Growing Tomatoes with LED Lights (Complete Guide)

We all know that nothing tastes or smells better than a ripe and juicy home-grown tomato. And those of us who are avid gardeners always ensure that we grow plenty of tomatoes during the summer months because these plants need both warmth and plenty of sunshine.

But what if you knew that you could grow tomatoes all year round? Well, you can by growing them indoors under LED grow lights during the winter months. Now, growing tomatoes indoors is not as simple as planting some outdoors into a well-prepared garden bed.

There are certain conditions that you have to provide for indoor-grown tomatoes, and that’s what we’re going to discuss in this article. So, here’s the complete guide to growing tomatoes indoors using LED lights.

Find the Right Spot to Grow your Tomatoes

The first thing you have to remember is tomatoes need warmth as well as light. Therefore, you need to find a spot in your home that will be warm even during the coldest winter day. This is because tomatoes don’t handle variations in temperature very well, especially if it gets really cold.

If you have a south-facing window in your home that is situated in a room that is constantly kept warm, then this would be ideal. The tomato plants will get a little natural light coming in from the window, which will boost the light that they get from the LEDs.

The other thing you should remember is that tomato plants can get really large, especially if you’re growing indeterminate varieties. You need to ensure that the light has enough room to hang above the plant and can be adjusted as the plant gets larger and larger.

For this reason alone, it might be worth only growing determinate tomatoes indoors. These won’t get quite as tall and may well be easier to manage. They’ll also require minimal pruning and can be successfully grown in a tomato cage.

The only downside to growing determinate tomatoes is that your crop is going to ripen at the same time. However, this problem can be overcome by starting successive plants one month after each other if you have the space.

growing tomatoes under full spectrum led lights

Choosing the Right LED Light for your Tomatoes

As tomatoes are fruiting plants, you want to select a full spectrum LED light. These types of grow lights emit different kinds of light that are essential for the effective flowering and fruiting of your tomato plants. Here’s an explanation of the different light spectrums:

  • Blue or white lights are useful for the germination of seeds and to promote strong leaf and stem growth.
  • Warm white light will encourage your plant to flower as it’s similar to warm sunlight.
  • Red light combined with blue and white light will stimulate the production of both green growth and fruit.
  • Infrared light will encourage your plant to provide a better and higher yield.

As you can see from this explanation, for fruiting plants such as tomatoes, you’re going to need all the different color spectrums in order to grow your plants successfully indoors.

While you’re germinating your seeds and then while the plants start to grow leaves, you want to ensure that you use the blue or white lights.

Once your plant has put on plenty of green growth, switch on the warm white light to encourage it to start flowering. To encourage fruiting, use the red light and then switch on the infrared light to increase fruit production once the tomatoes start to grow.

At this stage, when your plant is in full fruit mode, you can use all the lights concurrently in order to promote both good growth and plenty of fruiting.

Control the Intensity of the Light during Each Stage

When considering the right type of growth light to purchase, it’s important to select one that has the ability to adjust the intensity of the light. You also want to ensure that the light is height adjustable as you’ll most likely need to raise it numerous times as your plant grows.

Here are the four major stages of tomato plant growth and what light intensity is required at each stage:

  • For seed germination, the light intensity should be around 20 to 40 percent.
  • During seedling growth, you want to set the light to intensity of around 40 to 60 percent.
  • While the plant is putting on lots of green growth, it will need a light intensity of around 60 to 90 percent.
  • Finally, at the flowering stage, the light intensity should be set to 90 to 100 percent.

Ensure Good Seed Germination

Tomatoes seeds are more likely to germinate reliably at a temperature of around 77 degrees Fahrenheit (25 degrees Celsius). The LED light should give off a little heat to help with this, especially if you have it fairly close to the level of the seeds.

Ideally, you want to have the height of the light around 4 to 6 inches (10 to 15 cm) above the level of the soil.

You can also aid germination by creating a more humid environment. You can do this simply by placing a cloche or plastic bag over the pot until you start to see the seedlings emerge. If you’re going to do this, make sure to remove the cloche and raise the height of the LED light as soon as the first seedling emerges because you don’t want to cook your new plants.

Remember that Tomato Plants need a period of Darkness too

It makes sense that tomato plants need both a period of strong light and a period of darkness if we want to simulate the ideal growing conditions for them. For this reason, you want to select an LED growth light that comes complete with a timer.

This will give your plants a regular day and night cycle, just as they would experience if they were growing out in the garden during summer. If your plants receive continuous light without a period of darkness, they will become exhausted, and this can cause damage to your plants that is irreparable.

Ideally, your plants should be receiving good strong light for around 12 to 16 hours every day. This will ensure that the plant is being exposed to the correct daily cycles for effective photosynthesis and good growth.

Choose a Good Potting Mix

When growing tomatoes indoors in a pot, choosing a high-quality potting mix is vitally important. The mix needs to be free-draining and contain lots of organic matter, such as compost.

You also want to ensure that you have a good-sized pot that has drainage holes. For mature tomato plants, you want a pot that is at least 12 inches (30 cm) deep with about the same or slightly larger diameter.

Ideally, you’ll want to start your seeds in a smaller pot or seedling tray and then move the seedling into a larger pot as it grows. Once the plant is around 6 inches (15 cm) tall, you can plant it in the large pot that it will continue to grow in.

Consider using a Heat Mat

As you are aware, tomatoes not only need plenty of light to flower and fruit, but they also need warmth. If your home is cold in winter or the room where you’re growing your tomatoes tends to have frequent fluctuations in temperature, then you should consider using a heat mat.

Heat mats are placed under your plants to provide a constant source of warmth for the soil and the roots. As long as the soil is warm enough and your plants are getting plenty of light, they should thrive and provide masses of fruits.

Give your Tomato Plants the Right Amount of Water

Watering indoor tomato plants is vastly different from watering those that are grown out in the garden. Although tomato plants are rather thirsty, you do want to avoid letting them sit in waterlogged soils for extended periods of time.

The best thing to do for this is to check the moisture level in the soil on a daily basis. You want to keep the soil nice and moist but definitely not waterlogged. One of the easiest ways to test the moisture level in the soil is to poke your finger into it up to the first knuckle.

If you feel that the soil is dry, then it’s time to water. However, if the soil still feels quite damp, then avoid watering and check again the following day. You might also want to invest in a soil moisture meter to make this process easier.

Don’t Forget to Feed your Tomato Plants

The best solution for feeding indoor-grown tomato plants is to use liquid tomato feed around once every week or 10 days. You can adjust this schedule if your plant is putting on too much green growth and not producing any fruit. Instead, try feeding them only once a fortnight.

Hand Pollinate your Plants

Because there are no insects or wind when you’re growing your tomato plants indoors, you have to hand pollinate them to get maximum yields. This can be as simple as gently shaking the stems on a daily basis or using a soft paintbrush and brushing gently all over the flowers.

Having an oscillating fan near your tomato plants will help with this but make sure that the fan is not directly pointing at the plants themselves.