Hydroponics is the method of indoor gardening where plants are grown in nutrient water instead of soil. Tomatoes are a common plant grown indoors, as the hydroponics growing method provides flavorful fruit throughout the year.
Heirloom tomatoes are easily grown in a hydroponics system; however the light, temperature and nutrient value of the water must be monitored closely in order to produce the sweet tasting fruit that is characteristic of heirloom varieties.
Start heirloom tomatoes from seed or purchase seedlings. Start seeds by placing one seed in a rockwool cube that was soaked in water. Place the cubes in a covered tray and set it in a warm location. Remove the cover once sprouts appear and place the tray under artificial lights for 12 hours a day.
Transplant the tomato seedlings to a hydroponics system once a set a true leaves appear and roots are visible through the bottom on the cubes. This occurs in approximately 10 to 14 days.
Plant the seedlings in netted pots or larger rockwool cubes, depending on the type of hydroponics system being used. The small starter rockwool cube does not need to be removed from the seedlings. Space tomato plants 10 to 12 inches apart in the hydroponics system.
Monitor the water pH level to make sure it remains at 5.8 to 6.3 to prevent nutrient deficiencies in the tomato plants. Add potassium hydroxide to increase the pH number or phosphoric acid to lower the pH number. These additives are available at garden supply stores that sell hydroponics growing supplies.
Add a high potassium nutrient mix to the water to feed the plants. This is the preferred type for heirloom tomato varieties.
Place the hydroponics system under artificial metal halide lights. Mature tomato plants require 16 to 18 hours of light for maximum fruit production.
Place a thermometer in the growing area to verify the daytime temperature is 70 to 80 degrees F and the nighttime temperature is 60 to 70 degrees F.
Test the electrical conductivity (EC) of the water once the fruit is set on the plant. EC testers are available at garden supply stores that sell hydroponics supplies and are similar to a pH tester. The EC test will verify the total nutrient amount in the water. Heirloom tomatoes should have a reading of 3.5 or higher to produce a flavorful tomato.