Cut one plant at the base and look at the center. If the core is stretching upward into a cone or a stalk, and the leaves along it are smaller, thicker, and more pointed, the plant has started to bolt, and bitterness comes with it. If the plant is still flat and leafy but tastes harsh, look at the last two weeks instead: a hot spell or a bed that dried out can turn leaves bitter before any stalk shows. Outer leaves tend to taste stronger than the young leaves in the middle, so taste from the center before deciding the whole planting is gone.
Heat is the most common cause. Lettuce grows best when average daily temperatures sit between 60 and 70°F. Above that, growth slows, the leaves may turn bitter, and the seedstalk forms and stretches quickly. Butterhead types such as Bibb can turn bitter once temperatures climb above 75°F. Seedstalk formation is driven by a combination of long days, warm temperatures, and plant age, so a spring planting that tasted fine for weeks can turn in a few days once early-summer heat arrives.
Water stress comes next. Lettuce has shallow roots, and soil that swings between soaked and dry stresses the plant; that stress tends to show up as bitter flavor and earlier bolting. Extension guides call a steady, even moisture supply one of the keys to a good cr. Age is the third factor. A loose-leaf planting you have picked for five or six weeks is closer to flowering than a young one, even in mild weather. Crowded plants competing for the same water tend to turn sooner as well.
If a stalk is already rising, harvest the whole planting now. The leaves do not turn sweet again on a bolting plant, and they get more bitter each day. Wash the leaves and refrigerate them for a day or two before eating; Illinois Extension notes this can soften some of the bitterness. The young inner leaves are usually the mildest, and bitter leaves are often more pleasant cooked, wilted, or mixed with milder greens. Pull the bolted plants afterward so the space can go to a .
Next season, sow small amounts every two to three weeks starting about 4 weeks before your last spring frost, so a young planting is coming on, and stop as early-summer heat arrives. Slow-bolting types such as Buttercrunch and Red Sails tend to hold longer than most. Give late-spring sowings afternoon shade from taller crops or shade cloth, and to keep the soil evenly moist. Then sow again about 7 weeks before your first fall frost. Lettuce that matures into cooling fall weather is often the sweetest of the year.
- SlugIrregular holes in low-growing plants overnight, with silver slime trails left behind on leaves and soil.
- Fruit CrackingTomatoes crack at the stem end or shoulder, cabbage heads split, and carrots split lengthwise — usually after heavy rain follows dry weather.
- Early BlightDark spots with concentric rings on lower leaves that yellow and drop, working up the plant.
- Southern BlightWhite cottony mycelium and small round sclerotia at the stem base, with rapid plant collapse in warm, moist soil.
- Crown RotThe base of the plant turns brown and soft at the soil line, and the plant collapses — caused by wet-soil pathogens attacking the crown.
- Why did my broccoli skip making a head and go straight to flowers?Broccoli bolts when it experiences heat or stress during head formation — once it starts flowering, the head is unsalvageable, but timing adjustments can prevent it next season.
- What does drought stress actually look like, and how do I know when to water versus when something else is wrong?Drought stress progresses from midday wilting to all-day wilting, leaf curl, and eventually aborted fruit and flowers — the key is catching it before the plant has been dry long enough to abort reproductive structures.
- How can I extend my growing season in fall?Row cover fabric, cold frames, and switching to cold-hardy crops are the three most reliable tools for extending production 4–6 weeks past your first fall frost.
- What are the white or tan papery patches appearing on my leaves during a heat wave?White or tan dry patches on the upper surface of sun-exposed leaves are heat scorch — the leaf tissue has been killed by a combination of excessive temperature and direct solar radiation.