Tomato, Outdoor

Introduction

Tomato (Solanum lycopersicum) is a warm season crop of the Solanaceae, or nightshade family, along with pepper, eggplant, and potato, as well as tobacco, petunia, and several solanaceous weeds. Tomato is native to South America, with its use as a food crop originating in Mexico. Tomatoes grow best on well-drained soils that are high in organic matter. They are frost-sensitive and should be transplanted into fields once the soil has warmed. For earliest production, a light soil is preferred on a gently sloping (2% or less) site with a southern or eastern exposure. 

Types and Varieties

There are thousands of tomato cultivars available, and varieties might be selected based on market preferences for shape, color and flavor, as well as for ease of harvest and storage, and for tolerance or resistance to the many diseases that affect this crop. 

Indeterminate varieties produce stems that will continue to grow until killed by frost. They are well-suited to staking or trellising. Side shoots (suckers) should be pruned off weekly and the main stem secured to the stake.

Determinate varieties have stems that grow long enough to produce 2 to 3 flower clusters and then stop. It is necessary to allow the suckers to grow to produce more flowers. Determinate varieties are well-suited for ground, cage or basket weave culture.

It is generally agreed that varieties that are later to mature have higher quality than the earliest varieties.

Most varieties used by commercial growers are hybrids, generally labeled (F1), which are crosses produced by controlled pollination between 2 different varieties to select for the desirable characteristics of each. Seed produced by F1 hybrids are not genetically stable and tend not to breed true if saved. Plants produced from hybrid seed tend to be more productive and vigorous, and may be bred for resistance to specific diseases.

Heirloom varieties, which are open-pollinated and breed true from their own seed, are very popular in the marketplace. A great number of different varieties are grown and many have a following associated with individual markets. Try a number of varieties and continue to grow those your customers like. Most heirloom varieties carry no disease resistance. Verticillium and Fusarium can be particularly problematic. Use of cultural practices like field rotations and good sanitation is key.

Tomato Varieties - Outdoor
Early Cherry
Early Girl - IND, F12, V Matt's Wild - IND, EB, LB
New Girl - IND, F2, V Sungold - IND, F12, TMV, V
Polbig - DET, F1, TMV, V Sun Sugar - IND, F, TMV, C
  Sweet Million - IND, F12, TMV
Main Season Super Sweet 100 - IND, F1, TMV, V
Big Beef - IND, ASC, F12, N, TMV, St, V  
Defiant PHR - DET, ASC, EB, F2, LB, V  Heirloom
Florida 47 - DET, ASC, F12, St, V Brandywine - IND
Iron Lady - DET, EB, F12, LB, SLS, V Cherokee Purple - IND
Mountain Fresh Plus - DET, EB, F12, N, V Mortgage Lifter - IND
Mountain Magic - IND, EB, F123, LB, V Moskvich - IND
Mountain Merit - DET, F12, LB, N, TSWV Pruden's Purple - IND
Mountain Spring - DET, F12, St, V Striped German - IND
Sunguard - DET, ASC, F123, St, V  
Biltmore - DET, ASC, F12, TMV, V Grape
  Jolly - IND
Roma/Saladette Red Grape - IND, LB
Pony Express - DET, BS, F123, N, TMV, TSWV, V Tami G - IND
Plum Dandy - DET, EB, F1, V  
San Marzano - DET, F2, V  
Plum Regal - DET, EB, F12, LB, TSWV, V  
Sunoma - DET, BS, F12, N, St, TMV, V  

 

Resistant or tolerant to: ASC: Alternaria stem canker; BS: Bacterial Speck, C: cracking, EB: Early blight (Alternaria), F: Fusarium (races indicated where known), LB: Late blight Phytophthora), N: Nematodes, St: Stemphylium, TMV: Tobacco mosaic virus, TSWV: Tomato spotted wilt virus, V: Verticillium

Other codes: DET: determinate, IND: indeterminate

 

Soil Fertility

Apply lime according to soil test results to maintain soil pH at 6.5 to 6.8. Maintain high calcium. Base saturation for calcium should be 65%-80%. Use calcitic lime or gypsum if necessary.

When growing plants on plastic mulch, the amount of nitrogen fertilizer to be sidedressed can be reduced, and most of it can be applied when laying the plastic, since leaching is minimized. Nitrogen can be sidedressed along the edge of the plastic mulch. As an alternative, the use of trickle irrigation under plastic mulch permits fertigation. With fertigation, apply no more than 10 lb per week of actual nitrogen fertilizer per acre, preferably calcium nitrate (use a soluble greenhouse grade). A thirty-ton tomato yield removes about 200 pounds of nitrogen per acre while a fifteen-ton yield removes about 100 pounds of nitrogen per acre. On the "Plant Nutrient Recommendations" table, the nitrogen recommendation for outdoor tomatoes is figured on a yield goal of twenty-two tons per acre. Do not apply more nitrogen fertilizer than is required to achieve your realistic yield goal. Excess nitrogen can reduce yield. Use a liquid starter fertilizer at transplanting, especially with cool soil conditions. Use a high phosphorus starter fertilizer mixed at a rate recommended on the label. Apply 8 fluid ounces (1 cup) per transplant.

Less nitrogen fertilizer will be needed on some soils high in organic matter, or if manure or legume sod was plowed down (see Table 1, Nitrogen Credits from Manure and Table 2, Nitrogen Credits from Previous Crops).

When sidedressing nitrogen, the nitrate forms (such as calcium nitrate) are preferred over the ammonium or urea forms. This reduces the chances of blossom end rot occurring on the developing tomatoes. Tomatoes have a high requirement for potassium, but avoid excessive levels to reduce chances of blossom end rot.

PLANT NUTRIENT RECOMMENDATION ACCORDING TO SOIL TEST RESULTS FOR OUTDOOR TOMATO
OUTDOOR TOMATO NITROGEN (N)* LBS PER ACRE   PHOSPHORUS (P) LBS P2O5   PER ACRE     POTASSIUM (K) LBS K2O      PER ACRE
SOIL TEST RESULTS   VERY LOW LOW OPTIMUM ABOVE OPTIMUM VERY LOW LOW OPTIMUM ABOVE OPTIMUM
Broadcast and Incorporate 80-100 180 120 0-60 0 250 150 50-100 0-50
Sidedress 3-4 Weeks after Planting 30 0 0 0 0 0 0 0 0
Sidedress 6-8 Weeks after Planting 30 0 0 0 0 0 0 0 0
TOTAL RECOMMENDED 140-160 180 120 0-60 0 250 150 50-100 0-50
*SEE PLANT NUTRIENTS FOR INFORMATION ON NUTRIENT MANAGEMENT AND APPLICATION.

Planting

Tomatoes are transplanted in New England due to the short growing season. The key to early fruit production is growing good transplants with plenty of space during the transplant growing stage. Adequate spacing produces a short, stocky plant about as wide as it is tall with a good root system. Ideally, the plants should be spaced on the greenhouse bench so leaves do not touch or overlap during the transplant growing period. One ounce of tomato seed will produce about 7,400 plants.

Sow tomato seed in artificial mix (vermiculite-peat base works well) and maintain uniform moisture and bottom heat at 75°F until emergence. Some growers are using compost-based mixes. This is especially important for producing organically certified plants. Be sure the compost-based mixture is acceptable to the certifier. Transplant young seedlings into 2" to 3" plant growing containers when they have two true leaves. Alternatively, if there are facilities for producing plug transplants, you may want to experiment with this method for tomatoes.

For earliest production, some growers finish their transplants in 6" (or even larger) pots. For the later, main season crop, the smaller 2" to 3" containers are acceptable. Plants for a September-October crop can be started in 1" cells, but these containers are too small for earlier production. Do not attempt to hold plants in small cells. Plants will become leggy and production can be delayed 2 to 3 weeks.

Grow the transplants at 70°F to 75°F day and 60°F to 65°F night temperature. Night temperatures in the greenhouse below 60°F will likely result in rough fruit (catfacing) on the first few clusters. Five to 8 weeks from seed are required to produce field-ready transplants, depending on the temperature at which the plants are grown and the size desired. Do not start the plants too early; otherwise, they have to be over-hardened or held too long before planting. Harden only slightly, by reducing water and nutrients, and/or by transferring to a cold frame. Do not reduce temperature below 60°F. Small plants that have been slightly hardened, or not hardened at all, will outperform larger, over-hardened plants.

Transplants should be given a complete nutrient solution supplemented with trace elements (the latter especially if artificial mixes are used) at weekly intervals. Alternatively, they can be fed whenever they are watered with a dilute nutrient solution. The advantage to the latter system is that the fertilizer is supplied more in relation to the plant's needs: more on bright, warm days; less on cool, cloudy days. In either case, follow directions on the fertilizer label for amounts to feed. Use a soluble fertilizer and be careful of salt buildup. It is advisable to use a fertilizer in which most of the nitrogen is in the nitrate form rather than ammonium or urea.

Field Culture

Many growers are using black plastic mulch, which has several benefits. It warms the soil, promotes earliness, conserves water, permits use of less nitrogen fertilizer because leaching is reduced, and facilitates weed control. Plastic mulch also keeps most of the fruit off the soil. The disadvantages of plastic mulch are removing the plastic in the fall and disposing of it. Plastic should be laid tightly over the beds to conduct heat to the soil more efficiently and to avoid depressions where puddles can form. Many growers use plastic mulch in conjunction with raised beds. This warms the soil more quickly. Prior to laying plastic mulch, soil moisture should be at or near field capacity. Trickle irrigation (see Trickle or Drip Irrigation), with a fertilizer injector, can be profitably used with black plastic mulch. Providing a uniform moisture level should reduce or eliminate problems with blossom end rot and cracking. Hot caps or row covers are used by some growers for faster early season growth. They do not provide significant frost protection, but they do speed growth. Ventilation is usually needed on warm, sunny days. Do not allow temperatures under covers to exceed 90°F. (See Plastic Mulch and Row Covers, and High Tunnels.)

Trellising/Staking

Typically, properly pruned, staked or trellised tomatoes come into production 7 to 10 days before the same tomatoes grown on the ground. Early tomatoes usually bring higher prices, but perhaps not enough to justify the expense of tying and pruning them. Supporting and pruning the tomatoes also gets the plants and fruit off the ground, which reduces the incidence of Anthracnose ripe rot on fruit, and allows breezes to penetrate the plant canopy, reducing leaf wetness intervals and foliar disease spread. Pruning (removing the side shoots) should be done weekly. Shoots are most easily removed when they are a few inches long. To reduce disease, do not prune during wet weather or if bacterial canker is present. The plant is normally topped after the fifth cluster but can be topped later for late fall harvests. Leave several leaves above the uppermost cluster to provide shade and produce food for the developing fruit. Indeterminate plants are well suited to trellising or staking because the main stem keeps growing until it is topped. The plants can be pruned to 1 or 2 stems. For 2 stems, keep the lateral branch just below the first cluster. Two stems obviously yield more fruit/plant than a single stem, but pruning is much more difficult and time-consuming. Allow more growing space when pruning to 2 stems. The plants are either tied (3 to 4 times) to individual stakes or, in the trellis system, supported by weather-resistant twine tied to a number 9 or 11 wire, 5' to 6' above the ground. The lower end of the twine is tied loosely around the base of the stem. As the plants grow, the string is spiraled around the main stem. Pruning is usually done at the same time. Care is needed to prevent damage to the plant. The wire is held up by posts spaced 20' to 30' apart in the row. Metal fence posts help to support the wire, with sturdy wooden posts at the end. Most growers use the "A" trellis, a double row 18" to 24" apart. The "A" trellis uses fewer posts and less wire; fruit tends to be more shaded and sun scald is less of a problem. When twisting plants around the twine, care must be taken to avoid stem breakage.

Ground Culture and Basket Weave

The stems of determinate tomatoes stop growing after producing 1 to 3 flower clusters. For continued production, side shoots must be left on the plant. This results in a bushy, compact plant which is not suitable for staking or trellising.

Determinate varieties can be grown on the ground without support, but most growers are using a system called stake and weave or basket weave. With this system, wooden stakes 4' to 5' long and 1" square, or similar lengths of rebar, are driven 1' into the ground between every other plant. Weather-resistant twine is then tied to the end stake and run down one side of the row, wrapping the twine around each stake. Most growers weave the twine back and forth between plants. The process is then repeated on the other side of the row. The stringing operation is repeated 3 to 4 times with the first being 8" to 10" above the ground when the plants are 12" to 15" tall. Subsequent stringings are made just before the plants begin to fall over. There are many variations of this system. Note: birds cannot perch on the rebar, resulting in a cleaner crop at harvest. 

Twine should be resistant to weather and stretching.  Tomato twine for this purpose is available in 3 or 4-pound boxes. A home-made stringing tool should be used for convenience.  It is simply a length of metal or plastic conduit. The twine is fed through the conduit which acts as an extension of the worker's arm.

Most growers remove all the bottom side shoots up to, but not including, the one below the first flower cluster. After this, no pruning is done.

Spacing

Plant spacing will vary according to cultivar and type of culture. Frequent roadways may be necessary to drive spray or harvest equipment between blocks of rows.

Staked: Set plants 12" to 18" apart in rows when pruning to a single stem, 18" to 24" apart when pruning to 2 stems, and 5' between rows. 

Stake and Weave: 5' to 6' between rows, 18" to 24" between plants.

Ground: For small-vined (determinate) varieties, 4' to 6' between rows, set plants 12" to 24" apart within the row and for large-vined (indeterminate) varieties, set plants 2' to 3' apart in the row and 5' to 7' between rows.

High Tunnels

High tunnels (see High Tunnels and Tomato (Greenhouse) sections) allow for planting one to two weeks earlier than in the open field. Harvest is earlier and yields are usually greater. High tunnels keep rain off the foliage and fruit, resulting in fewer diseases and rain check (a russeting of the fruit). Sides are rolled up during warm weather, but should be lowered when temperatures fall below 60 degrees F.  

Irrigation

If there are no restrictions, tomatoes develop a deep root system. When irrigating tomatoes grown on black plastic, sufficient water must be applied so that lateral water movement can take place under the plastic to provide adequate moisture to the root system. Once fruit begin to enlarge, tomatoes require at least 1" of water per week depending on temperature, wind and relative humidity. (See also Trickle or Drip Irrigation.)

Harvest and Storage

Since most tomatoes are marketed in the New England area, it is recommended that tomatoes be harvested at the breaker to turning stage. Tomatoes harvested in the green stage do not promote the image of high quality as implied by the native tomato designation. Letting the fruit ripen completely on the vine improves the flavor somewhat. However, as tomatoes remain on the vine, they are subject to cracking and other disorders. Jointless varieties have no joint (looks like a knuckle) on the fruit stem. When picking, the stem separates completely from the fruit. With jointed varieties, the stem usually breaks at the joint, leaving a small stem attached to the fruit. This can puncture other fruit, and should be removed before placing in a container. Therefore, use of jointless varieties saves labor. Attempt to use jointless varieties, when available, to avoid damage to other fruit. Ripe tomatoes are easily damaged.

Tomatoes are susceptible to chilling injury if stored at temperatures below 50°F for more than 24 hours. Continual exposure to these temperatures will prevent normal ripening even after temperatures are elevated. Store tomatoes at 55°F or above depending upon how long the tomatoes must be stored. The speed of color development will increase up to 75°F. Temperatures above 80°F will inhibit red color development. For best eating quality, ripening and color development should take place between 65º to 70°F. Late in the season when night temperatures routinely drop below 50°F, tomatoes should be harvested in the breaker stage and ripened at room temperature.