Learn how to do anything: How to Grow Hydroponic Tomatoes

Hydroponic tomatoes are grown in a nutrient solution rather than soil, although they are typically placed in a non-soil material that can support their roots and hold the nutrients. Growing tomatoes hydroponically allows the grower to raise them in a controlled environment with less chance of disease, faster growth, and greater fruit yield. However, hydroponic gardening is much more labor intensive, and sometimes more expensive, than ordinary tomato planting, especially if you have not set up or run a hydroponics system before.

Steps

Setting Up a Hydroponics System

Decide which type of system to use. There are several varieties of hydroponic systems, and tomatoes can grow well in any of them. The instructions in this section will teach you how to construct an ebb and flow system, which is relatively cheap and easy to build.^[1] However, you may wish to investigate alternatives, such as the simpler "water culture" system suitable for cherry tomatoes and other small plants, or the more complex "multi flow" or "NFT" systems, which are more commonly used by commercial growers.^[2]
- Note: Hydroponics stores and home improvement stores may sell a hydroponics kit which includes everything you need to set up your system. Alternatively, you can purchase each component separately, or even find some of them around your house. Clean secondhand or previously used components thoroughly before building the hydroponics system.
Find a suitable location. Hydroponics systems are only suitable for indoor or greenhouse environments. They require precise control to function properly, so they should be set up somewhere closed off from other rooms and from the outside. This allows you to set the temperature and humidity to accurate levels needed for best growth.
- It is possible to grow hydroponics using natural light, but keep the system under a glass or polyethylene covering such as a greenhouse roof, not open to the air.
Fill a large, plastic container with water to use as a reservoir. Use a plastic container that does not let in any light to prevent the growth of algae. The larger this reservoir, the more stable and successful your hydroponics system will be. At minimum, each small tomato plant (such as cherry tomato plants) will require 1/2 gallons (1.9 liters) of water, while most, somewhat larger tomato plants will require 1 gallon (3.8L) each. However, many factors can cause the tomato plants to use water faster, so it is recommended that you use a container that can hold double the minimum amount of water.^[3]
- You may use a plastic bucket or trash can for this purpose. Use a brand-new one to prevent any contamination of the system, or at least a lightly-used one thoroughly scrubbed with soapy water and rinsed.
- Collected rainwater may be better suited for hydroponics than tap water, especially if your tap water is especially "hard" with high mineral content.^[4]
Fix a tray in place above the reservoir. This "ebb and flow tray" will support your tomato plants, and will be periodically flooded with nutrients and water that the tomato roots will absorb. It must be sturdy enough to hold up your plants (or be placed atop additional support), and placed higher than your reservoir to allow excess water to drain down into it. These are typically built of plastics, not metal, to avoid corrosion that could affect the plants and wear out the tray.
Install a water pump inside the reservoir. You can purchase a water pump at a hydroponics store, or use a fountain pump found at home improvement stores. Many pumps will have a chart listing the water flow at different heights. You may use this to find a pump strong enough to send water from the reservoir to the tray containing the plants. The best course of action, however, may be to pick a powerful, adjustable pump and experiment with the settings once you have your system set up.
Install fill tubing between the reservoir and the tray. Using 1/2 inch (1.25cm) PVC tubing, or the type of tubing that came in your hydroponics kit, attach one length of tubing between the water pump and the tray, so the tray can be flooded to the height of the tomato plant roots.
Install an overflow fitting leading back to the reservoir. Attach a second length of PVC tubing to the tray with an overflow fitting, located at a height near the top of the roots, below where the tomato plant stems will be. When the water reaches this level, it will drain back through this tube and into the reservoir.
Attach a timer to the water pump. A simple timer intended for light fixtures can be used to power the water pump at regular intervals. This needs to be adjustable so you can increase or decrease the amount of nutrients delivered depending on the plants' stage of life.
- A heavy duty 15-amp timer with waterproof cover is recommended.^[5]
- Any water pump should have a way to attach a timer, if it doesn't come with one already, but the exact instructions vary by model. Ask the manufacturer if you are having trouble with this step.
Test the system. Turn on the water pump and see where the water goes. If a stream of water fails to reach the tray, or if excess water spills over the edges of the tray, you may need to adjust the settings of your water pump. Once you have the water set to the correct strength, check the timer to see if it sets the pump going at the specified times.

Growing the Tomatoes

Grow tomato seeds in a special material. Raise your tomato plants from seed whenever possible. If you bring plants in from the outdoors, you may introduce pests and diseases to your hydroponics system. Plant seeds in a nursery tray with a special support material for hydroponics, instead of ordinary soil. One inch cubes of a material called "rock wool" is a common choice, as is lava rock or long strands of coco peat.^[6] Before using, soak the material with pH 4.5 water. Plant the seed under the surface, and keep under plastic domes or other transparent material to trap moisture and encourage the seeds to sprout.^[7]
- Gardening stores have pH test kits which allow you to measure the pH, or acidity, of your water, as well as pH modifier materials or kits that allow you to adjust it.
Place seedlings under artificial light once they sprout. As soon as the plants sprout, remove the covering and place the seedlings under a light source for at least 12 hours a day.^[8] Only use incandescent light bulbs as a last resort, as these produce more heat than other options.
- See the section on hydroponics system setup to learn about grow light options.
- Take care not to let the light shine on the roots to avoid damaging them. If roots are protruding from the starter material before they are ready to transplant, you may need to soak additional starter material and use it to cover them.
Move seedlings into the hydroponic system. Wait until their roots start to protrude from the bottom of the nursery tray, and the first "true leaf" has grown, larger and different in appearance than the first one or two "seed leaves". This usually takes 10–14 days.^[9] When you move them into the hydroponics system, you may place them at 6 inch (15cm) intervals in a layer of the same material, or transfer them to individual plastic "net pots" containing the same material.
- If using the ebb and flow system described in this article, the plants are placed on the tray. Other systems may call for the plants to be placed in a trough, along a slope, or wherever the water and nutrients can reach the roots.
Set the water pump timer. To begin with, try setting the pump to run for 15 or 30 minutes four times a day (once every six hours). Keep an eye on the plants: you'll need to increase the watering frequency if they begin to wilt, and decrease it if the roots become slimy or soaked. Ideally, the material the plants are in should just barely dry out when the next watering cycle comes along.
- Even once the watering cycle is established, you may need to increase the watering frequency once the plants begin to bloom and fruit, since these processes require additional water.
Set your artificial lights (if applicable). For ideal growing conditions, expose growing tomato plants to between 16 to 18 hours of light a day. Then turn off the lights and let them sit in total darkness for about 8 hours. The plants will still grow if you are relying on sunlight, but will likely grow more slowly.
Stake and prune tall tomato plants. Some tomato plants are "determinate," meaning they grow to a specific size, then stop. Others continue to grow indefinitely, and may need gently tying to a stake in order to grow upright. Prune them by breaking off stems with your hands rather than cutting them off.
Pollinate the tomato plant blossoms. When the tomato plants bloom, since there are no insects in your hydroponics environment to pollinate them, you will need to do it yourself. Wait until the petals bend back to expose the round pistil and the pollen-covered stamens, or long, thin sticks at the flower center. Touch a soft paintbrush to each of the pollen-covered stamens, then touch the rounded end of the pistil. Repeat daily.

Creating Good Growing Conditions

Control the temperature. During "daylight" hours, the temperature should be 65 to 75 degrees Fahrenheit (18 to 24 C). At night it should be 55 to 65 degrees Fahrenheit (12 to 18 C).^[10] Use thermostats and fans to regulate the temperature. Monitor the temperature while the plants grow, as it could change with the climate or tomatoes' life cycle.
Run a fan in the room (optional). A fan that exhausts to the outside or another room may help keep the temperature even throughout the room. The air flow it creates may also make pollination easier, although to be certain of growing fruit you may wish to pollinate by hand anyway, as described below.
Add a nutrient solution to the reservoir of water. Choose a nutrient solution made for hydroponics, not ordinary fertilizer. Avoid "organic" solutions, which may decompose and make caring for your system more complicated.^[11] Because the needs of your system vary with tomato variety and mineral content of your water, you may need to adjust the amount or type of nutrient solution you use. To begin with, however, follow the instructions on the packaging to determine how much you need to add to the reservoir.
- Two part nutrient solutions create less waste and can be adjusted if problems arise simply by mixing them in different amounts, making them preferable to one-part solutions.^[12]
- You may wish to use a growth-focused formula while the tomatoes grow, then switch to a bloom formula once they flower to meet their new nutrient needs.
Use a pH test kit to adjust the water. Use a pH test kit or litmus paper to test the pH of your nutrient and water mix once it's had time to become an even mixture. If the pH is not within the range of 5.8–6.3, ask a hydroponics store or gardening store employee about materials that can be used to lower or raise the pH.
- Phosphoric acid can be used to lower pH, while potassium hydroxide can be used to raise it.
Install grow lights (recommended). Artificial "grow lights" will allow you to simulate ideal growing conditions year round, providing your tomatoes with many more hours of "sunlight" than the garden outside may be receiving. This is one of the major benefits of an indoor growing system. However, if you are using a greenhouse or other area that receives high amounts of natural light, you may accept a shorter growing season and save money on electric bills.
- Metal halide lamps simulate sunlight most accurately, making them a popular choice for hydroponics systems. Fluorescent, sodium, and LED grow lights are also available, but may cause slower or differently shaped growth. Avoid incandescent lights, which are inefficient and short-lived compared to other options.^[13]
Monitor the water regularly. An electrical conductivity meter or "EC meter" may be expensive, but it is the best way of measuring the concentration of nutrients in the water. Results outside the range of 2.0–3.5 indicate that the water should be changed or partially changed.^[14] If you do not have an EC meter, look for the following signs in your tomato plants:^[15]
- Leaf tips curling downward may mean the solution is too concentrated. Dilute with pH 6.0 water.
- Leaf tips curling upward or a red stem suggest the pH is too low, while yellow leaves indicate the pH is too high or the solution is too dilute. In any of these scenarios, change the solution as described below.
Change the water and nutrient solution regularly. If the water level in the reservoir drops, add more water, but do not add more nutrients. Every two weeks, or once a week if your plants do not look healthy, empty the reservoir completely and rinse the support material and roots of the tomato plants with pure, pH 6.0 water to leach away mineral buildup that could cause harm.^[16]^[17] Fill the reservoir with a new water and nutrient solution, making sure to balance the pH and let the mixture become even before you start the water pump.
- You may use the water used for leaching to water regular garden plants.