How to Grow Tomatoes Indoors with Lights | Can Tomatoes Grow Indoors

How to Grow Tomatoes Indoors with Lights – There are definite rewards to learning how to grow tomatoes indoors with lights.

Will tomatoes grow indoors? Yes, they certainly will!

And in this article, I’ll be covering how to grow all kinds of tomatoes indoors. After all, the growing ‘rules’ are pretty much the same for each, including:

How to grow cherry tomatoes indoors

How to grow hybrid tomatoes indoors

How to grow heirloom tomatoes indoors


An almost year-round supply of homegrown tomatoes is ideal! Homegrown tomatoes always taste so much better than shop-bought.

But there is a ‘however‘…

And that ‘however‘ goes like this:

Unless you invest in dwarf-growing tomato plants, tomato plants are not dwarf-like in proportion. They grow pretty big. Depending on the type – determinate or indeterminate – tomato plants can grow anything between four feet in height and upwards of ten feet in height. Plus, when planted in containers, tomato plants do best in large containers. 


The requirement for additional ‘size’ does pose a problem for the indoor tomato grower. 

There are two ways to get around this problem:

First, you grow tomatoes indoors at the start of the tomato growing season. Then, you plant your tomatoes outdoors – either in the garden or in large-sized containers.

The indoor growing can be in your home or it can be in a greenhouse.

Second, you have a decent-sized area in your home that you can utilize as a dedicated growing area. This way you can hang overhead LED lights and grow many tomato plants. 


In this article, I’m going to cover the first option: Grow indoors at the start of the growing season. Then transfer your tomatoes outdoors when the temperatures are high enough and there’s plenty of sunlight. 



How to grow tomatoes indoors with lights

Part of the reason that homegrown tomatoes taste so much better than store-bought tomatoes is that most hothouse growers select fast-growing tomatoes.

No harm in that.

But what many professional growers then do in order to maximize yield, and thus, maximize profit is to force the tomatoes to grow more quickly. Then, the tomatoes are often harvested a little too soon, so they are not given an opportunity to develop. Hence, you get tomatoes that have little flavor. Look good, yes. But no flavor.




How to grow your own tomatoes indoors – choosing the right tomato

You need to select the right tomato – the right seed – to have optimal results with respect to your indoor tomato growing pursuits.

Tomatoes are categorized in two ways: either they are determinate or they are indeterminate. 

For a full explanation read: What’s the difference between determinate and indeterminate tomatoes.

For a brief explanation, determinate tomatoes are less vigorous-growing tomato plants. They produce a single set of fruit. Once the fruit has set they quit growing.

Indeterminate tomato varieties are more vine-like. They are, generally so, vigorous growing. They continually grow and they continually blossom.


Which type do you think is best for indoor tomato growing purposes?


It’s the indeterminate tomatoes that are best.

Funny that – I would have chosen the smaller, determinate type if I didn’t know any better.


There is a huge array of tomato varieties available to us these days. In order to select the variety that you want, you should consider the following:

  • How long will it take the tomato plant to produce fruit that is harvestable?
  • What do you wish to utilize your tomatoes for? You may wish to eat them straight off the bush. Use them in sandwiches or in fresh salads. Use them for sauces and/or salsa. Freeze them.


Otherwise, you also need to consider the indoor location for growing your tomatoes. You probably know that already. But keep in mind that indoor-tomato growing is pretty straightforward; what’s not so straightforward is creating ideal growing conditions.

When you’re reliant on LED grow lights for tomatoes to produce the necessary illumination, there are certain temperature ranges that should be adhered to. In fact, this is no different from growing tomatoes in a greenhouse or outdoors in the garden – there are certain temperature ranges that are ideal. 

Throughout the germination stage, when growing indoors under LED lighting, it’s best to keep the temperature somewhere between 70-75 degrees F (21-24 C). Throughout the growth stage, you’ll want to maintain ambient air temperature between 75 and 80 degrees F (24-26.7 C).

For optimal fruit production, you’ll want to provide your tomato plants with at least eight to nine hours illumination each day. For this reason, if you can, position your tomatoes as close to a south- or west-facing window as you can. Obviously, the LED lighting will be available should your plants not be getting quite enough illumination. 




How to grow tomatoes indoors with lights step by step – timing

When should you begin this entire process? Keep in mind that here we’re discussing growing tomatoes indoors until they reach ‘transplantable’ proportions. Then, when large enough, it will be time to transplant outdoors. 

Really, timing is down to where you are in the world. Where you are in the U.S. Where you are in the U.K. Where you are wherever.

The key is never to plant tomatoes outside until the threat of frost has passed. That is unless you’re going to provide your tomatoes with some frost protection. 

So it’s best to work with this in your area. Find out the date of the likely final springtime frost where you are. Then plan to transplant your tomatoes outdoors around two weeks after this date has come and gone. 

The general rule is to start tomato seedlings around six to eight weeks prior to the likely date of the final springtime frost. 

In the U.S., in USDA plant hardiness zones 10 and 9, start your tomato seeds from early to mid January. 

In zone 8, start tomato seeds indoors during early February.

Zone 7? Go for mid February.

In zone 6, start seeds in late February.

For zone 5, you’re looking at a seed starting date in early March.

And for zones 1 through 4, mid to late March is good timing to start tomato seeds. 


How about in the U.K.? When to plant tomato seeds in the U.K.?

Again, depends on where you reside.

But let’s say the typical last springtime frost date where you are in the U.K. was at the end of May then you would sow your tomato seeds (indoors, of course) from mid- to end of March.



How to grow your own tomatoes indoors with lights – seed starter soil mix

(Incidentally, this post contains links to products. Please make the assumption that at least some of the links may result in earning commissions. Thank you.)

The initial step to how to grow tomatoes indoors with LED lights is the preparation of a good blend of starter soil for the tomato seedlings.

Well, that’s what many tomato growers will do – blend their own starter soils. 

For me though, I prefer to invest in shop-bought rather than create my own potting soils. 

I like to use something like Espoma SS16 16-Quart Organic Seed Starter:


best tomato seed starter soil mix
Espoma SS16 16-Quart Organic Seed Starter 



Espoma SS8 8-Quart Organic Seed Starter consists of peat humus, sphagnum peat moss, and perlite. Plus, there’s a ‘thing’ called Myco-tone in it which is mycorrhiza fungi. These fungi promote root growth, increase the uptake of water and nutrients, and essentially, this all works together to generate larger plants that have more abundant flowers.

And because of the inclusion of peat this seed starter mix is on the acidic side – ideal for tomatoes.

You’ll need a seed tray for your seeds. There are many different types available. I like to use organic biodegradable seed trays: 

best organic biodegradable seed trays for tomatoes

Seed Starter Peat Pots Kit – Biodegradable and Organic


Add your seed potting mix to your starter trays. Moisten the potting mix just prior to planting the tomato seeds. Plain tap water is fine for this.




How to grow tomatoes in pots indoors – planting your seeds

Plant your tomato seeds around 1/4 inch deep. You can add numerous seedlings to each starter tray cell. I like to add around two to three seeds to each cell, spacing them out as much as possible. 

To keep the potting mix nicely moist, cover your seed tray/s over with something like plastic wrap. 

Your seeds will germinate best if the ambient air temperature is 70-75 degrees F (21-24 C) or thereabouts.

Most of your seeds will sprout over the coming five to 14 days. As soon as you see the seeds coming through, remove the plastic wrap topping. 

Your grow lights (and we’ll get to what type of lighting and lighting system is best in just a moment) should be approximately two to four inches above the seedlings.

Once the seedlings start to pop through the potting mix, turn your grow lights on and keep them on for 12-16 hours daily. This encourages healthy vegetative growth. More on this a little later.

After the seedlings reach 1 1/2 inches in height, transplant them into four-inch pots. At this point, you’ll want to add a single seedling to each four-inch pot. Hence, choose the strongest-looking seedlings and discard the remainder.


best peat pots for tomato seedlings - How to Grow Tomatoes Indoors with Lights

Organic, Biodegradable, Eco-Friendly 4″ Pots for Tomato Seedlings



 LED grow lights for tomatoes – the benefits

I don’t want to make this article into a book. There’s no requirement here to go into all the pros and all the cons of choosing LED lights over other types of lighting systems. And there’s no need to provide reviews about which LED lights are best and why.

This is about growing tomatoes. It’s not about why you should choose one lighting system over another.

Suffice it to say that LED (which stands for light-emitting diodes) lights have been available to us for a long while. They are much more energy efficient for indoor growing than other lighting systems such as HPS lighting, HID lighting, and even fluorescent lighting. 

They – LED lights – offer the right color spectrum of light. Thus, using LED lights will help to ensure that your tomato plants will be healthy, vigorous, and provide you with optimal fruit yield.

There are downsides to using LED lights in comparison to other lighting systems. However, for the part-time home tomato growing enthusiast, the pros of using LED lighting outweigh the cons. 




Best LED Lights For Indoor Tomato Growing

There are many great LED lights for indoor tomato growing available. However, for the part-time grower – the grower that perhaps wishes to grow indoors to get their tomato seedlings to the transplanting stage – it’s probably pertinent not to overspend on some really fancy lighting system.

This is why I myself prefer to stick with something pretty simplistic, that looks and acts more like a desk lamp than a true, professional growing light setup.

The Vogek LED Plant Growing Light is my personal favorite for this purpose.


indoor growing lights for plants - How to Grow Tomatoes Indoors with Lights

Leoter LED Plant Grow Light



The Leoter LED Plant Grow Light features 80 LEDs (36 red, 16 blue, and 28 full spectrum). It also comes with an auto ON/OFF Timer so that it automatically turns on/off every day in accordance with your settings. The Leoter has 10 dimmable modes to suit varied stages of plant growth. It has 10 levels of light intensity and 3 spectral modes to meet different stages of plant-growing needs.


You’d expect this product to be really expensive, given all of its capabilities and functions. Actually, it’s really affordable




Growing tomatoes indoors with LED lights – lighting and feeding

When plants are grown under artificial lighting they do need a lot more of that artificial lighting than they would do if they were outdoors in sunlight. Tomatoes require six to eight hours of sunshine to perform optimally. To grow optimally indoors with little to no natural light they’ll need a lot more than six to eight hours of artificial light. 


Tomato plants bear flowers and fruit. As such they require a certain period of darkness to ‘encourage’ the flowers and fruit. In this case, that period of darkness is eight hours. Not all plants need eight hours of darkness. Tomato plants do.

Start using your grow light as soon as your seedlings begin to sprout. Keep the light two to four inches above the height of the seedlings. 

Your light can be turned on for 16 hours each day. Turn on just after sunrise. Turn off 16 hours later. This light timing generally emulates springtime outdoor lighting conditions. 


As for fertilizer; I like to add a fertilizer early on to my tomato seedlings. And, of course, I keep on adding throughout the entire lifecycle of my plants.

A good seedling starter fertilizer for tomatoes is Dr. Earth Organic 5. 


best fertilizer for tomato seedlings - How to Grow Tomatoes Indoors with Lights
 Dr. Earth Organic 5 Tomato Fertilizer


Dr. Earth Fertilizer’s N-P-K ratio is 4-6-2. That may be a little low in terms of N (nitrogen) for seedlings. You want to provide plenty of N at the start of your plants’ lifecycle. Nevertheless, it does provide good results. And P (phosphorus) is nicely high). Ideal for healthy root growth.


By the time I’ve transplanted my tomatoes outdoors (usually to large-sized containers as I don’t always have access to garden space), when the plants are just starting to show flower, I’ll change fertilizer. I want something that is higher in K (potassium) and lower in N. Why so? Because potassium is what’s required for optimal fruit growth. 

So, with this in mind, I like Espoma Tomato-Tone Organic Fertilizer. This has an N-P-K ratio of 3-4-6. Ideal for tomatoes that are approaching fruit production stage of the lifecycle!



best fertilizer for tomato fruit production - How to Grow Tomatoes Indoors with Lights
Espoma Tomato-Tone Organic Fertilizer



Espoma Tomato-Tone Fertilizer also contains calcium. Calcium is an all-important ingredient in deterring tomato blossom-end rot which is a commonplace problem faced by tomato growers. 

Read: How to stop tomato blossom-end rot


For tomato seedling growth, the ambient air temperature will ideally be between 72 and 80 degrees F (22-27 C) in day time and 65-70 degrees F (18-21) during the night.

Once your tomato seedlings are around eight inches in height, you’ll want to transplant the seedlings into larger containers as they will be on the verge of outgrowing their 4-inch pot homes. Five-gallon (19-liter) sized containers are fine. 

Some folks prefer far larger-sized containers than five gallons. Some people insist on a 20-gallon pot for each single tomato plant.

Sure, that’s great for the plant. Tomatoes like plenty of space for the root system. But for many folks filling, say, ten pots that are each of 20-gallon capacity with potting soil is not an option.

This is the point in time, needless to say, that unless you are growing in a sizeable dedicated growing space in your home or you’re growing in a greenhouse, you’ll need to move your tomatoes outdoors. 

The plants start to grow beyond the proportions that a small indoor growing area can handle. What’s more, a bunch of five-gallon-sized pots is going to consume a lot of floor space.





Once the flowers are developed and once they start to open, daily pollination should become routine. 

For optimal pollination, humidity should be between 65 and 70 percent. Not that this is within your control if your tomatoes are now growing outside.

For the greenhouse tomato producer, the timing of optimal pollination is also important. Tomato producers typically perform the activity between 11.30 am and 12.30 pm (around noon). For the professional tomato grower, manual pollination does not take place earlier or later than this because fruit production suffers.

All of this info is more relevant to the indoor tomato grower that has plenty of available growing space or to the greenhouse grower. Nevertheless, even for tomatoes grown outdoors, it can prove to be beneficial to utilize the same techniques for pollination.

The following video provides graphic illustration as to how to manually pollinate tomato plant flowers.

Enjoy the accompanying music!



 How to hand-pollinate tomatoes




Final Tomato-Growing Tips

To finalize, just a quick word about suckers. 

Tomato suckers grow from the plant’s leaf axils – the part where the branch joins the main stem. It’s prudent to pinch out the suckers as soon as you see them. 


Suckers, as the name suggests, ‘suck’ nutrients and water from the plant. That’s nutrients and water which could, instead, be used by the fruit. 

No need to prune suckers off. Rather, just carefully ‘nip’ them out with your fingers. 


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