Growing Tomatoes in Hydroponics

Tomatoes are one of the most popular plants to grow in hydroponics; both for hobbyists and for commercial farmers

Commercial growers most commonly use greenhouses.
 
Home growers may use a small home greenhouse; or even grow a few tomatoes on a verandah, in a courtyard or in front of a window in a well lit part of the house. 
 
Growing conditions
  • Requires 21 to 24 degrees C for optimum growth.
  • Growth slows significantly below 18 or above 27 degrees C.
  • Requires good aeration and drainage.
  • In very hot conditions some shading is needed.
  • Avoid very high humidity.
 
 
 
Nutrient requirements
 
Essential elements for proper growth and development in tomato production include oxygen, hydrogen, nitrogen, carbon, phosphorus, calcium, sulphur, magnesium, manganese, iron, copper, zinc, boron, and molybdenum. Any one of these elements may become a limiting factor in plant health.
 
Regular feeding is needed to avoid stunted growth and reduced cropping.
pH 6.0 to 6.5
 
Before planting, irrigate the media with nutrient solution to achieve an EC of 5.0 mS/cm. maintain this feed strength for about a month and then decrease it gradually to 3.0 mS/cm over the next 8 weeks, then to between 2.0 and 2.5 mS/cm over the summer.
 
The ratio of potassium to calcium should stay at 3:2 throughout the life of the crop (N.B. some sources suggest a K:Ca ratio of 2:1).
 
Calcium to magnesium ratio should be 4:1.
 
Shortage of calcium can lead to blossom end rot and can affect the size of the fruit. Calcium is usually applied as calcium nitrate in the range of 250 to 500 ppm.
 
Potassium to nitrogen ratio should be 1.4:1` early in the crop but increased to 1.8:1 providing higher potassium later in the crop. Potassium is essential for good fruit quality, and higher levels can increase the fruits shelf life. Potassium levels can vary from 50 to 400 ppm without affecting yields, but higher potassium levels improve fruit quality such as dry matter and electrical conductivity of the juice, which enhances flavour.
 
Some growers use different concentrations of nitrogen for winter and summer crops, since tomato plants’ nitrogen requirements can vary significantly between winter and summer.
Phosphate should be relatively low, at about 40 ppm throughout the crop. High phosphorus levels (over 100 ppm) can result in iron deficiency
 
Sodium and chlorine levels should be kept as low as possible.
 
Trace elements are normally supplied in the following amounts, irrespective of the stage of growth:
 
Iron 1.00 ppm
Manganese 0.50 ppm
Zinc 0.40 ppm
Boron 0.30 ppm
Molybdenum 0.05 ppm 
Copper 0.05 ppm
 
 
Iron is important in hydroponic tomato cultivation. Some sources recommend iron levels of up to 5 ppm. Iron is added in the form of iron sulphate or as chelates containing iron. The chelate form is often preferred since the iron remains in solution and is relatively available over a wide pH range. The most popular compound is EDTA, but use of this molecule may be restricted or prohibited in some countries because it does not break down in the environment, and has the potential to contaminate natural waters. Iron deficiency in nutrient solutions is one of the most common problems in container production of tomatoes. Symptoms can develop slowly and growers need to be constantly observant.
 
Zinc levels are critical (below 0.25 ppm can cause deficiency and above 1 ppm can cause toxicity).
 
 
 
Suitable Systems
 
NFT is the most commonly used method throughout the world.
Multi-level NFT has shown great potential for increased production (in Poland).
Under NFT systems the size of fruits decreases towards the bottom end of a channel (hence total production is decreased).
 
 
Aggregate culture – Sutherland reports excellent results in most aggregate culture at 15 cm depth. Growing tomatoes in pots is an easy and effective culture method and is widely used, both in the industry and by amateur growers. A variety of media have been used successfully including Perlite, rockwool, sand, and gravel. Some media are more effective than others and Perlite seems to be a good all round choice with many advantages – such as its reusability, its absorbency and its drainage capacity.
 
Rockwool is used commercially in the Netherlands and also has many advantages.
 
 
 
Planting
 
Germinate seed in rockwool propagating blocks, or in vermiculite or perlite seed raising mixes, and transplant into your system.
 
 
Special cultural techniques
  • Prune out side shoots until flowering commences.
  • Trellising is necessary.
  • Bees may need to be introduced for pollination in larger scale greenhouse crops. Other methods, such as mechanical vibration of plants, have also been used in greenhouse production to achieve optimum pollination.
 
 
Problems
 
Blossom end rot is encouraged by any stress on the plant. Such stresses include irregular growth rate, inadequate oxygen levels around the plant root zone (resulting from poor nutrient solution or from heating of nutrient solutions), disruptions to supply or balance of the nutrient solution, and inadequate plant uptake of calcium. It is worth noting that while calcium deficiencies are a direct cause of blossom end rot, a variety of factors (including the amount of dissolved oxygen and the temperature of the solution) can prevent tomato uptake of calcium from nutrient solutions, so addition of more calcium will not necessarily rectify the problem.
Birds will attack ripe fruits.
 
Pollination can be a problem in a greenhouse (wind and insects normally contribute towards pollination) various technologies have been utilised in greenhouse tomato production to overcome this pollination problem.
Don’t smoke near tomatoes. A virus carried in tobacco can infect the plants.
 
Other pests include aphis, fruit fly, potato beetle, corn earworm, leafminer, white fly and mites.
Other diseases include anthracnose, bacterial canker, bacterial spot, blight, fusarium wilt, verticillium wilt and leaf mould.
 
 
 
Harvest and post harvest
 
Can be harvested green or firm and pink. Fruit should be handled with care to prevent bruising or skin breakage. Damage can still be done when fruit are green, although it may not become evident until fruit starts to ripen. The main mechanical damage encountered in commercial tomato crops is bruising or skin breakage from impact, vibration or compression.
 
 
Firm ripe tomatoes should be stored at 7 to 10 degrees C with 70 to 80% relative humidity and reasonable ventilation. Storage at temperatures above this will increase respiration rates of harvested fruit and decrease shelf life.
 
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