There has been a great deal of money spent researching and growing hydroponic tomatoes commercially, so it makes sense to follow the lead of the commercial growers. By and large, most commercial growers are using various forms of drip irrigation hydroponic systems and growing tomatoes in either rock wool slabs or perlite.
The process is similar regardless of the container or growth medium used.
- A drip line is used to supply nutrient solution, on either a continuous or intermittent basis, to the base of the plant.
- Approximately 1-1.5 inches of nutrient solution is maintained in the bottom of the growing container which is normally around 7 inches deep.
- Adequate drainage is supplied to allow all but the 1-1.5 inches of nutrient solution in the bottom of the growing container to return to the nutrient solution reservoir where it can be re-circulated.
- Nutrient solution is tested/maintained and periodically flushed and replenished. Flushing the system with pure water periodically also helps to leach excess salts from the growing medium.
Success can be had, particularly with smaller varieties of tomatoes using high tech aeroponic systems and many home growers have good results with various flood and drain systems; but in keeping with what is being done for commercial production, the most common method employed for large plants in home systems generally involves some type of drip irrigation. 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.
There are many good options for starting this type of growing system in the home or small farm garden.
Build Your Own System
Fortunately for those on a budget, or who just want to have a more intimate relationship with their growing system, there is some excellent guidance available for building your own system for growing hydroponic tomatoes. This is a good article that discusses how to build your own hydroponics system. There are also many inexpensive books that contain details for several relatively easy to build systems.
Tower Drip Systems
There are several companies marketing tower growing systems. These systems use some sort of vertical arrangement where the nutrient solution can flow from the top set of growing containers through each level and finally to a reservoir at the bottom of the tower. These systems are worth looking into and may be particularly valuable where garden space is at a premium. When shopping for such a system, be aware that some towers are NFT Systems and not designed for growing in medium. Also, some of these systems are not designed with a re-circulating pump and reservoir and require some means for supplying adequate irrigation to the top pots and dispensing of, or re-circulating runoff from the bottom.
Starting Tomato Plants
Many hydroponics growers prefer to start plants from seed to avoid any possible pest or disease contamination from nursery stock. Rockwool cubes are a good choice for seed starting rather than using organic substances like peat that will then decompose causing possible problems when placed in the growing medium. The one-inch rockwool cubes can be arranged in standard nursery trays with pre-fit plastic domes, or any suitable tray can be covered with cellophane kitchen wrap to help maintain a mini-greenhouse environment for seed germination. When using rockwool for seed germination, or as a growing medium, make sure to presoak with water adjusted to a pH of 4.5 prior to planting. It is important to provide adequate natural or artificial light to your seedlings as soon as they sprout to avoid lanky, weak plants. Once sprouts have bolted in search of light, the process cannot be reversed, and week adult plants will result. Generally, in a couple weeks the sprouts will be showing their first true leaves and will be ready to be transferred into their permanent home in the growing medium.
Commercial hydroponic tomato growers use rockwool more than any other growing medium and Perlite is probably a close second. This said, great results are also possible using other forms of medium including various brands of expanded clay, pine bark, coconut coir or combinations of the above. There are also some new growing mediums coming on the market that may offer some advantages and are worth a look.
Regardless of the technique used to grow tomatoes, several factors are important for successful harvests.
The lighting that tomatoes receive will have a significant impact on growth and fruit production. Many people mistakenly believe that because tomatoes do well when days are long that they prefer intense light. On the contrary, particularly in the southern latitudes and summer months in all latitudes, tomatoes do better with partial shade and/or defused light. When tomatoes are grown outdoors, or in a greenhouse setting, ideally partial shade should be provided after noon when the sunlight is most intense.
Tomatoes will have maximum fruit production with 16-18 hours of light, but they may also do best with 8 hours of total darkness each day. If you are growing tomatoes in a greenhouse for year-round production or an extended season, or indoors under entirely artificial light, 16 hours of light each day is a good target. The quality of artificial light is as important as the quantity. Tomatoes do best if supplied with full spectrum lighting throughout their growth cycle. If providing artificial light, search for lights that provide both blue and red spectrum light.
Nutrient Solution Considerations
Two important factors concerning the nutrient solution are pH and (EC) electrical conductivity. It is critical that water used to mix nutrient solution for tomatoes be adjusted to a pH of 5.8-6.3. Once the correct amount of pH up or pH down solution needed to adjust tap water is determined by using an inexpensive pH test meter, this same amount can be used each time pH adjusted water is needed. EC measures the total dissolved solutes in the solution and gives an indication of the nutrient level. The optimal rate for tomatoes is 2.0-3.5. Quality nutrient solutions will have mixing instructions that will provide the proper nutrient level. Generally, the best results can be had by using a quality growth formula until the plants are near the flowering stage and then switching to a bloom formula.
For small systems it is recommended that the nutrient solution be changed, and the system flushed with pH adjusted water each week. This is accomplished by draining the reservoir of used nutrient solution, running pure pH adjusted water through the system and then draining this and adding freshly mixed nutrient solution. The used nutrient solution and the leaching water can be used to water other soil-based plants. This process will help to leach excess salts from the growing medium and ensure proper pH and nutrients are maintained.
Tomatoes are a warm weather plant and do not do well when the air temperature dips below 50 degrees (Fahrenheit). The optimum temperature for tomatoes is 70-85 degrees during the day and 65-70 at night. In greenhouse settings these optimum temperatures can be maintained, or tomatoes will do quite well at a constant 75 degrees. Many outdoor growers like to start plants inside several weeks before outside temperatures are optimal to get a jump on the season. This is good practice, but care must be taken not to set plants outdoors too soon. Plants subjected to cold conditions may never fully recover and be poor producers.
Tomatoes are very well suited to hydroponic growing, particularly using top feed drip systems. For soil-based gardening enthusiasts wanting to give hydroponics a try, starting a small hydroponic tomato growing system may be just the thing to wet the appetite this season.
John Berends is a horticulture lover and freelance writer.