Celtuce (Stem Lettuce)

Direct sow a quarter to a half inch deep as soon as the soil is workable, or set out transplants carrying four to six true leaves. Seed germinates best at soil temperatures around 55 to 65 degrees. Do not hold this sowing back waiting for settled warm weather. Celtuce is day length sensitive, and long photoperiods push it into bolting, which in this crop means flowering by stem elongation. Successive plantings made in late spring run into lengthening days and bolt bitter and inedible before the stem ever sizes up, so the earliest sowing is the one that actually makes a crop.

Side-dress a nitrogen fertilizer such as 21-0-0 at a quarter cup per 10 feet of row - at thinning if you direct sowed, or four weeks after setting out transplants. Place it to the side of the plants rather than over them, and water it in. Repeat the same feed on a late summer sowing. The stalk is a store of what the leaves make, so early leaf growth is what thickens the stem later - a plant that never builds a canopy never builds a stem. Placing the fertilizer beside the row and irrigating it in keeps salt off the foliage and carries it down to the shallow feeder roots that take up nearly all of this plant's water and nutrients.

Once the seedlings have a few true leaves, thin them to roughly 8 inches apart in the row. Do not throw the thinnings away - young celtuce leaves are tender and good in salad. Keep taking the odd young outer leaf as the plant grows, but stop once the leaves toughen, and never strip the plant. The swollen stalk is the crop and it is built from what the leaves photosynthesize, so the plant needs both room to thicken and its leaf canopy left intact. The leaves are only worth eating while small - as they mature they grow bitter and become inedible, so the salad window and the stem window are two different harvests.

Make a second sowing in late summer, counting back from your first hard freeze so the stalk gets its full days to maturity in cooling weather - check your variety, since celtuce runs anywhere from about 50 to 85 days. In mild-winter regions this same crop can be sown in fall or winter. Celtuce is a cool season crop that wants a mean temperature of about 50 to 60 degrees, and the shortening days of late summer and autumn keep it vegetative so the stem thickens instead of running to flower. Midsummer supplies neither condition, which is why the fall sowing is usually the better crop.

Give 1 to 2 inches of water per week, by drip where you can. The goal is steady soil moisture - do not let the bed cycle between soaked and bone dry, and pay closest attention in the weeks the stem is filling. Fluctuating soil moisture is what makes the stalk tough and stringy and brings on tipburn, and drought stress is one of the reliable triggers that tips a day-length-sensitive plant over into bolting. Celtuce roots are shallow and horizontal, so the top few inches drying out is a real check on growth, not a cosmetic one.

Twice weekly, check both the upper and lower leaf surfaces of plants through the planting, beginning along the outside rows where aphids show up first. Hold off spraying until numbers pass roughly 20 aphids per plant. Above that, azadirachtin or insecticidal soap are the organically acceptable materials - soap only kills what it physically wets, so cover the leaf undersides. Green peach aphid does more harm as a virus vector than as a feeder, carrying alfalfa mosaic and beet western yellows into the planting, and infestations start in clusters at the field edge rather than spreading evenly. Catching them on the outside rows is the difference between a spot treatment and a lost crop.

Cut the plant when the central stalk stands 12 to 18 inches long, taking it down into the leafy part of the plant. Peel the stem before eating - the soft, translucent green central core is the edible part. If the plant begins to bolt, harvest it at once rather than waiting for more size. Peeling is not optional: the outer edges of the stalk carry a bitter, milky sap, and only the core inside is mild. The whole plant grows more bitter as it matures, so the tender window is narrow and the crop is finished once flowering takes over.

Through cool, wet weather, check leaf undersides for white fluffy growth, usually under pale yellow angular spots on the upper surface. Keep water off the foliage - run drip or a soaker at the base of the plants, let the bed dry between irrigations, and if you must water overhead do it early in the morning so the leaves dry quickly. Hold the spacing open for airflow, and pull and destroy infected plants and end-of-season debris rather than composting them. Resistant cultivars are available and are the easiest win where this disease is chronic. Downy mildew needs cool, moist conditions and foliage that stays wet, so drying the canopy is the control that does the most work in a garden. Fungicides only help preventively or very early in disease development, not as a rescue once leaves are infected - which is why prevention and prompt removal are the plan. Infected debris left in the bed is the spore source that starts the disease again next season.