How to grow lettuce indoors – Full Steps

In this article, we will talk about how to grow lettuce indoors and what factors you should consider achieving an abundant harvest.

Lettuce and tomato are plants that should be in every family garden. However, nowadays the spaces for gardens are becoming more limited. This is why we must look for options and techniques that allow us to plant indoors.

The question is how to grow lettuce indoors. Well, sowing in pots or indoors is not different from sowing in the open field. Both ways are ruled by the same principles. To have an excellent harvest a good seed and constant watering are the two pillars. Starting with the seed, we must pre-germinate them in trays for good root development and later transplant them into the final pots. Watering is essential during the whole cycle, especially during hot days. Harvest should be ready 30/35 days after the transplant.

Now hold on! Before we start to dive in deep on each factor we must learn about the lettuce briefly. By learning about the qualities and requirements of the plant, we will be able to understand better and prevent future problems.

Knowing the plant

Lettuce grows and develops better in regions where temperatures fluctuate between 18 and 21 ° C (65 to 70 ° F). The lettuce is very susceptible to frost. Regions where temperatures can go below 7/5 °C, could face some challenges in growing healthy lettuce.

As for light, lettuce is a plant that requires at least 12 hours of direct sunlight a day, but exposure of 14 to 16 hours is preferable. If we do not have this minimum amount of light, it is advisable to expose it to artificial light so it could grow well.

When will I harvest? On average, it takes 30 to 45 days for lettuce to mature after planting the seeds. This may vary slightly depending on the variety we decide to plant.

How to grow lettuce indoors?

Before you start planting, is important to choose the correct variety of lettuce. Since you will be growing it indoors you may have some space limitations. If you do not have a large space, it is advisable to choose mini lettuces, although varieties such as butter lettuce and loose-leaf lettuce are also excellent for growing in containers and indoors.

Below we detail the most used varieties.

  • Garden Babies
  • Merlot
  • Baby Oakleaf
  • Salad Bowl
  • Lollo Rosa

1 – Pre germination or direct sowing

The first step is to choose if we are going to do it directly or if we are pre-germinate and then transplant. Both methods have their advantages and disadvantages. We will recommend it whenever possible to pre-germinate.

Pre-germination is good for the plant since at the beginning the seed is fragile. Pregermination helps establish a dense root system, which will aid the development once transplanted.

If we choose to pre-germinate in trays, we must consider using a starter substrate. Although it is not something that affects us too much if we do it for family consumption.

We can use compost or a loose consistency substrate. We must place 1 seed per cubicle and water it gently.

After 10/15 days, depending on the environment and the variety, the seedling will be ready for transplantation.

It should be remembered that the pre-germinated tray must be finely watered every day.

2 – Transplant

For the transplant, we must consider the number of plants that we are going to have for each pot.

Each lettuce plant requires 4 to 6 inches (10 to 15 cm) of space and 8 inches (20 cm) of depth. Pots or containers should have drainage at the bottom to prevent water from flooding the pot. Make a hole 5 cm deep or as necessary so that the neck of the seedling is even with the soil. The process is quite simple, we recommend not transplanting more than 4 seedlings per pot, as these will compete for the resources available in the soil.

For the substrate, a mixture of 70% coconut fiber and 30% worm castings is recommended. This mixture is especially advised for growing on terraces or balconies because it lightens the weight of the pot. You can also simply grow with a “Universal Substrate” that we find anywhere, although if possible it is better to enrich it with a little earthworm humus (25%)

After the transplant is done, we should water the pot generously. The morning is the best hour to do the transplant, the seedling will suffer less.

How to grow lettuce indoors

3 – Cares you need to know on how to grow lettuce indoors

Lettuce is a very simple plant to take care of but not to the point that it could be left unattended for long periods. Especially when watering.


Lettuces are highly susceptible to water deficits. It is important to maintain good moisture soil during the entire crop development. If we see that the leaves begin to wither and dry, it is an indication that the humidity is not enough. It is advisable to water every day, preferably in the morning for better absorption.

If you don’t think watering is necessary because the soil appears to be still wet, dip your finger into the soil once or twice a day and water the lettuce if the soil feels dry. The soil should be moist but not puddled.

Good and Bad watering

As mentioned before, lettuce grows best at temperatures between 18 and 21 ° C (65 to 70 ° F). Don’t get it wrong, the plant will grow the same if the temperature is a few degrees above or below. Although you should know that if the temperature reaches extremes, the plant will stop its growth, and if the exposure is prolonged it can wilt and die.
The symptoms that the ambient temperature is very low is reflected in the growth, in this case, the plant will stop growing and frost injuries will occur, which will be seen in the form of wet patches on the leaves, as a result of the cells freezing.

The opposite happens with temperatures above the ideal, or at the extreme. When lettuce is exposed to temperatures greater than 30 ° C for long periods, we will notice that the plant grows quickly without the possibility of increasing the area of ​​the leaves, it will produce a long stem that when consumed will have a bitter taste.
If the weather is warm or cold enough outside, you can move the plants outside regularly to give them fresh air.

Place the plant near a sunny window or fluorescent grow light. Lettuce plants grow best in direct sunlight. Lettuce needs a minimum of 12 hours of sunlight a day, but exposure of 14 to 16 hours is preferable. If in your region the daylight doesn’t reach the minimum, consider buying a grow light.

If you’re using a grow light, turn it on for 14-16 hours instead of 12 hours.


Lettuce requires a lot of nitrogen to grow large and healthy. Nitrogen is the main nutrient responsible for the leaves’ growth. Our recommendation for this plant is to do it in two steps.

The first application must be base fertilization, this can be done when we proceed to transplant from the seed trays to the pots. We can use a nitrogen-based fertilizer, such as urea. The application is simple, when loading the pot with the soil we only do up to halfway, at this point we apply 20/30 g of urea and cover the other half again. The application should be made towards the edges of the pot, spreading the urea evenly.

The second application can be done 15/20 days after transplantation. We can do it by applying it in liquid or granular form. We recommend doing it in a liquid way with a nitrogen-based fertilizer, this application will only boost up the last half of the development.
When applied in liquid and by spraying, it will make the leaves absorb nitrogen faster, giving a healthy appearance.

Fertilization is not a crucial step for a good harvest. When planted in our houses this step can be skipped. Generally, the soil we used will still have many nutrients available.

Professionally, it is recommended to fertilize. During successive harvests the soil becomes poorer, reaching the point that the extracted nutrients must be replaced.

Weeds and Diseases

Weeds are common and must be removed from the pot. If we use some homemade substrate they may have a significant amount of weed seeds. It is advisable to carry out weekly pruning. Remember that other plants will be competing with our lettuce for nutrients if they are not removed.

Like any other plant, lettuce suffers from diseases. Being a plant whose edible part is close to the soil, we must take extra care to avoid the appearance of diseases.

If we talk about diseases we can write pages and pages about each type of fungus or bacteria. In this blog, we want to simplify and help you prevent them from appearing.

Always remember that all fungal and bacterial diseases need 3 elements to live. High humidity, high temperature, and oxygen. If we limit 1 or more elements we delay or avoid an excessive propagation of any disease.

Therefore, always remember that we must water during the morning, to avoid prolonged contact of the leaves with a humid environment such as the soil.

Avoid over-wetting the leaves, although it is pleasant to look at wet and apparently fresh leaves, the only thing we are doing is promoting the appearance of diseases.

4- Harvest

The harvest can be done from day 30/40 after transplanting. This can vary depending on the variety and our own taste.

Older leaves will have a slightly more intense flavor and the younger ones will be more tender.

There are three ways to harvest lettuce.

First option

The first option would be only to collect the leaves that we are going to consume. In this case, cut the outer leaves leaving the inner ones with the root in the pots, these will continue to grow and you can harvest them for several months. Cut 3-4 of the outer leaves at a time with garden scissors, allowing the rest of the plant to heal and regrow later.

Second option

Is the most common, if there are many diners we can harvest the entire plant, we suggest that the soil must be moist when harvesting to prevent the leaves from being damaged when pulled from the ground.

Third option

This would be to cut the entire plant without removing the root from the pot. If the entire plant is cut, it is convenient to leave about 5-7 cm of the stem to facilitate regrowth. After 2 weeks or so we should have new leaves ready to harvest.

Our recommendation is to harvest in the morning. During this time of the day, the plants are more hydrated and with less stress.

This will result in a longer life after harvest. Avoid harvesting in the afternoon or at midday. Plants are generally under stress during these hours due to the intensity of the sun.

How to grow lettuce indoors

5 – Storage

Lettuce can be refrigerated for 5 to 8 days after harvest. The best way to preserve the leaves once extracted is by cutting and cleaning them well with water plus removing the leaves that are damaged, these will only rot faster and affect the healthy leaves. After washing them, we must keep between kitchen paper in a closed tapper ware, the kitchen paper must be placed one at the base, one in the middle, and the last one above the last layer of lettuce.

It is not advisable to store them in a bag and without washing them since it exposes the healthy leaves to rotten ones, by storing them in a tapper ware we shield our harvest from damage.

6- Other tips on how to grow lettuce indoors

If we want to have a constant harvest, consider sowing seeds every 2 weeks, this will guarantee a continuous supply of lettuce.

If we choose to cut the leaves and leave the root in the pot to later harvest again, it is advisable to do it only 1 time. The second or third time you will not have the same results.

If we have a homemade substrate you will want to minimize the chances of having diseases or harmful insects, we can proceed to disinfect the substrate before planting.

For this purpose, we can use commercial products intended for disinfection, or we can proceed to do it ourselves. To do this, and taking into account that they are pots, we can boil water and pour it into our pot. We repeat this process 3 times in 6/8 hour intervals. This should reduce the harmful outsiders in a good manner.

Wrap Up – How to grow lettuce indoors

Planting in containers and pots is not very difficult. On the contrary, it is quite simple. We always recommend pre-germinating the seeds in trays by doing this way we achieve a strong plant from the beginning. Let’s not forget to water constantly every day, it is very important, especially for lettuce. As for fertilization, it is not necessary if we grow it for self-consumption, although is always welcome if the soil is poor in nutrients. We always harvest during the morning when the humidity of the soil help pulls out the root with ease.