Greenhouse Tomato Culture
There are several methods used to produce greenhouse tomatoes. However, the basic cultural requirements of the plant are similar. The following describes some of the factors to be considered.
Temperature plays a key role in the production of quality fruit. In general, optimum right time temperatures should be maintained between 60 degrees - 65 degrees F. This provides for good fruit ripening with no reduction in growth or fruit set. Optimum daytime temperatures should be maintained between 70 degrees to 80 degrees F, but do not artificially heat the greenhouse above the desired night temperature during daylight hours. Employ maximum cooling when temperatures within the greenhouse exceed 80 degrees F.
Air movement is also important in tomato production. Air in the greenhouse should be circulated when the exhaust fans are not operating. Circulation maintains a constant level of humidity and helps reduce potential problems from plant diseases.
Row and Plant Spacing
Work aisles between pairs of tomato rows are normally 36 inches. The rows in the pairs should be no closer than 28 to 30 inches. This allows light to penetrate to the lower leaves of plants in the close rows.
Plant spacing in the row should be 3.1 to 3.4 square feet per plant and narrower rows may sometimes result in greater yields, the value of the increased yield often does not offset the cost of the increased labor required to care for the additional number of plants.
1. Single crop rotation-seeded in July or by early August. Transplants set in greenhouse within 10 to 30 days of seeding. Harvest begins from 85 to 100 days following date of seeding and continues into June or early July. Cessation of pollination is six weeks before termination of the crop. Growing point is allowed to grow for at least five to seven leaves above last fruit truss to help prevent sunburned fruit. Remove flower buds above last fruit truss to assure no additional fruit set.
2. Two crop rotation-Fall crop seeded and transplanted same as for a single crop. Normally fall crop terminated from late December to mid-January with cessation of pollination from 55 to 60 days earlier. Spring crop seeded 30 to 35 days before transplanting into the greenhouse which is the day following termination of the fall crop. Harvest begins in late March to early April and usually continues through June.
Pruning and Training
Greenhouse tomatoes are trained to a single stem by removing all side shoots as they develop in the axils of the leaves. These side shoots or ýsuckersţ should be removed weekly by breaking them off or rubbing them out when quite small.
Transplants are set in most media so that the stem is covered about one-half inch above the line of the previous media. Before the plants grow more than about a foot in height when they generally start falling over, support the plant by tying plastic twine (1,000 to 1,200 feet per pound), with one end secured to the stem near the base of the plant [with a loose fitting non-slip loop] and the other end attached to a No. 9 to 10 gauge wire supported 7 to 8 feet above the row. As the plant grows, the twine is wrapped around the plant with one complete spiral between consecutive fruit trusses. Always wrap the twine in the same direction, clockwise or counter clockwise.
When the plants grow to the overhead wire, they are lowered about 2 to 2 ½ feet. When the plants again grow to wire, they are lowered with the same procedure repeated until the time when fruit setting is stopped. The lowering or dropping of the plant is accomplished by loosening the twine at the wire. If the original twine length did not allow a three foot pigtail after tying, a new five foot piece of twine is tied to the end of the other twine, and then the plant is lowered. The twine is again attached to the wire about 2 to 2 ½ feet down the wire from when it was originally tied so that about 2 to 2 ½ feet of stem rests on the ground. At the end of the cropping season, for one long, single crop, the top of a plant in a row may be more than 10 feet down the wire from where it originally started. The leaves on that part of the stem laying on the ground should be removed to prevent the creation of a disease hazard.
When lowering the plants, one row of a pair is dropped in one direction and the other in the opposite direction. At the end of the row, the plants are dropped across to its paired row rather than allowing them to ýbunch up.
Vibrating the flower clusters is the means of transferring the pollen from the anthers to the stigma of the blooms and is necessary for fruit set. The wind is normally responsible for this transfer in the garden and field.
In the greenhouse, pollination is accomplished by electric vibrators (battery or 110 volt), electric toothbrushes, mist blowers, striking the overhead wires with a broom handle while walking down the rows or automatic systems which shake the overhead wires either longitudinally or across the wires.
The electric vibrators manufactured for the purpose are normally more effective than the lower vibrating frequency of the electric toothbrushes. Both are time consuming.
To be highly effective, the air stream of the mist blowers must be directed at the individual flower clusters. The broom handle technique as well as the automatic vibrators are not too effective until the plants are about 2 feet or more in height when the weight of the plants keep the twine taut.
Experiments in a Midwest greenhouse showed that vibrating the flower clusters with a 110-volt vibrator every day versus every other day between the hours of 10 a.m. and 2 p.m. resulted in no difference in number or size of fruit. However, pollinating before 10 a.m. or after 2 p.m. reduced the number and size of fruit. An advantage of an automatic pollinator other than labor saving is that it could be adjusted to operate every day for a few seconds as various times between 10 a.m. and 2 p.m.
Normally tomatoes must be harvested 3 times a week except during the winter when yields are usually low and twice weekly is sufficient. When possible, the fruit should be harvested as they approach full-red color. The nearer tomatoes approach full ripens on the vines, the heavier and more flavorful they become. When left on the vine to ripen, an average of 20 percent increase in weight of the fruit which occurs between the time that the first trace of color is apparent on the fruit and the time the fruit is fully colored.
Some Problems and CausesBlossom-end-rot - Calcium deficiency as a result of too little calcium, too much potassium and magnesium and possibly ammonium nitrogen in relation to calcium or lack of aeration in growth medium.
Square and puffy fruit - carbohydrate deficiency as a result of too little sunshine or shade on greenhouse covering.
Blossom drop - same as puffy fruit above or also can result from a manganese deficiency. Sometimes, plants set about 30 fruit each before fruit truss begin to ripen. This is about maximum load for a plant with a result that blossoms drop until stress is relieved by harvest.
Thin stems near growing point - low nitrogen, too little moisture in growing media, low total nutrients, or excessive total salts or nutrients.
Bun at edges of lower leaves, thin stems at top of plant, and dark green shoulders on fruit - excessive total salts or nutrients. Leach growing media and water to remove salts.
Deformed leaves and leaflets at growing point occurring during the heating season, leaflets more serrated than normal, leaflets blotchy, leaflets appear somewhat like they had been sprayed with 2.4-D herbicide, and if above systems severe, than bloom buds fail to develop but turn yellow and may drop - combustion products from heaters usually ethylene. Check heat exchangers for cracks, and allow sufficient outside air to enter greenhouse so that combustion products can be exhausted out the vents.
Failure of flower buds to develop into blooms - deficiency of manganese especially during December and January. Also can be manganese toxicity in which case new leaves usually show interveinal chlorosis somewhat like magnesium deficiency rather than iron deficiency chlorosis.
Interveinal chlorosis in newer leaves at time of plant - iron, manganese or zinc deficiency. With zinc deficiency, the leaves will be much shorter than normal. With manganese deficiency, the bloom buds will also fail to develop into blooms.
New leaves twist and curl downward into a ball-like growth, stems and internodes between leaves very short - nitrogen too high with low boron. Increasing boron to roots may not help but boron sprays at top of plant helpful. Decrease nitrogen or restrict water which in effect decreases nitrogen availability.