continuous pruning and training to the trellis system. The trellis system consists of wire cable stretched from one end of the house to the other between two anchor posts. The anchors should be metal posts cemented into the greenhouse floor. A counter support, deadman will help strengthen the end posts. The cable is stretched tightly over each row of plants at a height of 8 to 10 feet and fastened on one end to a cable tightener. The downward pull exerted on the cable by a single tomato plant with five or six well-developed clusters of fruit might be 10 to 12 pounds. Therefore, extra supporting posts will be needed every 20 to 30 feet down the row of plants. Cable diameter should be at least 1/16 inch with 3/32 inch preferred.
Plants are trained up a string attached to the cable above the plant and extending to the base of the plant. Trellis strings are made up ahead of planting, keeping in mind that a 10-month-old tomato plant might be 30 feet long. Different growers have individual preferences on the technique to use to attach the string to the trellis cable and the resulting facility for quickly releasing the plant to lower it. One system is to roll the extra “future” twine in a ribbon or ball and hang it over the cable with enough extra twine to enable the ribbon to dangle. The downward string is then clamped to the upward string by a plant clip. Another option is to attach the string to the wire via a slip knot that can easily be released. There are also commercially available metal string bobbins on which to wrap the twine and which also function as a hanger, or a notched spool with a hook.
String used for trellising should be strong plastic or polypropylene twine. Polypropylene hay baling twine and tomato staking twine work well and are about the least expensive products available. In addition, they can be secured locally.
To start the procedure of trellising the plant, the lower end of the twine is loosely fastened to the base of the plant. This operation usually starts when the plant has 6 to 8 large leaves and before the plants start to topple.
There are basically three methods to attach plants to the twine. The first method involves using plastic plant clips (1 inch size) available at most greenhouse supply outlets. The twine is clamped in the hinge of the clip, and the clip is snapped around the plant stem just below a large leaf. It is not a good idea to clip at the flower cluster node since the flower cluster stem might be crimped and damaged. Clipping is done every 3 or 4 leaves to keep the plant tops attached to the twine.
The second system involves the use of a plastic ribbon tape in place of most of the plastic clips. The ribbon can be applied by a hand fastener machine (tapener) that wraps the tape around the twine and plant stem and staples the ribbon (Fig. 18). This method is much faster than the clipping method. However some clips still must be used since, in the tape method, the plant stem is free to slide down the twine. A clip fastened just below a leaf is used every three or four tapes to keep the stem anchored to the twine.
The third system involves simply wrapping the plant stem around the twine as it climbs the twine. This system avoids the expense of clips and tape, but is more likely to result in damage to the plant stem. This damage results from the pressure to force the stem to wrap the twine and from the abrasion of the string on the stem.
Forth (and this is our own addition as this article was written way back before HORTOMALLAS was available or widely known in the US greenhouse business) is the use of HORTOMALLAS tomato net where the tomatoe vine can be interwoven in between the meshes at a 30 degree angle or fastened with the use of clips or ties, or even better the plant should be sandwiched in between two walls of trellis netting as a way to reduce contact with the workers hands during the training phase, as contact with the worker´s hands can spread diseases mechanically.
Greenhouse tomatoes require pruning of all lateral branches (suckers) as they develop to encourage a single leader. Pruning helps in the overall management of the long-term tomato crop. Pruning must be done on a frequent schedule (every 3 to 4 days) so that only small side shoots are removed. Excessive intervals result in large shoots that are difficult to remove, resulting in serious damage to the plant and increasing the likelihood of disease.
Pruning is best done early in the day when plants are turgid but dry. Suckers snap out of the leaf axils easily, resulting in a clean wound that heals easily. Growers need to be careful to remove only suckers and not the main terminal bud. Sometimes, this is difficult to do when several suckers are present in the top of the plant. During sucker pruning, any leafiness in the flower cluster should be pinched out. Pruning early in the day allows the wound to dry sufficiently during the day making it less susceptible to decay organisms. It is best not to prune during cloudy periods because drying of the wounds is not optimal.
The pruning time should be used to inspect plants for obvious problems, such as disease, nutritional problems, insects, etc. All pruned plant material should be placed in a container or bag and removed from the greenhouse.
Cluster Thinning Tomatoes produce anywhere from one to about 10 flowers per flower cluster. Under good pollination conditions, about six to eight of these flowers might form fruits. For many cultivars, especially large-fruited cultivars, this is too many fruits to develop properly. If too many fruits are allowed to set on a cluster, fruit size, shape, quality, and uniformity are sacrificed. Shape is sacrificed because excessive numbers of fruits in a cluster cause compression damage to neighboring fruits as they develop. Quality is reduced because of the poor shape and because the small, later-setting fruits are prone to blotchy-ripening. Nonuniformity results because maturity occurs over a long period and may overlap fruits on higher clusters.
To alleviate these fruit problems, tomato clusters should be thinned to provide an optimum number of fruits per cluster . If the cultivar has the capability to produce high yields of large fruits, and this is the goal of the grower, then clusters should be thinned to three to four fruits. Cultivars with intermediate fruit size can be thinned to four or five fruits. Rarely will leaving more than five fruits in a cluster pay off with the large or medium-size fruiting cultivars. Clusters should be thinned to the lower number of fruits in winter period.
Those cultivars being grown for “cluster” tomatoes where the entire cluster is harvested at once may need some thinning to remove off shape of extra, very small fruits. Small fruited “cluster” tomatoes may not need thinning.
Cluster pruning should be done about once per week. This allows several fruits in a cluster to set so that a choice can be made regarding which to remove and which to leave. The objective should be to thin the cluster to a group of fruits that are most uniform in size and age. Cracked fruits and misshapen fruits should be removed no matter the size.
When cluster thinning, workers must be sure to take care not to rub or scratch fruits to be left. Small abrasions early in fruit development result in large scars at harvest. It is a good idea to check clusters a week or two later to remove any small fruits that developed since the previous thinning. If automatic vibrating pollination systems are used, cluster thinning will play a large role in achieving good fruit quality.
Credit: G. J. Hochmuth, The Florida Greenhouse Vegetable Production Handbook http://edis.ifas.ufledu/cv266
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