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Bitter Lettuce: Why Your Lettuce Is Bitter And How To Fix It

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Have you ever wondered, why is my lettuce bitter?

Bitter tasting lettuce is most often caused by hot weather. But there are other reasons lettuce gets bitter including maturity, bolting, and poor growing conditions.

I love growing lettuce and fresh homegrown lettuce really does taste so much better then what is available in most grocery stores.

But one of the most common problems when growing lettuce is that you get frustrated with how bitter it can taste.

Then you start wondering why the lettuce you grow tastes bitter and worse then what you’ve been buying.

Why Your Lettuce Is Bitter text overlaid on a close up photo of green leaf lettuce.

Often this is simply caused because you aren’t understanding the growing needs of lettuce. Lettuce grown in the right conditions is sweet and something you want to eat lots of.

Through a lot of trial and error, we’ve learned how to grow lettuce all summer and it doesn’t taste bitter, quite the opposite it’s sweet, crunchy, and full of flavor.

Common Causes Of Bitter Lettuce

Red leaf lettuce growing in the garden with green lettuc in the background.
Try growing lettuce varieties that tolerate heat.

Heat

The most common cause of bitter lettuce is the summer heat. Lettuce is a cool-season vegetable and when temperatures start to get to warm the plant will start to mature faster and bolt.

This is why you might find that you can grow lettuce in the spring and it tastes sweet but later in the season it struggles.

Lettuce grows the best between 60 and 70 F (15.5 and 21.1 C). When temperatures rise above this it can slow the plants growth.

This causes you to have older leaves to harvest that just won’t taste as sweet as younger leaves. It also stresses the plants and stressed plants don’t taste good.

When we harvest lettuce for our markets early in the morning the leaves taste sweet and crips, but if you were to pick the same lettuce plants during the heat of the day they can have a bitter aftertaste.

Bolting

Not long after lettuce plants grow to their mature size they will start to bolt. This means that they send up a flower stock so that the plant can produce seeds.

Bolting can also be caused by heat, lack of water, and anything else that causes stress to the plant.

Lack of water

Not watering enough can also cause bitter lettuce. Like most greens, lettuce needs a lot of water to keep healthy and sweet tasting.

Make sure to provide 1 inch (2.54 cm) of water a week if you haven’t had enough rainfall. If you are dealing with very hot conditions or a drought then increase your watering to 2 inches (5.08 cm) per week.

Poor soil

Fast-growing lettuce simply tastes better. One cause of lettuce that’s slow to grow is not having fertile soil.

This can happen from tilling your garden for years without adding nutrients back to the soil.

Why Is My Lettuce Bitter And What Can I Do To Stop It?

Harvest Early In The Morning

Red and green lettuce growing in the summer garden covered with water drops after being watered.
Red and green lettuce growing in the summer garden.

In the early spring when the weather is cool you can harvest lettuce just about any time of day. However, once the warm weather arrives it’s best to pick lettuce early in the morning.

Once the temperatures start to rise the leaves will start tasting bitter no matter what type of lettuce you are growing.

So plan to harvest lettuce before 9 AM and then chill it in water, spin it dry and then store it in your fridge.

Harvest Younger Leaves

Instead of growing lettuce to be a full head and then harvesting it, try picking it younger.

You can start picking the outer leaves just a few weeks after transplanting into your garden. Continue to harvest the outer leaves every week while you let the smaller ones in the center to keep growing.

This actually helps the plants to grow faster and produce more food then letting it just grow a single head. But the younger leaves taste sweeter then more mature leaves do.

Provide Shade

If you are growing lettuce through the summer it’s very important to provide shade.

The easiest way is to plant in the natural shade cast by trees or buildings. The best location will be one that gets morning sun and afternoon shade.

If your yard doesn’t have any shade then try using shade cloth. This simple cloth can be hung over your plants to block some of the sunlight and heat.

Water Often And Mulch

Lettuce plants have shallow roots so they are very prone to stress when they don’t get enough water.

Watering often can help but remember to still water deeply as this will encourage the roots to go further down into the soil. Then mulch around the plants to help the soil to stay evenly moist.

Fertilize

To help lettuce plants grow quickly you need to have rich, fertile soil.

The best way to start building soil health is to add good quality compost to your garden every year. This can be from your own compost pile or a local garden center.

If adding compost isn’t an option for you right now then you can fertilize your plants with an organic liquid fertilizer like fish emulsion or liquid seaweed.

Grow The Right Varieties

The type of lettuce you grow also has a lot to do with how it will taste.

Some varieties have been developed to have more heat tolerance than others. These types are slower to bolt and will grow better in hot areas.

Common Bibb lettuce, often called Butter or Boston lettuce doesn’t handle high temperatures well. These types will bolt quickly when hot weather arrives.

Whereas buttercrunch, romaine, red sails, and ruby tolerate high temperatures much better and are slow to bolt.

While the main cause of bitter lettuce is hot temperatures that naturally happen in the summer, don’t forget to also make sure you are harvesting early in the morning and providing enough water and nutrients to the plants so that they can grow quickly.

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