The Mammoth Guide to Growing Hydroponic Tomatoes

Note: This is a fairly involved guide that assumes you already have, or will be buying, an automated hydroponic system. If you’re new to hydroponics gardening and want a cheap way of getting started you may be better trying to grow lettuce.

When I first started this website, my goal was to create an in-depth hydroponics resource. Helping you pick out the perfect system just isn’t enough: I want to show you how to use it too.

That’s where the idea for this article comes from: a practical guide to help you get the most out of your hydroponic system, by giving you complete instructions from start to finish for how to grow a specific plant.

The plant I’ve chosen is the tomato. This is a very popular, versatile plant, used in many dishes all around the world. It’s also one of the first plants that many new hydroponic enthusiasts attempt to grow, making it an obvious choice.

And this is it – it’s been a labor of love, but it’s finally here: this is your one-stop shop for everything you need to know about growing tomatoes hydroponically. Enjoy!

Type of Hydroponics System

Tomatoes are fairly hardy plants, meaning they can be grown with almost every type of hydroponics system. This is great news for us growers: whatever system you have at home, you will be able to grow tomatoes with great results — far greater than what could be achieved by growing in soil.

9693268221_7b5f21cfa0_zHowever, as with most other plants, using a different type of system will produce different results: the setup of some types of systems is better suited to tomatoes than others. With this in mind, if you are looking to purchase a system specifically for growing tomatoes, this guide should come in handy. For those of you that might be unfamiliar with the terminology used, click here.

In my opinion, there are three types of hydroponics systems that are best suited to the needs of tomatoes.

The first is the Nutrient Film Technique (NFT). An NFT system pumps the nutrient solution from the reservoir onto a slightly downwards sloping growing area. The solution, now aided by gravity, will slowly trickle down the slope and back into the reservoir in a continuous cycle. The plants are suspended above the solution, their roots hanging down below, barely touching the slow trickle of nutrients. These systems are sometimes used commercially to grow tomatoes. Whilst NFT is effective, there can be problems with the plants higher up the growing area receiving more nutrients than the plants lower down (inevitably). There can also be problems with the roots becoming entangled too.

Next up, we have the “ebb and flow” systems. These are often used as home systems, preferred by many amateur enthusiasts due to their simplicity and cheap price. These systems work by pumping the nutrient solution up from the reservoir into the grow tray, periodically flooding it. After being flooded, the pump is turned off and the solution simply drains away (hence their alternative name: a “flood and drain” system). Whilst this setup can work well for growing tomatoes, and will always attract budget gardeners, the flooding part of a cycle means there is little way of refining how much of the nutrient each plant receives, and this does take away some of your control.

3158937163_78cb342bbb_mFinally, there’s the “drip” system: this is my preferred system for growing tomatoes, and I’ve witnessed an increasing trend of commercial hydroponics growers favoring this type of system. It works in a similar way to the “ebb and flow” system, however rather than simply flooding the grow tray, the nutrient solution is pumped along a network of tubes where it is “drip-fed” to individual plants, allowing you to fully customize your system to cater to the needs of each plant. I like to have as much control as possible in the growing process, and so this system suits my tomato growing needs perfectly, as well as having a little more elegance than a simple “flood and drain” system.

Best Hydroponic System for Tomatoes

Now we know that we are looking for a hydroponic “drip” system to grow our tomatoes, this helps us narrow things down a lot. In my opinion, there are two types of “drip” system that I would recommend above all others, and both are built by General Hydroponics.

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The WaterFarm System

Waterfarm IndividualThe WaterFarm is the “budget” drip system, and you can purchase it as either an individual tank, or as part of a system of eight.

The individual tank is obviously much cheaper, coming with a 4-gallon reservoir and a 2-gallon growing tray, so they’re not exactly small! The pack comes with everything you need, including some clay pebbles, which is a nice touch. General Hydroponics have recently improved the pump included in the system, and it now functions better, as well as representing better value for money.
Waterfarm 8
The 8-pack comes with eight of the individual tanks, but also features a central control tank with a 13-gallon reservoir and 8-gallon controller. As well as allowing you to grow eight times the quantity, this version of the WaterFarm also requires much less maintenance: with the individual system, you will have to regularly top up the nutrient levels as the plant absorbs them; however, with the 8-pack, the central control part of the system actually tops up the individual tanks with nutrients as required. The old solution, which overtime becomes toxic, is drained from the system too.

The best thing about the individual systems is that the tank is exactly the same as the ones used in the 8-pack. This means, if you decide at some point down the line that you want to increase your output, well, you can simply add the individual tank you already own to a bigger system! Put simply, your investment will never be wasted, as your tank can easily be included in a more complex system.

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The PowerGrower System

Powergrower IndividualLike the WaterFarm, the PowerGrower is also available as an individual tank, or as part of an 8-pack.

There are some similarities between the systems, but the PowerGrower is considered the better of the two. Each individual tank is around 50% bigger, with a 5.7-gallon reservoir and a 3-gallon growing chamber. The PowerGrower has a distinct hexagonal shape, which looks great and is very useful, as it allows you to grow more plants in the same surface area.
Powergrower 8
If you opt for the 8-pack, the central control system comes with a 17-gallon reservoir and a 17-gallon controller unit. To put it bluntly: this is one serious piece of kit, and this is a system that will last you a long, long time.

These systems also come with an “elite” air pump, and the difference is noticeable. You are getting a bigger system, with better components, and although the price is slightly higher, I believe the PowerGrower offers much better value. Whether you opt for the individual system or the 8-pack is up to you, but, as with the WaterFarm, all tanks can easily be installed into a larger system in the future.

Optimal Growing Conditions for Tomatoes

When you use a hydroponic system, particularly one kept indoors, you can control every aspect of the growing process. This allows you to manipulate conditions in a way that just isn’t possible with outdoor garden growing. The result: faster growing, more nutritious, better tasting tomatoes!

There are four areas that you should pay particular attention to:

Lighting

Tomatoes love light. Lighting is often ignored when it comes to growing tomato plants, but this is one of the most important factors of all: get it right and you’ll have a guaranteed supply of healthy fruit!

Try to set up your system in an area with a good source of light, whether this is indoors or in a greenhouse. Ideally, tomatoes should be in a well lit area for around 16 hours a day. If this is not possible, they require a minimum of 8 hours. If you are serious about growing a strong tomato yield, I would recommend investing in an LED grow light, which will allow you to directly control how much light the plants receive each day. In my opinion, hydroponic systems are all about having as much control as possible; therefore, purchasing a grow light would definitely be a worthwhile, and long-term, investment.

TaotronicsThere are some fantastic LED lights available on the market, but my preferred option will always be the TaoTronic grow light. They come in either a funky little UFO style 90 Watt variety, or a less glamorous, rectangular 120 Watt version. Both lights are capable of covering the full color spectrum, meaning you can choose the color of light your tomatoes need; however, if at a later date you want to use your grow light for a different type of plant, possibly one that requires very specific lighting conditions, this light has enough versatility to allow you to do so.

I would also add that the manufacturers estimated-lifespan for the product is 50,000 hours; this means that, if you run the grow light for the specified 16 hours per day, the light will last you for over 8 years! That’s fantastic value!

Grow Tents

Great, we’ve got a system that is capable of providing the tomato plant with as much light as it requires. Now, we need to turn our attention to the lighting at night. During the night, tomatoes prefer as close to total darkness as possible, for at least 8 hours. I realize that it can be quite difficult to find a spot around the home that is capable of providing total darkness. Thankfully, there are options available to help with this.

Lighthouse Grow TentI would advise you to look into investing in a grow tent. These are fabric tents that essentially create a closed off environment that acts as a grow room. I am a strong advocate of grow tents grow tents as they effectively segregate your plants from the outside world, allowing you to refine even further the growing conditions! Not only this, they also provide numerous other benefits, especially at night. Most grow tents are made from a thick fabric which, when closed, can block any light from getting to your plants. The interior of the tent is lined with a highly reflective material which works fantastically in conjunction with your LED grow light and allows you to get the maximum benefit from your lighting equipment.

My personal preference is the Lighthouse grow tents. Not only do they represent fantastic value, but they are incredibly simple to erect. I often struggle with this sort of thing, so a nice, logical set of instructions was perfect for me! The fabric is impressively thick and resilient, meaning it is unlikely to tear during setup. It’s also surprisingly light, meaning you will have no issues packing it away into storage.

I would also add that the Lighthouse tents come in a range of sizes, from the smaller end of the scale (32″ by 32″) all the way up to almost commercial sizes (120″ by 60″) and everything in between! This means you can select a grow tent to fit the size of your grow room, but (most importantly!) large enough to house your hydroponic system.

Temperature

20423119_4ea7dea8f8_mTomatoes are fairly hardy plants, meaning they can thrive in a wide range of temperatures. Generally, a temperature of 18°C to 25°C is desirable during the day, and a temperature of between 12°C and 18°C at night time.

Tomatoes can survive temperatures in excess of these for short periods of time, so if the temperatures are unpredictable I wouldn’t be too concerned. They are, however, warm weather plants, and it is better for the temperature to get too hot than too cold. If your tomatoes are exposed to frost, this can quickly kill them.

If you are worried about your grow room getting too cold, you have a second reason to invest in a grow tent. Because you’re creating a sealed environment you will find the heat doesn’t quickly escape, keeping your plants warmer. You’ll also find that a byproduct of using a grow light is the heat it kicks out; by using a grow tent this warmth will remain inside the tent and won’t be wasted.

The Lighthouse grow tents come with a clear window in the side. Whilst this doesn’t sound like the most groundbreaking addition to a grow tent, it is surprisingly functional: it allows you to check on your plants without opening the grow tent.

Nutrients

This is where we begin to feel the full benefits of our hydroponic system! You’re probably aware that plants need certain nutrients for healthy growth, and when planted in the garden, the plants are able to absorb some of these nutrients from the soil. How well they grow is dependent on how nutrient-rich your soil is.

General Hydroponics pH Down In a hydroponic system, we have what is known as a nutrient reservoir, which stores the water that is fed to the plants. The benefit of this is that we can mix soluble nutrients into the water, making it rich in nutrients in desirable quantities – water mixed with the soluble nutrients is called the nutrient solution, and this is what gets fed to your plants.

The important thing to consider when growing tomatoes is the pH level and the electrical conductivity. Tomatoes like the water to be slightly acidic, with a pH level of between 5.8 and 6.3. Most tap waters are around neutral (pH 7) and so will need to be adjusted by using a bottle of pH down, which can be gotten hold of easily and relatively inexpensively. I’d recommend purchasing a cheap pH level testing kit, which will allow you to test your tap water’s pH level. Then, it’s just a game of trial and error until you get the water to within the specified range.

Miracle Gro Tomato Plant FoodThe desired electrical conductivity (EC) is achieved by mixing the right minerals into the pH adjusted water (for those of you that are interested, tomatoes thrive with an EC of between 2.0 and 3.5 milliMhos). I tend not to worry about this too much – I won’t even test for it – as if you put the right nutrients into your system, this will take care of itself.

It is possible to get hold of a pack of general plant nutrients, which contain all the vital elements needed to grow. Whilst this will work reasonably well, if you have a system specifically for growing tomatoes it makes sense to have a tailored mix of nutrients that really give your tomatoes what they need. You can buy pre-mixed plant food specifically designed for tomatoes, and I’d highly recommend you pick a pack of this up (it will have all the right elements to take the EC to desirable levels).

Growing Medium

Rockwell for HydroponicsIf you grow outdoors, your growing medium is probably soil: this is generally because it’s found in abundance rather than because it’s the best compound for our plants to grow in.

In our hydroponic system we are able to change this growing medium to perfectly suit the needs of our tomatoes. I believe it’s worth considering what the commercial tomatoes growers are doing – they will have invested in researching the ideal growing medium, after all – and the overwhelming majority are using rockwool; who am I to disagree with that?

Rockwool is great as it holds water fantastically well (allowing your plants to take on more of the nutrient solution), whilst also holding high volumes of air; this supplies the roots of your plants with a good quantity of oxygen.

Rockwool is available in a range of sizes, allowing you to pick the best pack for your system.

How to Grow Tomatoes: The Growing Process

Right then, by now you should have your hydroponic system properly set up for optimal growth. Now we get to move on to the fun bit: the actual growing!

Seedlings

rockwool seedlingsEven if you are already growing tomatoes outside, I would be reluctant to introduce these plants into your new hydroponic system. Outdoors, plants will become contaminated by pests and disease. Introduce a contaminated plant and it can quickly spread throughout the whole system. I would always grow my tomatoes from seeds, thereby eliminating any possibility of infecting my system – this is a view point shared by most. The beauty of a hydroponic system is that you can control every aspect of the grow process, and this includes disease, so do everything in your power to avoid contamination: grow from seeds.

The best place to start is by placing them in individual rockwool cubes – you can pick up some small 1″ by 1″ cubes and these are perfect for our needs. Put the seeds into individual cubes, and if you have access to a growing nursery, put the cubes into this. Tomatoes germinate relatively quickly at 10-14 days; this means that they will only stay in the nursery for a short amount of time.

You should keep the rockwool cubes moist, using pH adjusted water (see above for how to achieve this). It doesn’t matter where they are kept, as long as it’s relatively warm. The moment the seedlings sprout, you should look to move them into a well-lit area though. Ideally, they will now be receiving light for at least 12 hours each day.

At this stage the plants are just about ready to be transported into the main system: wait until you either notice leaves or, protruding roots from the bottom of the rockwool cubes; whichever comes first. As soon as you see either, you can move the rockwool cubes across, and allow your tomatoes to join the main system! This takes around 10-14 days in most cases.

I would recommend that you put the plants at least 10 inches apart when placing them into your main system, as this will avoid overcrowding down the line.

Watering

3959587500_fc4f4ac6f0_mWhen you keep your plants in an indoor hydroponic system, they will only be fed when the system feeds them. Choosing the correct levels of water they receive each day is vital for a healthy plant.

As a general rule of thumb, a mature plant will need to be dripped with at least 4 liters of water each day. Obviously, juvenile plants will need less, and you should increase the amount of nutrient solution your plant receives as it grows.

Try to ensure the tomatoes’ growing medium remains moist (not wet) throughout the day. This is done by consistently watering your plants with small amounts of the nutrient solution, rather than drowning them with 4 liters in one go! This is all programmable and I would experiment with adjusting how regularly your plants are watered to achieve optimal results.

Pollination

tomato flowerAs your plants begin to grow, they will begin to develop flowers. It is absolutely essential that you remember to pollinate your plants, otherwise they will never grow fruit! Don’t neglect this step, whatever you do!

In nature, tomato plants are usually pollinated by the wind. Personally, I like to replicate this process by using a small fan to blow lightly onto the plants, spreading the pollen. Using this method has always worked in my experience, but there is no guarantee and you may feel more comfortable pollinating by hand.

Thankfully, pollination by hand is also a really simple process. As soon as you can see the stigma in your plant’s flowers, you can begin (the stigma is the bit in the middle of the flower that sticks out!). Get a small paintbrush and lightly touch the area around the stigma, called the stamen, which is where the pollen is. Then lightly touch the tip of the stigma to pollinate: yes, it really is that simple! If you really have no clue about the anatomy of a flower, lightly touching the tip of the paintbrush all around the flower should do the trick!

There is no guarantee that your plants will pollinate first time, so I would repeat this for several days to increase the likelihood that all of your plants will grow fruit.

Pruning

8517460786_ddbffdd8d5_mIt is essential to prune your plants. The majority of your fruit will grow from a small group of dominant stems; however, your plant will grow many other side-stems, most of which will never yield fruit. The problem is that the plant will provide these additional, useless stems with the nutrients it absorbs. This is unproductive, from our point of view, as it takes valuable nutrient resources away from the parts of the plants that yield fruit. Pruning the plant essentially means trimming away the useless parts.

Pruning your plant won’t harm it, and is highly recommended. If you’ve never pruned before, here are a few tips to help you out.

When your plant begins to flower, have a look at the lowest shoot the flowers are developing on. Any shoots below the flowers are known as “suckers” and these are the shoots that need to be pruned, as they are taking away vital resources. Simply snap off the suckers as close to the stem as possible, by breaking them off between your thumb and forefinger.

As your plant grows, there should be several prominent shoots which will bear fruit. To maximize the number of tomatoes produced, you should limit the plant to just these main shoots. Over time, these prominent shoots will begin to develop side-shoots. My advice is to break these off before they have chance to develop. They are unlikely to ever grow fruit.

Finally, try to remove any leaf or shoot that is starting to wilt. When the leaves turn yellow it means they are dying and are unlikely to benefit the plant in any way; despite this, the plant will keep providing it with nutrients, which are obviously wasted.

System Maintenance

5256931886_0e8d582fdb_zHydroponic systems are great: they take a lot of the manual aspects of gardening out of the equation, allowing you to sit back, relax and enjoy some tasty tomatoes! However, they aren’t miracle systems, and will need some maintenance on occasion.

As your plants absorb the nutrient solution the mineral levels will diminish. Whilst your plants will still be receiving nutrients, they may no longer be at the optimal levels and this can slow down growth.

Another problem is that the plants excrete a toxic salt over time, which remains in the growing medium, and, as the nutrient solution washes through it, might even begin to accumulate in the nutrient solution and the nutrient reservoir.

This is why it is essential that you add clean nutrient solution into your reservoir. I would aim to do this at least once a week (although if you have gone for the 8-pack system recommended earlier, you will need to do this far less frequently as it moderates itself). When you change the nutrient solution, it is recommended that you rinse out the reservoir with pH neutral water (ie, tap water) before adding the new nutrient solution back into the system ( for which you need to adjust the pH level and add the soluble nutrients to).

You should also leach your plants at this point. This involves picking up the plant and rinsing the growing medium clean of all that toxic salt that has built up around the roots, using pH neutral water again. This is something you will have to do weekly, and manually (even the 8-pack system has no way of leaching itself).

Harvesting

tomato ripening
So, we’ve done everything right, and it’s finally time for us to enjoy the fruits of all our hard work!

In general, tomatoes take around 60 to 90 days to grow and then ripen. In a hydroponic system, because you are providing the plant with the absolute best growing conditions, I would expect this to be sooner, and you should be enjoying your tomatoes within 60 days at the very most.

But when is a tomato ready for harvesting? When your fruit begins to turn red, you know it’s almost time. The best thing to do is to check the tomato in full: the fruit should be completely red, and consistent in color. If one side of your tomato is still green, give it some more time to ripen.

You should also gently squeeze your tomatoes to see if they are ripe (in the same way you would test them in a supermarket). A ripe tomato is somewhere in between “soft” and “firm”, so use this as your guide. In general, supermarket fruit is ripe, so if you are unsure what you should be looking for, head down to your local shop and test out their tomatoes to see what ripe feels like.

My preferred method of harvesting is to grab the tomato and twist it until it breaks away from the vine. It isn’t sophisticated, but it’s a technique that’s always served me well!

The Ultimate Growing Guide

So there you have it: my guide to growing tomatoes from scratch using a hydroponic system!

If you follow the instructions in this guide, you are sure to have wonderful, tasty tomatoes in abundance, and all year round!

So, enjoy them, and feel free to ask any questions by emailing me at shaun@hydroponicsgrower.org, and I’ll be happy to answer them!

7 thoughts on “The Mammoth Guide to Growing Hydroponic Tomatoes

  1. My name is Don & I am just getting started in DWC
    totes I have two with 22 gals of nutrients and 2 air pumps. I used the tomatoes formula 4-18-38 and keeping the PH at 6.0. The tips of the tomato plants
    have what it looks like burn edges. I have 2 florescent
    grow lights. I read that maybe the nutrients are right. Iike to start to correct but don’t know what to do first
    any help is appreciated Thanks Don
    l

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