Tomato, Outdoor

Introduction

Tomato (Solanum lycopersicum) is a warm season crop of the nightshade family (Solanaceae), along with pepper, eggplant, and potato. Tobacco, petunia, nicotiana, and several important weed species are also solanaceous. Tomato is native to South America, with its use as a food crop originating in Mexico. It grows best on well-drained soils that are high in organic matter. It is frost-sensitive and should be transplanted into fields once the soil has warmed. 

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 perform best when staked or trellised. Side shoots and suckers arising from the base of the plants should be pruned off weekly and the main stem should be secured to the stake. Indeterminate cherry, grape and some plum/”saladette” vines are often more vigorous than indeterminate slicing tomato vines.

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 and fruit per plant. Determinate varieties are well-suited for ground, cage or basket weave culture.

Several tomato varieties can be classified as “vigorous determinates,” and are important commercial production varieties. They produce a higher percentage of grade A fruits when they are staked. Under good conditions, they can produce 15 to 20 lbs. per plant, but require more space.

Varieties that are later maturing are of higher market quality than the earlier varieties, but early varieties are important for early-season customer attraction. Cherry tomatoes are appealing throughout the production year, as are “cocktail” and “saladette” types. Interest in the less juicy paste/Roma-type fruits is usually during late summer to early fall.

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/Open-Pollinated varieties are very popular in the marketplace. A diverse array of varieties are available and many growers create their own market identities by reliably producing them. Most heirloom varieties carry little or no disease resistance. Verticillium, Fusarium, Alternaria and Septoria can be particularly problematic. Cultural practices like field rotations and good sanitation are essential.

Recently, a number of “hybrid heirlooms” have been introduced. These have appearance and flavor similar to heirlooms, but also have more resistance to leaf spot and vascular pathogens and are not as subject to as much variability in fruit size and shape. 

Tomato Varieties
Fruit Type Variety Season/Size Growth Habit Disease Resistances*
Hybrid Slicing Be Orange Main/Large Indeterminate V, F1, F2, FCRRR, LM, TomMV
  BHN 589 Main/Large Vigorous Determinate V, F2, TMV
  Big Beef Main/Large Indeterminate V, F1, F2, St, TMV, N
  Early Girl Early/Medium Indeterminate V, F1, F2
  Geronimo Main/Large Indeterminate V, F1, F2, TMV, LM, PM
  Manitoba Early/Small-Medium Compact Determinate V, F
  Mountain Fresh Plus Main/Large Vigorous Determinate V, F1, F2, N, EB, GW, BER
  Mountain Merit Early/Large Compact Determinate V, F1, F2, N, TSWV, EB, LB
  New Girl Early/Small-Medium Indeterminate V, F1, F2
  Primo Red Early/Large Compact Determinate V, F1, F2, TMV
  Red Deuce Main/Large Vigorous Determinate V, F1, F2, TMV, St
Heirloom/OP Amish Paste Variable Plum Indeterminate None
  Black Krim Early/Medium Indeterminate LB
  Brandywine Main/Large Indeterminate EB, FB
  Cherokee Purple Main/Large Indeterminate BS, F1, F2, F3, N, TSWV
  Green Zebra Early/Small Vigorous Indeterminate LB, SLS
  Principe Borghese Small oval cherry Vigorous Indeterminate None
  Pruden's Purple Main/Large Indeterminate None
  San Marzano II Elongated plum Indeterminate F, N, TomMV
  Striped German Main/Large Indeterminate Unknown
  Yellow Pear Early pear-shaped cherry Vigorous Indeterminate None
"Hybrid Heirloom" Caiman Main/Large Indeterminate F1, N, LM, TomMV, TMV, TSWV, V
  Damsel Main/Large Indeterminate LB, N, V
  Marbonne Main/Large Indeterminate F1, TomMV
  Margold Main/Large Indeterminate LM, TomMV, V
  Marnero Main/Large Indeterminate F1, EB, FCRRR, TomMV, V
Hybrid Paste/Plum Golden Rave Early/Small-Medium Vigorous Indeterminate F, F1, TomMV, TMV
  Granadero Main/Medium Indeterminate V, F1, F2, TMV, PM, N, TSWV
  Juliet Early/Small Vigorous Indeterminate EB, LB, SLS
  Plum Regal Main/Medium Vigorous Determinate EB, F1, F2, LB, TSWV, V
  Verona Early/Medium Indeterminate V, F1, F2
Hybrid Cherry Black Cherry Large Vigorous Indeterminate None
  Favorita Medium Vigorous Indeterminate F2, N, LM, TMV
  Sakura Large Vigorous Indeterminate F1, F2, N, LM, TMV
  Sun Peach Medium Vigorous Indeterminate LM, TMV
  Sungold Small-Medium Vigorous Indeterminate F1, F2, TMV, V
  Sunsugar Medium Vigorous Indeterminate F1, V

*Resistance Key: EB=Early Blight; LB=Late Blight; SLS=Septoria Leaf Spot; F1, F2, F3=Fusarium race1,2,3; TomMV=Tomato Mosaic Virus;; TMV=Tobacco Mosaic Virus; TSWV=Tomato Spotted Wilt Virus; LM=Leaf Mold; PM=Powdery Mildew; V=Verticilium; FCRRR=Fusarium Crown Rot and Root Rot; N=Root Knot Nematode
 

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. Leaf tissue testing can be an important tool to monitor the nutrient status of your plants. If testing is done at the right time (early to mid bloom), additional nutrients, most importantly N and K, can be supplemented. While these can be side-dressed along the edge of the plastic mulch, nutrients can be applied more effectively in soluble form through drip irrigation installed under the plastic. Liquid suspensions of organic nutrients can be applied this way as well, but drip lines should be flushed regularly. If this method is used, apply no more than 10 lbs. per week of actual nitrogen fertilizer per acre.

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 high P liquid starter fertilizer at transplanting, especially with cool soil conditions. 

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 side-dressing nitrogen, the nitrate forms (such as calcium nitrate) are preferred over the ammonium or urea forms. While maintaining adequate calcium in the soil is essential, blossom end rot is a physiological disorder in which the plants allocate more calcium to vegetative growing tips than to developing fruit. It usually occurs during the early ripening period, and much more commonly on Roma-type tomatoes. Adequate irrigation is essential during this time.

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 quality transplants. Adequate spacing produces short, stocky plants with good root systems, whereas crowding produce tall, spindly plants. One ounce of tomato seed will produce about 7,400 plants.

Sow tomato seed in an open flat in germination mix and maintain uniform moisture and bottom heat at 75°F until emergence. Transplant young seedlings into 2" to 4" cells or pots when they have two or three true leaves. Choice of pot size depends on weeks before anticipated field transplant date.  For earliest production, some growers finish their transplants in 6" (or even larger) pots. 

Grow transplants at 70°F to 75°F day and 60°F to 65°F night temperatures. Night temperatures in the greenhouse below 60°F may result in irregular 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. Avoid the temptation to start the plants too early; holding them for too long will reduce yield. Harden only slightly, by reducing water and nutrients, and ambient temperature, if possible but not 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 use black plastic mulch, which has several benefits. It warms the soil, promotes early production, 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 Irrigation), with a fertilizer injector, is a very efficient watering method used under black plastic mulch. Consistent soil moisture reduces or eliminate problems with blossom end rot and cracking. Row covers over wire hoops 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

Staking or trellising certain varieties may advance production by 7 to 10 days. Early tomatoes usually bring higher prices, but  this has to be weighed against trellising labor. Fruit quality and plant health may be enhanced by keeping fruit off of the ground and allowing air movement into the plant canopy, reducing the incidence of Anthracnose ripe rot on fruit, and foliar disease spread. Pruning (removing the side shoots) should be done frequently for fully indeterminate varieties. 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. Indeterminate plants are well suited to trellising or staking because the main stem keeps growing. 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 per plant than a single stem, but pruning is more  time-consuming and each plant requires more space.  For trellising, plants are supported by weather-resistant twine tied to a number 9 or 11 wire, 5' to 6' above the ground.  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. 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. For staking, plants are tied (3 to 4 times) to individual stakes. Avoid damage to plants during trellising and staking operations.

Ground Culture and Basket Weave

The stems of fully 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; vigorous determinate varieties are usually supported 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 (vigorous determinate and indeterminate) varieties, set plants 2' to 3' apart in the row and 5' to 7' between rows. Remember that there will be significant losses due to fruit rots if indeterminates are left unstaked.

High Tunnels

High tunnels (see High Tunnels and Tomato (Greenhouse) sections) allow for planting up to four 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 foliar 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. Watering should be deep and spread out across the bed. This can be accomplished by running at least two drip tapes per bed. 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. These varieties work well for bulk packaging because stemless fruit do not puncture other fruits in the box. With jointed varieties, the stem usually breaks at the joint, leaving a small stem attached to the fruit. This makes for an attractive retail item but requires special handling and more boxes, since fruits cannot be layered on top of each other.

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 they 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.