Easily Grow Hydroponic Tomatoes Inside or Outside (without an Air Pump)

Growing tomatoes hydroponically is more simple than you may realize, and it creates vibrant and healthy plants. Whether you are growing in a greenhouse, under grow lights indoors, or outside under natural sun, this cheap and simple method will give great results without much hassle or expense.

Step 1: Watch the Video

The embedded video shows all the steps here in more detail and helps you to see what a simple process growing a hydroponic tomato can be.

Step 2: Pick Hydroponics Nutrients Well Suited to Tomatoes

There are many hydroponics mixes available. I use the MasterBlend mix from Morgan County Seeds, combined with some Epsom salt and calcium nitrate, but there are other blends that work which can be found online or at a hydroponics store. Look in particular for mixes tailored to growing tomatoes.

Step 3: Plant Tomato Seeds in Rock Wool

You can find rock wool grow plugs cheaply online or at a local hydroponics store. I recommend planting your seeds 1 per plug and then placing the cubes in a small pan (i use an aluminum baking tin). Add your hydroponic solution to the pan with the rock wool. Place the pan under grow lights or in direct sun.

Step 4: Purchase or Make a Net Cup

A net cup is a small cup that holds the plant suspended above the hydroponic growing solution, which allows roots to hand down into the nutrient solution. They can be purchased online, or, in a pinch you can design one out of a net cup.

Step 5: Locate a Small Plastic Container to Repurpose and Drill a Hole

Any container that can hold liquid, is reasonably opaque, and has a lid made of plastic should work. Coffee containers or baby formula containers work particularly well. Use the top of your net cup as a guide and trace a line around the outside of the top of the cup. You will want to drill a hole slightly smaller than that line so that the cup can be suspended. To prevent unintentionally cracking your lid, it is recommended that you step up your drill bit, starting with something much smaller than the hole you intend to drill and moving to larger bits until you eventually have a hole the size you need.

Step 6: Place Your Tomato Seedling Into the Net Cup

Roughly a month after starting the tomato seedling in rock wool, it should be ready to be transferred to your improvised container. You can place the rock wool directly into the net cup or, if your tomato stem is long enough to reach the bottom of the container while leaving some leaves above, you can peel away the rock wool and lower the tomato plant into the solution, allowing roots to sprout from the stem.

Step 7: Add Pebbles Around Your Plant

There is a lot of space in the net cup around your tomato plant. That space allows light to reach the hydroponic solutions below and can encourage algae growth in your nutrient mixture. Adding pebbles can prevent this. Pebbles also provide stability to you stem, helping to act similarly to soil in stabilizing your plant in place. I recommend clay pebbles called "hydration" available online or at hydroponic stores.

Step 8: Harden Off Your Tomato Plant (For Outdoor Plants Only)

After about a month of growing under your grow lights in the hydroponic container, it is time to take the plant outside and let it slowly adjust to the conditions outside. This video explains the process of hardening off your plants.

Step 9: Top Your Tomato Plant

While it may seem drastic you want to cut off the stem right in the middle. Make sure you have at least 4 true leaves below the spot where you make the cut. Topping your tomato in this way will help to thicken the stem, and make the plant bush out. Through continued pruning you can create a strong enough plant base that you do not have to stake or cage the hydroponic tomato.

Step 10: Transfer Your Plant to a Larger Growing Container

It is time to transplant to a larger growing container, and if growing outside, this container can be in full sun. Your roots need more room to grow. A 5 gallon container with a lid works well, you can use as little as a 3 gallon container with success. A 30 gallon trash can will give your roots lots of space and minimize the need for additional refilling of hydroponic nutrients. Make a hole in the lid for your net cup in the same way you did in step 5 for the smaller container. Pull your net cup, tomato plant, roots and all out of your initial container. Slide them into the bigger container. Fill the bigger container to a point where the bottom of the tomato roots are just touching the nutrients. Mark this point, and never refill your nutrients above this level.

Congratulations, you are now growing a tomato plant hydroponically.