Growing Romaine Lettuce Indoors

One of the biggest perks of starting your own garden is always having fresh produce on hand. Growing outdoors is great, but comes with the weather and seasonal constraints that can hamper your ability to grow. That’s why many gardeners are moving their gardens inside. Today, we’ll look at growing romaine lettuce indoors, and how to properly care for it. By the end, you’ll be able to grow beautiful romaine lettuce, and always have fresh leaves for your salads!

Why Romaine Lettuce?

Romaine lettuce (also called cos lettuce) is a variety of lettuce that is quite tolerant to both heat and cold. This makes it perfect for growing indoors, as it will thrive in the temperature swings a home typically experiences.

Romaine lettuce is also very easy to grow and doesn’t need too much light, at least compared to other vegetables. This makes it an excellent candidate for indoor gardens where sunlight is often at a premium. It also has a delicious, crunchy bite which makes it very popular in all manner of salads.

Location and Lighting

If you want your Romaine lettuce plant to thrive indoors it all starts with choosing a good location. Sunlight is often your first concern, and you’ll want a location that gets at least 6 hours of bright, indirect light per day. Less than this and you’re likely to see stunted growth.

You also want to make sure you have enough space for your chosen container. One of the perks of romaine lettuce is that it can grow in containers as small as 6” in diameter. You can always go bigger through, and the larger container you use will correlate to a larger crop come harvest time.

Choosing a Container and Soil

The best containers for lettuce are those that are shallow but wide. Lettuce tends to have short but wide, spreading roots, so a container that plays to that strength is best. You can use deeper containers, but fill the bottom few inches with rocks to help promote drainage.

Speaking of drainage, make sure that the container you choose has drainage holes or other similar features. You don’t want to leave your plant sitting in soggy soil as this can lead to root rot and kill your plant.

For soil, choose a high-quality potting soil or vegetable-specific soil. This will give your plant the nutrients it needs to grow. If you’re starting from a seed, you can use special seed-starter mixes until it’s ready to be transplanted.

Planting Your Lettuce

When starting your lettuce you have three general options, seeds, seedlings, or using a cutting. Let’s briefly go over all three.

The easiest option is to simply use a seedling from a hardware store or nursery. These can often be directly planted into your container of choice and cared for from there. This is often easier than starting with seeds and gets you harvestable lettuce more quickly. Unfortunately, this option may not always be available depending on where you live and the current season.

Starting with seeds is another good option. You can start with a seed tray, or simply sow them right into your container of choice. You’ll ultimately want to give about 4” of space between seeds, but you can always prune back to this distance once your plant sprouts. After sowing, keep the soil moist and warm until the plants begin to sprout, then move to standard care routines.

You can learn more about some common mistakes when growing from seeds from our article.

Lastly, you can use a cutting from store-bought lettuce. Simply take the bottom inch or so of the lettuce head and place it into a cup of water. This will begin to sprout new leaves that can be harvested. Lettuce grown in this way will typically be smaller than traditionally grown lettuce but is a good way to reuse old lettuce scraps.

Watering and Feeding

You’ll want to keep the soil moist but not drenched. Check the top inch of the soil, and water once it is dry to the touch. Typically, this will be about once per week, but may be more if it is unusually warm. The best advice for watering is to get into the habit of checking the soil daily.

During very warm and sunny periods you can also mist daily. This will help keep your plant’s moisture levels up without risking overwatering. It can also help if you’re having humidity issues.

You can fertilize during the summer every other month with a water-soluble fertilizer diluted to half strength. You can also use a slow-release fertilizer that can often feed for an entire growing season. Lettuce growth will typically slow during the winter months and therefore you likely won’t need to fertilize as often or at all.

Harvesting Romaine Lettuce

Usually, Romaine lettuce takes around 60-80 days after you plant the seeds to mature. You want to start harvesting your lettuce once it has at least 5-6 leaves that are about 4” in length. You have two good ways to harvest:

First, you can simply pick a few leaves. Take a few of the outer, mature leaves and gently pull them from the plant. This will give you a small harvest, but leave the rest of the plant to continue to grow. You can do this fairly often, and doing so is actually good for the plant as it will encourage fuller growth.

You can also harvest the entire plant by cutting about 1” above the soil line with a set of gardening shears. After this, the plant will continue to grow, and it will be a few weeks before you’ll be able to harvest again. This will give you more lettuce than picking individual leaves but will prevent you from harvesting again for some time.

A quick note, romaine lettuce will begin to bolt later on in the season or if it stays too warm for too long. This will ruin the flavor, and you won’t be able to harvest after this occurs. You can pinch off the flower buds to extend harvest time a little bit.

Growing Romaine Lettuce Indoors

Growing romaine lettuce indoors is a great way to have a year-round supply of this delicious vegetable. Romaine lettuce is a relatively easy vegetable to grow and is overall quite hardy. Give it a shot, and let us know how it goes!

Growing Romaine Lettuce Indoors FAQ