Nothing is quite as satisfying as harvesting your own fresh lettuce for salads. If you have limited garden space or can only grow indoors, lettuce is one of the best choices to grow in pots for beginners and seasoned gardeners. With four to six lettuce plants, you can harvest a big salad every week or so during the peak growing season.
Full-sized lettuce can easily grow in a pot as small as 1 gallon (3.8 L) at least 6 inches (15 cm) deep. Lettuce grows best in full sun but can quickly bolt if exposed to extreme hot or dry conditions, so it’s important to move pots into a partially shaded area during heat waves in the peak of summer. If grown indoors, lettuce can thrive under a fluorescent light or an LED grow light, kept on at least 10 hours a day. As lettuce is a light to moderate feeder, use a balanced fertilizer or one with higher nitrogen.
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What Size Pot Do I Need to Grow Lettuce?
Lettuce is a very forgiving vegetable, and doesn’t need a large pot to grow to its full size. As a general rule, whether you’re growing head lettuce or leaf lettuce, pots should be at least 6 inches (15 cm) deep. You can grow them in smaller pots, but the leaves will be smaller. One of my favorite varieties, a romaine-type lettuce called Parris Island Cos, forms cute little lettuce heads if I grow them in solo cups, but will grow lush, full-sized leaves if planted in a 1-gallon (3.8-L) container. 1 gallon is more than enough for one lettuce plant.
If you are using a large pot and planting more than one lettuce plant, space head lettuce about 6 to 8 inches (15-20 cm) apart. Leaf lettuce can be planted a little closer together. If you are growing lettuce solely for baby greens, 2-4 inches (5-10 cm) is adequate spacing.
As always, with any container being used for growing vegetable, ensure it has enough drainage holes at the bottom, and fill it with a rich potting mix. In the case of lettuce, you can even use pure compost, but if making your own mix, compost mixed with some perlite or vermiculite is ideal.
“Whether you’re growing leaf lettuce or head lettuce, you can pick the outer, lower leaves of your lettuce plants, while leaving the smaller central leaves to continue growing.”
Light Requirements of Lettuce
With lettuce, the more sun it gets, the faster it will grow. However, lettuce has a tendency to easily bolt (produce a flower stalk) if exposed to very hot or dry conditions. Bolting is not good for lettuce because it signals the end of the plant’s life cycle as it tries to produce seeds for the next generation. As a result, the leaves become smaller and often taste bitter. You will know lettuce is starting to bolt because it will start quickly growing taller while having smaller and smaller leaves.
Because of this, lettuce does grow best in spring and fall. But since you’re growing lettuce in containers, you can temporarily move lettuce to partial shade or full shade during heat waves without harming your lettuce, and keep it growing longer. You can also position your lettuce in a way that it can get the warm morning sun yet be shaded during midday to avoid the scorching heat. In the summer, I like putting my lettuce pots on the north side of my potted fig and citrus trees so they can get shaded at noon but still get sun through the rest of the day.
Best Time to Plant Lettuce
If you’re growing lettuce outdoors, you can either start lettuce indoors and transplant, or direct sow. Lettuce is one of those few vegetables that can be sowed up to a month before your last frost, but it will germinate and grow slowly until the weather warms up or you cover it with some kind of plastic sheeting, cold frame, or cloche.
You can continue succession sowing more batches of lettuce throughout the year, but in the peak of summer you may notice your lettuce is bolting more frequently.
For a fall planting, you can sow your seeds around 8-12 weeks before your last frost.
Growing Lettuce in Pots Indoors
If you want to get started growing veggies indoors, lettuce is perhaps the easiest to grow and gives you the best bang for your buck. If you have a south-facing window, balcony, or sun room, you might not even need artificial lighting for your lettuce, but if you do notice they are getting leggy or their leaves look thin and weak, you may need to supplement with grow lights.
Growing Lettuce Indoors Under Lights
Lettuce does not need very strong light to grow. Flowering and fruiting crops generally have much higher light requirements. You can successfully grow lettuce under fluorescent lights (T4, T5, or CFL), but it’s important to keep the light as close to the top of your lettuce plants without touching the leaves in order to maximize the amount of light they get. You can also use full-spectrum LED grow lights. I like to use SANSI lights since they’re energy efficient and you can buy 36W bulbs for around $40, which can provide light for a 2×2 or possibly a 3×3 group of lettuce plants.
For lettuce, use a light cycle of at least 10 hours a day, up to 18 hours.
How to Fertilize Lettuce in Pots
Lettuce is a light to moderate feeder, and primarily needs nitrogen to grow. If you use new potting mix, you might not even need to fertilize your lettuce in pots during the season. However, if you want to push your lettuce to grow faster, you can give your lettuce weekly feedings of a well-balanced, all-purpose liquid fertilizer.
For organic options, the king of nitrogen fertilizers is blood meal. It provides the highest source of natural nitrogen, although it has few other nutrients (essentially just some minerals). Another good fertilizer to use is fish emulsion, which is a great all-around fertilizer, but unfortunately has a strong fishy smell if you apply it regularly. Still one of my favorites.
For plant-based fertilizers, alfalfa meal is a low-nitrogen fertilizer that will slowly break down and feed your lettuce. You can also give your lettuce a small boost by applying used coffee grounds as well. Coffee grounds have a modest 2-0.33-0.28 NPK, but the nitrogen is in a form that is instantly available to your lettuce. And as a by-product, it’s basically free fertilizer. Don’t worry about used coffee grounds acidifying your soil – much of the acid is leached out when you brew your coffee, and you would need to add huge amounts of it to your garden in order to significantly change the pH of your soil.
Harvesting Lettuce in Pots
When it’s time to harvest, I always recommend using the “cut-and-come-again” method of harvesting lettuce and other leafy greens such as kale and spinach. Whether you’re growing leaf lettuce or head lettuce, you can pick the outer, lower leaves of your lettuce plants, while leaving the smaller central leaves to continue growing. This way you don’t have to start over again by sowing new seeds; you can just come back a week or so later and have another set of full-sized leaves to pick.