How to Grow Tomatoes Indoors With LED Grow Lights; Steps to Improving Tomato Quality and Quantity of Harvest

Growing Tomatoes Indoors:

Growing tomatoes under LED grow lights has many advantages that encourage my year round participation in the activity.  I have been growing vegetables indoors and outdoors for over 15 years and in that amount of time, the produce I harvest is often better than what I could have purchased at the local market.  The yield I get is a product of my time and effort which always adds to the reward.  I know exactly how the plant was grown and this is very important to me.  Tomatoes are a staple in my indoor and outdoor gardens and throughout the rest of this post, I will review the basics of growing tomatoes indoors so that you can grow at home and enjoy the fruit of your harvest year round.

First and foremost, feel assured that you can grow tomatoes year round, indoors, under LED grow lights.  This is how I produce my tomatoes (often bush variety) and there are countless research articles that show great examples of successfully growing tomatoes under LED grow lights.

LED grow lights Support Indoor Tomato Grow:

Professor Cory Mitchell, professor of horticulture at Purdue University, reports that it is very expensive to ship tomatoes in from warmer climates and growing tomatoes under traditional HPS lights continues to be an expensive proposition as well.  Mitchell reports that growing tomatoes under light emitting diodes is a cost effective way to produce positive yield that could not have been accomplished with alternative grow lights.

According to the work that Mitchell completed at Purdue, LED grow lights are a good choice for indoor growing because they use up less energy and run cooler than traditional high pressure sodium grow lights.  During their grow experiments, they were able to get the same size yield with the same number of fruit that grew to equal sizes with high pressure sodium grow lights and LED tower grow lights.  The big difference between the two though was the cost of running the grow lights.  The LED tower grow lights ran efficiently using approximately 25 percent less energy than the traditional HPS lamps.

Another positive of using the LED grow lights to grow the tomatoes cited by Mitchell related to the light penetration.  According to Mitchell, since the LED grow lights run cooler, the plants can actually be placed a lot closer to the light which supports light penetration into the plant’s canopy and alongside the understory of the plant.  This factor enhances the plants ability to grow densely and produce more areas for fruiting.  LED efficiencies, PAR light recipe and light penetration are big reasons that Mitchell had success growing tomatoes.  These factors are also a big reason why you can have success growing tomatoes under LED grow lights at home too!

LEDs can Enhance Quality and Quantity of Yield:

If producing a great yield and cutting your overall energy usage is not enough incentive to encourage you to grow tomatoes under LED grow lights, maybe a better tasting yield that is more nutritious will do the trick.  I said earlier that I was happy to know what I was putting into my plants as they grow.  LED grow lights support my knowledge by allowing me to know the specific light wavelengths that I am utilizing to excite plant growth.  Although getting into the light spectrum and the photosynthetically active radiation range of light is a little beyond the scope of this particular post (click here for more information on light spectrum and PAR), it should be noted that LED grow lights are designed to emit the exact wavelength of light that plants need most to produce healthy yields.  LEDs can emit the right “light recipe” to optimize plant growth.  When plants receive the right light wavelengths that are research proven to optimize growth, quantity and quality of yield are improved.

One study conducted by Wageningen UR Greenhouse showed the tomato plants grown under LED grow lights produced fruit that contained twice as much vitamin C as the tomatoes that stemmed from plants that were not exposed to light from LEDs.  Another study conducted by Thomas Colquhoun out of the University of Florida showed that flavor to fruits and vegetables can be enhanced by LED grow light manipulation.  Research results reveal that flavor and nutrition of yield can be optimized when using LED grow lights.

What LED Light Will Support Tomato Growth:

Now that we have reviewed the “why” behind growing tomatoes under LED grow lights, lets delve a bit into the “how.” During my most recent grow, I utilized an LED grow light with an actual power draw of almost 400 watts.  This is sufficient for supporting healthy plant development during the vegetative and bloom stages.  The light incorporated 3 watt LEDs and was engineered to emit 8 bands of color spectrum when powered on.  The broad range of light spectra included blue and red wavelengths, as well as IR, UV, and white light.  I included this range of light spectra to closely align with the natural light that the tomato plants would have received had they been grown outdoors.  Making sure that the LED grow light you are utilizing covers a broad range of wavelengths, especially the red and blue light spectra that research shows is best for plant development, should be a priority.  Some LED grow lights are intentionally designed to support only specific plant growth stages.  Be aware and do a little homework on the grow lights specifications.  Make sure that the LED grow light is engineered to support the vegetative and flowering stages of a plant’s development and be sure that the light emitted includes both blue and red wavelengths.  Light within the photosynthetically active radiation zone is key.

Soil:

After the light is prepped and ready to go, you need to think about the other end.  The soil!  I do not recommend just digging up soil from outside.  It is too difficult to know exactly what you are getting and like I said, I like to know what I’m giving to my plants.  Using a potting soil mixed with another medium is a great way to pot your plants properly when growing indoors.  Check on the soil pH level.  A pH level of 7 is considered neutral and tomatoes grow best in neutral to near neutral soil.  The potting soil that I use contains organic matter, but you need to be careful not to over fertilize soil early on for fear of burning the plants out.  You do not want the soil to be too “hot.”  I always mix a hydroponic growing medium to the soil I use when growing tomatoes.  It is pH neutral and is made from natural coconut coir.  This helps to increase nutrient retention and also enhances soil aeration.  If your wondering, the potting soil I currently use is Happy Frog and the growing medium I mix in is CocoTek.  The ratio of soil to CocoTek that I use is 1:1  For more information on the basics of composting, click here.

Pot Choice:

The size of the pot that you choose to use may depend on your specific plans for the tomato plant.  If you plan on keeping the plant indoors the entire time, then starting with a larger pot is advisable.  If you plan on starting the plant indoors and then transplanting outdoors, then a smaller cell could be utilized.  Either way, fill about 3/4 of your pot with your soil-coir mix and then lightly moisten.  Follow seed insertion instructions for your specific variety of tomato plant, but in general, you will place the seed approximately 1/4 of an inch into the soil and then lightly cover the seed with your soil mix.  I will often plant more than one seed and then thin out later if necessary.  Once the plant reaches about 12 inches or more, you should consider transplanting into one gallon containers if you plan on keeping them inside for the entire grow process.

Temperature:

The ideal temperature zone for most plants is between 72 and 82 degrees.  Keep in mind that most tomatoes varieties are warm season plants but seedlings can be started indoors with temperatures even slightly below the optimal range I noted above.  Be sure to select an area of the home where you think you can effectively manage the ambient air temperature.  I do not recommend placing your plants near a vent in your home since temperature fluctuations are more extreme in these areas.  Air Conditioning blowing directly onto plants has a cruel way of ruining all of your hard work.  I have kept my room temperature 70 to 75 degrees and have had success.   For more information on soil mix and seed starting, click here.

Watering:

The soil and coir mixture will help to maintain a consistent moisture level throughout the grow process.  Using a moisture meter is one way to know the exact moisture level of your growing medium and to know when the soil needs more moisture, but I have always had success using the finger trick as well.  Making sure to stay away from the base of the plant and the root system, I press my finger into the soil to see if it is moist.  If the soil is dry to a depth of over 1 inch, then I give water.  If I am starting the plants in a small cell (3×3), I give about 10 – 15 ml of water at this point.  The soil and coir mix hold water well and will probably not need watering every single day.  There is no hard and fast rule to watering though, too many other factors, like the room’s temperature, will affect how often watering must take place.  Be sure to focus watering at the base of the plants near the rooting zone.

Support:

Taller growing varieties of tomato plants will need extra support to help them grow in a healthy manner.  In the outdoor garden, I have tried stakes, cages and even a trellis system.  These have all worked out well, but supporting tomato plants indoors can be a little trickier.  I tend to grow more compact varieties of tomato plants when I intend on keeping them indoors throughout their entire grow process.  The vine variety will likely require additional work for stabilization and additional pruning may be considered as well.  Look for compact or intermediate tomato varieties if you want to minimize the tomato jungle growth in your home.  Cherry and plum varieties are fan favorites around my house!

Harvest:

How soon should you expect to harvest?  Well, this depends on the specific variety of tomato plant that you have chosen.  In general though, tomatoes ripen in about 45 to 85 days after germination depending on the variety.  Your grow time will also be affected by the temperature at which you are growing your plants.  If your ambient room temperature is on the lower end of the acceptable range, then your plant will grow more slowly.  If your ambient room temperature is on the higher end of the acceptable range, be sure to water more often and expect to harvest a bit sooner!  For additional information on growing indoors with LED grow lights, check out our FYI at Grow Big or Grow Home.