Article 3-5 I Have Tomatoes

by Cindy Rae, Compliments of Homegrown Hydroponics

Imagine that first bite of a sweet, succulent, ripe tomato picked fresh from your garden. The warm juice runs down your chin as a delightful explosion of flavour awakens dormant tastebuds. In our harsh climate, fresh tomatoes can usually be enjoyed for only a few short weeks of the year. Then it’s back to artificially ripened, flavourless imports your grocer charges a small fortune for. Take heart, you can savour the homegrown tomato experience year round.

Tomatoes grown hydroponically, indoors under lights, are equal to, or superior in flavour and nutrition than their outdoor, soil grown counter-parts. A tomato’s sweetness and flavour is largely dependent on light and temperature. The nutritional value of a tomato is dependent on the nutrition the plant receives while growing and producing fruit. In the controlled environment of an indoor garden, the plants exact requirements can be met with artificial lighting, temperature control and supplemental nutrition. This enables the grower to enjoy a continuous harvest all year long without sacrificing taste and goodness.

Hydroponics is a pure, clean method of cultivation. For this reason it is recommended you start your tomatoes directly from seed. Bringing plants in from outside creates a potential for pest and disease contamination. Start seeds in one inch rockwool starter cubes in a standard nursery tray with dome. Rockwool cubes should be pre-soaked in water adjusted to a pH of 4.5 prior to planting. Keep covered tray in a moist, warm (20-25°C) environment until seedlings begin to sprout. Once vegetation appears, immediately move the seedling into a light source, metal halide or flourescent lights, for at least 12 hours per day and remove domes. Failure to provide light soon enough will cause seedlings to bolt in search of a light source. Ensure roots are never exposed to the light as this will cause damage and death to the roots and delay plant growth.

Once true leaves appear and roots are showing through the bottom of the starter cubes, usually around 10 – 14 days, seedlings are ready to be transplanted to their hydroponic garden. There are several different hydroponic methods used for cultivating tomatoes indoors. Space restrictions, type of tomato and plant size all have to be considered when choosing a system.

The most common method employed for large plants is the drip irrigation system. In this fully automated, re-circulating system nutrient solution is pumped from a reservoir, fed to the plants through drip emitters and allowed to drain back to the reservoir by gravity. In order to create gravity flow the grow unit must be placed higher than the nutrient reservoir. The nutrient is continuously circulated during light-on hours. For the home hobbyist we recommend using the expando system. This consists of an individual pot for each plant, linked to the nutrient reservoir by 1/2″ tubing. Heydite, small, reusable porous rocks are used as the growing medium providing excellent aeration to the roots. The one inch cube containing the seedling is transplanted directly into the pot and covered with heydite. The constant feeding allows the root system to develop in minimum space resulting in higher yields.

Drip irrigation can also be done with rockwool, a technique favoured by commercial growers. The starter cube and seedling are placed in the premade hole of a three or four inch rockwool cube which is placed on slabs of rockwool in a trough. The roots will grow down through the cubes and into the slabs. The troughs should be slightly wider than the slabs to allow room for the nutrient solution to drain back to the reservoir. Tomato plants should be spaced about 10 to 12 inches apart or four plants per slab.

With both techniques the size of reservoir and pump will be determined by the number of plants. Irrigation will need adjusting as the plants grow, allow for four liters of nutrient solution per day for mature plants, smaller seedlings will consume less. The nutrient reservoir should be changed once a week. Choose a pump with a high enough gallons per hour rating to adequately reach the plants farthest from the reservoir. Emitters can become clogged with salts from the nutrient solution and should be watched closely and cleaned when necessary.

Ebb and flow or “flood and drain” tables are another excellent method used for cultivating tomatoes. Tables range in size from 1′ X 2′ to 4′ X 8′ and can accommodate many plants in a small area. For cherry tomatoes or smaller determinate varieties, deep water culture may be used. Complete hydroponic gardens sold as kits are usually deep water culture and available in many shapes and sizes and are excellent for the novice hydroponic gardener.

No matter what technique you choose, there are several growth influencing factors (GIFs) to consider. The most important GIF is light. Artificial metal halide light can simulate full summer sunlight when daylight is at it longest. At maturity, tomato plants require a 16-18 hour photo-period to ensure maximum fruit production and an eight hour respiration period of total darkness. Gradually introduce your plants to higher light levels by moving the bulb closer to the plants by an inch or two every few days.

pH is the measure of alkalinity or acidity of the nutrient solution and is another very important GIF. If pH levels are not maintained at the appropriate level (pH 5.8 – 6.3 for tomatoes) nutrient deficiencies and toxicity will occur. Even seemingly small fluctuations in pH levels can result in inferior nutrient uptake by the plant. pH will need to be adjusted up or down based on the original reading of your water source. Potassium hydroxide will raise pH while phosphoric acid will decrease pH levels. Both products are available at your local hydroponic retail store. pH can be influenced by other factors and must be monitored regularly and adjusted as necessary.

Electrical conductivity (EC), measured in milliMhos, is the measure of electrical conductance of the total dissolved solutes (minerals) in the solution. The optimum EC range for tomatoes is 2.0 to 3.5 milliMhos. While EC measures the total dissolved minerals in a solution it does not identify the amounts of specific elements present. Therefore, it is easier to achieve the ideal EC using premixed 2-part hydroponic nutrient formulations than attempting to create your own formula using individual components.

Temperature is also an important GIF however, it is quite easily controlled. Tomatoes, like most plants grow best with a day/night temperature differential based on light or daytime perception. When there is light the plant considers it daytime and the temperature should be adjusted accordingly. The ideal daytime temperature for mature tomato plants bearing fruit is 18 – 25°C and nighttime is 12 – 18°C. An independent thermostat should be placed among your plants to ensure temperature regulation. An exhaust fan will help control temperature and provide air exchange.

Plant nutrition is the basis for hydroponics and holds the key to the nutritional quality of your tomatoes. There are a wealth of pre-mixed nutrients available, however when determining which nutrient to use, look for a product that is especially formulated for hydroponic use. A 2-part formula will eliminate binding, solidification and waste of mineral elements, which occurs with ordinary 1-part plant foods.

Close observation of any changes are critical when growing hydroponic tomatoes. Early diagnosis and adjustment of nutritional disorders is crucial as they rapidly increase in severity and spread quickly.

  • Check the colour of the leaves; yellow leaves may indicate that the nutrient solution isn’t strong enough or pH is too high, locking out nitrogen – leach and change the solution.
  • Leaf tips curl up or red stem may indicate a magnesium deficiency caused by too low a pH – leach and change solution
  • Leaf tips curling under may mean the nutrient level is too high – add pH 6.0 water
  • A potassium deficiency my cause flowers to fall off before setting fruit – leach and change solution.

Blossom-end-rot caused by too much water puddling in the root zone will create a calcium deficiency – leach and foliar spray with a calcium nitrate solution.

Leaching should be done at every reservoir change to avoid encountering problems. This will rid the growing medium and root zone of toxic salt build up. To leach, rince the root zone with straight pH balanced water. Use twice as much liquid as the hydroponic container would have held when empty.

These are some basic nutritional disorders however, they are easily avoided by using a good 2-part fertilizer, maintaining a correct pH and changing your solution regularly.

Tomatoes are pollinated outdoors by the wind, bees and other insects which carry the male pollen to the female part of the flower (stigma.) Indoors pollination must be performed manually by the grower. This can easily be accomplished using a small paint brush or q-tip to transfer the pollen. Simply dab the brush or q-tip on the stigma of each flower. This is best done daily over a period of several days when the flowers indicate their readiness to receive fertilization by bending their petals back and exposing the stigma.

Tomato plants are quite brittle and require gentle handling when pruning and staking. Use plastic twine or a plant yo-yo to encourage and support vertical growth and bear the weight of the fruit. Removing side shoots and suckers that grow between the main stem and leaf stems will further help train with vertical growth and eliminate unnecessary distribution of nutrients. Suckers should be gently broken off at their base by hand. Avoid the use of knives or scissors which can transfer diseases from plant to plant. As plants begin to produce fruit, the bottom leaves will start to yellow and dry out. Remove these leaves at the main stem of the plant to allow air flow and to prevent disease and infection.

A little bit of knowledge and patience will produce infinite rewards in hydroponic gardening. That first bite of juicy August tomato in the middle of January will be your stepping stone to a culinary adventure. Harvest all of summer’s pleasure’s indoors year round hydroponically, the homegrown way.