Hydroponic Tomatoes Indoor Grow Guide

Growing hydroponic tomatoes indoors

A beginners guide to growing hydroponic tomatoes under grow lights. In the following article we answer some of the most common indoor tomato growing questions.

What temperature should the grow tent be for hydroponic tomatoes?

Daytime 26°C - 28°C

Night 20°C - 23°C

What humidity should be maintained in the grow tent?

The best humidity for hydroponic tomatoes in a grow tent is 50-60%.

How long should the grow lights stay on during the "day time" in a hydroponics setup?

Vegetative phase of hydroponic tomato plants=18 hrs per day (first 4-5 weeks)

Flowering phase of hydroponic tomato plants=12 hrs per day (8-10 weeks)

What is the best distance between grow lights and tomatoes plants?

The gap should be approx. 40cm for 400W grow lights, 40 - 60cm for 600W grow lights and 60cm for 1000W grow lights.

A fan blowing gently between the hydroponic tomatoes and the grow lights will help stop the heat building up in the grow tent.

If using cool tubes the grow lights can be much closer. For 700W rated LED grow lights, 1.0m above to maximise the spread of light.

What is the best type of grow light to use in a hydroponic setup? High Pressure Sodium (HPS) vs Metal Halide (MH)

HPS grow lights outperforms MH grow lights when used for a whole grow and flower cycle of hydroponic tomatoes. HPS noticeably outperforms MH if it is used for the flower stage, but MH performs slightly better during the growth phase. For best results, use a MH for growth and HPS for the flowering phase of your hydroponic tomatoes.

How often should I change my hydroponic grow lights?

For best results change your grow lights in your hydroponic setup every 3000 hours (every 2 cycles using a single grow light). There is a 10% loss between 3000-4000hrs and a 25% loss from 4000 hrs usage.

Do I need reflective material on the walls of my hydroponic grow room? E.g. Panda film or Mylar?

You don't need mylar on the walls of your hydroponic grow room, but white, shiny and reflective walls means more light reflection onto the tomato plants which means more growth.

How much ventilation is necessary in a hydroponic setup?

Ventilation needs to be enough to maintain the right temperature and humidity of around 50% in the centre of the canopy of hydroponic tomatoes. The tomato plant leaves should maintain a slight flutter during daylight hours. Generally, it is better to have too much rather than too little ventilation to raise CO2 levels for your tomato plants. Technically, you should be looking to replace the volume of air in the grow tent every 3 to 5 minutes.

What brand of hydroponic nutrients should I use?

All hydroponic nutrients will grow hydroponic tomatoes. But some will be easier to use and less maintenance than others.

What EC should I aim for with hydroponic tomatoes? (Electrical Conductivity measures the salts in the water)

The EC (Electical Conductivity) of hydroponic tomatoes changes with the growth phase and the grow media. It is also different for each brand of hydroponic nutrients. Some hydroponic grow media like Canna Terra already have nutrients in them, so the EC can be lower for the first month of the grow.

A general guide to hydroponic EC:

Vegetative: 1.1 - 2.0 EC

Flowering: 1.8 - 2.3 EC

For the last week: 0 - 0.4 EC

To measure your EC, you will need an EC/TDS pen.

What pH should I maintain for hydroponic tomatoes? The safe range is 5.5 - 6.5, above or below this the plant will not absorb some of the minerals from the hydroponic nutrient. The ultimate level for plant absorption is between 5.5 - 5.8. this is when all the minerals are available at full strength. In the last 3 weeks of flowering us pH of 6.2 - 6.8. This will make more P/K available to your plants. What is the difference between a recirculating hydroponic systems and a run to waste (RTW) system?

Recirculating hydroponic systems work by pumping the hydroponic nutrient solution from a reservoir to the tomato plant and then through a drain hole back into the reservoir. The same water is used over and over though the reservoir is occasionally topped up or the water is replaced to replace the water and hydroponic nutrients used by the tomato plants.

Run to waste (RTW) hydroponic systems work by pumping the hydroponic nutrients from the reservoir to the tomato plant. The water and nutrients are taken up by the plants roots and any excess that flows out of the bottom of the pot is discarded. Growing in coco is an example of a RTW hydroponic system.

How often should I water in a Perlite growing media?

The amount of irrigation water to apply is probably more important than how and when to irrigate. A general rule of thumb to follow in irrigating plants is to apply 10-15% more water than the container will hold. Frequency of watering depends on tomato plants size and temperature, but will vary from once or twice daily immediately after transplanting, to several times per day on warm days during harvest. Only water the plants during the day period.

How often should I water in an Expanded Clay Ball growing media?

A general rule of thumb to follow in irrigating is to apply 10-15% more water than the container will hold. Frequency of watering depends on plant size and temperature, but will vary from one 15min feed every hour while the lights are on during the first weeks of growth, then one 15min feed every two hours. Start a few minutes before the lights turn on, and only water the plants during the day period.

How often should I water in a Coco growing media?

If you are using a pot over 30L water once per 24hrs until the plant reaches 30cm wide/high, then 2 feeds till 50cm wide/high before running the maximum of three feeds.

IMPORTANT: around 20% runoff is a good amount, a good rule of thumb is to wait a couple of minutes as the coco acts like a sponge then lets out the excess.

If the pots are smaller than 30L then it may be necessary to water up to 5 times per day. Only water during the day period. Do not over water the plants as this will slow growth and cause pest and disease infestation.

Is it necessary to aerate the hydroponic nutrient solution?

Yes, aerating nutrients is a good idea as it improves hydroponic tomato plant health by adding oxygen to the system and protects against stagnant water.

What temperature should my hydroponic nutrient solution be?

Hydroponic nutrients should be between 18°C - 22°C. If the solution is too cold use a water heater. If it is too hot use a nutrient chiller or cooler.

How often should I flush hydroponic tomatoes?

Every 7-10 days is recommended for hydroponic tomatoes. A small amount of hydroponic nutrients in flush solution (EC 0.6) will save the tomato plant from any unnecessary stress. Make sure temperature and pH of the flush water is correct. Do not over flush as this can cause inconsistent PPM/EC/CF levels. A general guide is half the volume of water to the amount of media in the pot. Eg 50L pot=25L of flush water.

What causes the tips of hydroponic tomato plants to burn?

Burnt tomato plant tips can be caused by too much fertiliser (too high EC), too much salt in the water, not enough water, grow lights too close or not regular flushing. Certain hydroponic nutrient deficiencies can also cause leaf tip burn.

What causes hydroponic tomato leaves to turn yellow?

Yellow leaves on hydroponic tomatoes can be caused by number of things:

  1. Hydroponic nutrient solution too warm (18-22C is optimum)
  2. Low oxygen levels in hydroponic nutrients due to lack of aeration
  3. Over watering
  4. Onset of root disease
  5. The pH is too high
  6. Too much salt in the water
  7. Grow room temperature is too high or too low

All of these stop the plant from taking up nutrients in the correct quantities and balance.

Why do hydroponic tomato plants stretch? Hydroponic tomato plants stretch when the grow light is insufficient or the grow tent humidity is too high. Lack of grow tent ventilation is normally the cause of high humidity but it can also be cause by too many tomato plants in a small area. A larger ventilation fan may help to fix this.

Why are the roots brown on my hydroponic tomatoes?

Brown roots on hydroponic tomatoes have usually been attacked by disease, probably pythium. Using Fongarid will be of great assistance and usually eliminates the problem.

Another frequent cause is over watering.

Healthy roots will be white. (Products that can ensure this are Rhizotonic and Cannazym or House & Garden Roots Excelurator and House & Garden Multizym).

My hydroponic tomatoes have very small bugs that spin webs, what are they?

These are Red Spider or "Spider Mite". They can cause severe damage to hydroponic tomatoes and should be treated by spraying tomato plants when small to prevent an infestation happening. Mite rid or Spray safe are suitable. If it is late in the flower stage then Mite Aerosol will be more suitable as this is a dry spray.

There are small black flies around the edges of my tomato pots in the coco around the root system of my hydroponic tomatoes. Are they a problem?

Yes, Scaria fly can KILL a tomato plant easily if untreated. These flies are also known as fungus gnats. Their larvae chew on and devour the fine root hairs of your tomato plants; this damage increases the risk of waterborne diseases such as Pythium. Eradicator or Scarid 10 are very effective for the treatment of Scarid Fly. Fongarid will be required to treat for the disease left after the Fungus Gnats.

What is the brown rotting in the flower buds of hydroponic tomatoes?

This is nearly always a disease called Botrytis (grey mould).To help prevent this you can use products like Silikamagic or Bloom Silica. If you have this then Canadian Express PMT will stop the rot spreading through the tomato flowers.

What are the white powdery spots on the leaves of my hydroponic tomatoes?

This is most likely a disease called powdery mildew. Powdery mildew is a disease that spreads by airborne spores that enter the grow tent from the ventilation or when the door is opened. To prevent this try a bit more ventilation and if you have a severe case of powdery mildew try Canadian Express PMT. For a more detailed diagnosis feel free to contact us.