Bonnie Cox, Oregon Tilth
Tomatoes are adapted to a wide range of growing conditions, but low temperatures and short growing seasons can limit growth. Tomatoes perform well on medium textured sandy loams or loams but can be grown successfully on many soil types, from light sand to heavier clay loams, as long as the site is well drained. Sufficient moisture must be maintained to establish the plant and carry it through to fruit production. Tomatoes prefer slightly acidic soils with a pH of 6.0 to 6.8. Growing tomatoes on sandy soils, which warm earlier in the spring, encourages early fruit production. In selecting a site, the need for good air flow must be balanced with the risk of strong wind setting plants back. A site with good air drainage will reduce foliar disease problems and help prevent early spring and late fall frosts. However, young plants should be protected from cold spring winds, so a semi-sheltered field site with a windbreak offers protection that speeds maturity.
Soils should be prepared early by incorporating organic matter and cover crops well before the planting season. If a cover crop is in place, it should be turned in at least 3 weeks before transplanting. For more on this see the section (VI) on primary tillage in the tillage basics article. In areas where wind protection is needed, a cover crop (especially rye, wheat, oats, or hairy vetch) can be strip-tilled to provide standing cover crop strips to buffer wind around recent transplants. For more information on organic soil and nutrient management see the eOrganic articles Conventional Chemical Soil Testing within Organic Systems and Organic Soil Fertility.
Cover crops play a vital role at Perrywinkle Farm. They improve soil quality, provide nutrients, prevent erosion, moderate soil temperatures, conserve moisture, and help control insect, weed, and disease problems. This tomato crop benefits from a thick layer of mulch grown in place as a rye cover crop from fall to early spring. They do not import straw mulch from off-farm for fear of weed seeds. Photo credit: Debbie Roos, North Carolina Cooperative Extension.
Several different cultural systems are used in the commercial production of tomatoes. The field design selected will be guided by soil conditions, training system, variety, and need for tractor access. Variables to consider include seeding method (direct or transplants), the use of shaped beds, and plant spacing.
Direct Seeding or Transplants
Most commercial field-grown tomatoes are produced from transplants, however processing tomatoes or mechanically harvested fresh-market tomatoes are often direct seeded. For more see production of transplants for organic tomatoes and the article on potting mix basics. Establishing a healthy tomato stand by direct seeding can be difficult and requires a greater amount of seed per acre, which increases seed cost. Soil crusting caused by rainfall occurring after seeding can be a problem in silty soils. Disadvantages of direct seeding tomatoes include increased weed pressure, extra investment in preparing a suitable seedbed, risk of washing out or deeply burying seeds during irrigation or rain, and delayed planting date compared with transplants.
Fresh market tomatoes are commonly produced on shaped raised beds with plastic mulch. Raised beds warm earlier in the spring which can enhance early production. Beds also facilitate good drainage and can improve production on poorly drained soils. However, under dry conditions, raised beds may require increased irrigation. If raised beds are used in combination with plastic mulch, drip irrigation is usually installed beneath the plastic to improve water delivery to the plants and maintain the integrity of the plastic mulch. Beds are typically 3–8 inches high and 30–36 inches wide.
There are many different arrangements for plant spacing that can all provide the necessary space for growth. For a discussion of training systems, see the related article Training Systems and Pruning in Organic Tomato Production. A priority for fresh market tomatoes is fruit size which is enhanced by adequate spacing. Processing tomato producers aim to maximize yield and often plant at higher densities to produce a higher total yield, but of smaller size tomatoes. The optimal plant population per acre will also be influenced by features of the cultivar: plant growth habit, size at maturity, and vigor. Overcrowding plants can result in poor fruit set and delayed maturity.
Field grown fresh market tomatoes can be planted at densities of 3,200–5,700 plants per acre if unstaked or, 2,400–3,200 plants per acre if staked. Processing tomatoes which are grown unstaked can be planted at densities of 4,000–4,800 plants per acre. One rule of thumb is to space plants so that determinate varieties have 9 square feet (18 inches X 6 feet) and indeterminate varieties have 15 square feet (30 inches X 6 feet). Within-row spacing will also depend on the vigor of the cultivar and how heavily it will be pruned.
|End Use||Vine Habit||Between Row Spacing||In-Row Spacing|
|Fresh-Market||Small-vined, staked||4, 5, or 6 feet||12-18 inches|
|Small-vined, unstaked||5 or 6 feet||12-18 inches|
|Large-vined||5 or 6 feet||18-24 inches|
|Processing||Determinate, unstaked||5 or 6 feet||
6-9 inches (single plant)
9-12 inches (seeded in clumps)
Tomato roots can reach a depth of up to 6 ft. if growth is unobstructed; however, the majority of root development occurs in the upper 24 inches of the soil. Tomatoes also have a high water requirement. A mature tomato crop can use more than 1 gallon of water per plant per day when solar radiation is high. The most important consideration in tomato watering is consistency; water stress contributes to physiological fruit disorders such as blossom end rot and cracking. For maximum yields, adequate water levels need to be maintained throughout fruit development. It is also important to avoid waterlogging tomatoes, as they are sensitive to extreme fluctuations in moisture.
Farming practices that increase soil organic matter content and improve soil structure will enhance soil water holding capacity and minimize the magnitude of soil moisture fluxes--important factors in producing high quality and marketable tomatoes. Soil moisture is increased directly by the high water holding capacity of organic matter. In addition, organic matter acts indirectly to improve in soil structure and porosity. Mulches improve water relations in two ways, by conserving water, and by reducing fluctuations that stress the plant and cause cracking and blossom end rot. Common organic farming practices such as cover cropping, compost applications, reduced tillage, and the use of organic mulches all improve soil structure and reduce fluctuations in plant available water.
Water requirements will vary with climate, soil type, and plant size. On average, tomatoes will use 1–1.2 inches of water weekly. Irrigation systems used in tomato production include surface and furrow flooding, overhead sprinklers, and drip or trickle. Flood irrigation requires the least equipment but is also the least water use efficient. Flooding is mostly used for large scale plantings. Sprinkler irrigation is sometimes used, but wetting the fruits and leaves and splashing of water from soil to foliage will increase the risk of disease. Drip irrigation efficiently supplies needed moisture directly and at a more consistent rate to the crop plants compared to overhead irrigation systems but materials costs and labor are higher. Drip systems also reduce weed growth if drip lines are placed close to plants. Even in areas with rainfall during the tomato production season, access to irrigation is necessary in order to prevent extreme variations in moisture that can lead to fruit damage, particularly during fruit development.
Problems Associated with Poor Water Management
Moisture stress can cause a number of physiological problems in tomatoes. Moisture stress during flowering can cause blossoms to abort without setting fruit. Fluctuations in moisture or moisture stress during fruit development affects calcium uptake by roots, resulting in a high incidence of blossom end rot. Extreme fluctuations in moisture during fruit growth also increase problems with cracking as the inner layers of the fruit expand more rapidly than the surface causing the skin to open in radial or concentric cracks. Watering too heavily or heavy rain after a long dry spell results in cracking. Prolonged foliar wetting periods and splashing of water from the soil to the foliage and fruit encourage diseases such as early and late blight and anthracnose.
Enhancing Flavor with Water Management
Some growers choose to water stress plants slightly during fruit development in order to enhance fruit flavor. Providing 60–80% of the normal water requirement during fruiting can intensify flavor. Managing water in this way is a useful tool for specialty markets, such as tomatoes grown for sun drying. Tomatoes grown for processing often receive reduced water in the later stages of fruit development in order to increase the soluble solids content.
Field grown tomatoes are generally pollinated through wind vibration, and secondarily through bumblebee activity, so farmers typically do not consider tomato pollination in field crops an issue as it is in greenhouse tomato production.
The days to maturity will vary with cultivar and growing conditions. Most tomato varieties will produce mature fruit 70–125 days after planting. As a guideline, tomatoes usually ripen 6–8 weeks from fruit set but this varies by region. The following stages of ripeness are commonly recognized for tomatoes:
When to harvest will depend on how the fruit will be handled and used. Fresh market fruit for local consumers can be picked red, while fruit that will be transported long distances should be harvested at the mature green or breaker stage.
Organic growers marketing directly to consumers frequently harvest vine ripe fruit. It is generally agreed that the edible quality of a tomato is best if it is harvested at the light red to red stage. Vine ripened fruit looks and tastes best, but it is more delicate to transport.
Conventionally grown tomatoes sold in wholesale markets are often picked at the mature green stage and ripened in storage with the use of ethylene gas. However, in organic production systems ethylene gas is not permitted for tomato ripening—it can only be used for postharvest ripening of tropical fruit and degreening of citrus. Tomatoes naturally produce ethylene and mature green tomatoes will ripen on their own at 70°F in 14 days, or at 55°F in 28 days. Tomatoes can be ripened in well ventilated open cardboard boxes that are checked frequently so as to quickly remove rotting tomatoes. For storage of mature green tomatoes, temperatures should range between 55°F and 70°F.
Harvesting for the fresh market is almost always done by hand, although in large fields mechanical harvest aids may be used to transport workers down the row or to convey fruit to bulk bins. Riper fruit picked at the pink stage should be handled with care and field packed to avoid damage. If the fruit is harvested with the calyx on, care must be taken not to puncture neighboring tomatoes with the sharp stem end.
In the field, pickers should clean the plants of any decayed fruit and carry it off the field to avoid contamination of neighboring healthy fruit and of the field soil. Fruit should not be harvested wet as surface moisture increases the accumulation of heat and encourages disease development. These sanitation principles are particularly important in organic agriculture as the organic producer has fewer control options available once a disease presents itself. Prevention, including good sanitation practices, is an important component of organic disease management.
Good field management during harvesting is critical in order to pack a high quality product. Tomatoes at the breaker stage or riper are susceptible to bruising during handling. Harvest crews must carefully place tomatoes in picking bins and avoid dropping fruit. A drop of more than 6 inches onto a hard surface can cause internal bruising that is not visible until the fruit is cut open. Bruised tomatoes suffer from a water-soaked breakdown of internal cell tissue. Physically damaged tomatoes are susceptible to invading disease organisms that cause decay in the fruit tissue.
Bruising and other types of damage can be avoided through careful handling during and after harvest. Picking buckets must be unloaded gently to avoid bumping fruit. Bins should not be overloaded because the weight of tomatoes can compress and damage lower layers of fruit. Harvested fruit should be shaded to avoid heat-up before the fruit is handled at the packinghouse. Tomatoes held in the hot sun for just one hour can be as much as 25 degrees F warmer than fruit held in the shade (Hurst, 2006), and excessively warm fruit is more susceptible to breakdown.
At the end of each harvest day, all picking buckets should be cleaned and sanitized to prevent the spread of any disease organisms to the next day’s harvest. Rinse buckets with water to remove soil and field debris, then wash them in a sanitizing solution. See the related article Approved Chemicals for Use in Organic Post Harvest Systems for more on this topic and guidelines for use.
The quality of a tomato after harvest will only be as good as its quality during its development in the field. Postharvest quality is not determined only by postharvest handling; a number of preharvest factors have great effect on final fruit quality. See the related article Influence of Preharvest Factors on Postharvest Quality for more information.
When tomatoes are taken out of the field they may be washed and dried before sorting and packing. Handling the fruit with care during all of these steps is critical to reduce losses.
If fruit is mechanically damaged, it is more susceptible to invasion by organisms that cause decay. Bruises are the most common type of damage to tomatoes, but cuts, punctures, scars and scuffs are also inflicted through poor handling. Punctures are especially common from the stem of one tomato breaking the surface of another tomato. Scuffs and scars occur when tomatoes rub against rough surfaces of bins, cartons, or dirty sorting belts. Tomatoes packed tightly can even scuff each other through repeated rubbing, especially if they are dirty. Scuffed and scarred tomatoes develop pitting and browning as the injured tissue dries out.
If a mechanized system is used in the packinghouse each step should be analyzed to reduce dropping, throwing, and squeezing of the fruit. If a drop is necessary, padding with 1-inch thick foam rubber substantially reduces injury. Avoid drops of 6 inches or more. Dumping fruit into water instead of onto a solid surface can also help reduce bruising.
Washing and Drying Tomatoes
Washing tomatoes with a sanitizing solution removes dust and other debris and reduces the incidence of postharvest rots such as Anthracnose, but care must be taken to manage the wash water to prevent contamination from waterborne pathogens.
Tomatoes can be washed with a spray of water or by submerging in a water tank. In washing, care should be taken to heat the water to a temperature several degrees F above the temperature of the fruit pulp. This prevents the internal contamination of the fruit by waterborne pathogens--the use of colder water would cause the fruit’s air spaces to constrict, creating a vacuum that draws in the wash water through the stem scar. Protected within the internal seed cavity, pathogens would be safe from the action of surface sanitizers. Pathogens can also enter tomatoes if they are submerged too deeply or for too long in wash water. Avoid submerging tomatoes deeper than 12 inches or for longer than 1 minute.
Wash water is usually mixed with an organically approved sanitizer (chlorine, ozone, peroxyacetic acid, etc.) to reduce the potential for harboring pathogens that could infect the fruit. See the related article Approved Chemicals for Use in Organic Post Harvest Systems for more information. If using a washing tank, maintain the water free of dirt and debris to increase the effectiveness of the sanitizer.
Tomatoes can be dried with a soft cloth, by air, or for larger operations with an air blast dryer. Ensure that washed tomatoes are completely dry before packing to prevent disease during storage and shipping.
Sorting, Packing , and Postharvest Diseases in Tomatoes
Tomatoes are commonly sorted or graded by size and quality. Tomatoes that are damaged, decaying, or cracked should be set aside or discarded.
Tomatoes can develop many postharvest diseases including Alternaria rot (Alternaria alternata), gray mold or Botrytis (Botrytis cinerea), rhizopus or hairy rot (Rhizopus stolonifer), and sour rot (Geotrichum candidum). Bacterial soft rot caused by Erwinia spp. can be a serious problem if good harvest and packinghouse sanitation practices are not implemented. Wounds and stems and stem scars provide potential points of entry for pathogens and decay organisms, so wounded fruit should be discarded immediately. (Boyette et al. n.d.)
To read case studies about organic tomato production, see the following links:
This is an eOrganic article and was reviewed for compliance with National Organic Program regulations by members of the eOrganic community. Always check with your organic certification agency before adopting new practices or using new materials. For more information, refer to eOrganic's articles on organic certification.