Spinach

Direct-sow seed half an inch deep and 1 to 3 inches apart, about 2 to 3 weeks before your average last frost, once soil has warmed to 40F. Emergence takes 7 to 10 days. Make sequential sowings about 2 weeks apart to stretch the window. Spinach bolts on lengthening days and heat, so the crop is a race against the solstice and every week of cool weather you capture early is leaf you get to eat. Germination is best at 55-65F and soil above 80F actively suppresses it, so a late sowing fails at both ends.

Four weeks after transplanting, or at thinning, band about a quarter cup of a nitrogen fertilizer such as 21-0-0 per 10 feet of row along the side of the plants rather than over them, and irrigate it into the soil. Spinach is a heavy feeder harvested for its leaves rather than a fruit, so nitrogen is the yield - it goes straight into leaf size and tenderness. Placing it to the side and watering it in keeps fertilizer salt off the crowns while carrying the nitrogen down to the roots.

Thin the stand once plants have 3 to 4 true leaves, to roughly 3 inches apart in rows about 12 inches apart. Lift the thinnings with some root still attached and set them into gaps rather than composting them — they transplant successfully if some roots are maintained, and they are also good eating. Repeat after the fall sowing. By 3 to 4 true leaves the seedlings are already competing with each other for the nitrogen and water that make a big tender leaf, and a plant pulled at this size still carries enough root to restart somewhere else instead of being wasted.

Starting mid-spring, turn leaves over weekly and look for neat rows of small white oblong eggs under 1mm on the undersides. Pick and destroy those leaves, along with any showing tan blotchy mines, and check again 7 to 10 days later. The larva feeds between the two leaf surfaces, so once it is inside, control gets much harder and the practical moment to act is before the eggs hatch. With 3 to 4 generations a season, the eggs you crush in spring are the flies you do not fight in midsummer.

In cool wet spells, watch for dull yellow patches on the upper leaf with purplish-gray fuzzy growth on the underside beneath them. Pull and bag infected plants rather than composting them, and keep spinach off that ground for 2 to 3 years. Irrigate early in the day, or by drip, so foliage dries before nightfall. The pathogen runs hardest at 59-70F with long periods of leaf wetness, and it makes its spores overnight to be carried off on the next day's air currents - so wet leaves at dusk are what it needs. It also leaves oospores that survive a few years in the soil, which is why the ground itself becomes the source of the next infection.

Cover the bed with floating row cover or insect netting right after thinning, held up on hoops so the fabric cannot abrade the leaves, and seal the edges to the soil. Do not cover a bed where spinach, chard, or beets grew last season - rotate that planting to new ground instead. Spinach leafminer overwinters as pupae in the soil and the adults emerge around mid-May to lay eggs, so cover works only as an exclusion fence put up before the flies are flying. Over ground that grew a host crop, the same cover traps the emerging flies inside with your spinach.

Begin once plants have enough leaf to be worth picking, any time before the flower stalk forms. Either strip the older outer leaves and let the young ones keep growing, or shear the whole plant to within 2 inches of the soil, leaving the growing point undamaged so it regrows for further cuts. Take one final full harvest as soon as a flower stalk appears. The crown keeps pushing new leaves for as long as you do not cut it out, which is what makes spinach a cut-and-come-again crop rather than a single picking. Once the plant bolts the leaves go thin and bitter, so the rising flower stalk is the signal to strip the plant rather than nurse it.

Sow again about 6 to 8 weeks before your average first frost, around mid-August in much of the country, for harvest from late September onward. For an overwintered stand, finish sowing early enough that plants are well rooted before the ground turns cold. A fall crop matures into cooling weather and shortening days instead of racing them, so it simply never bolts, and spinach is a hardy annual that stands through heavy frost. The same sowing that feeds you in October is the stand that overwinters and explodes in early spring.

As hard cold arrives, cover the fall stand with a heavy frost blanket, adding a second layer when lows in the teens are forecast. Lift the cover to inspect or harvest only once the day has climbed into the 40s, and re-cover with enough daylight left for the bed to warm again before the overnight cold. Spinach itself already takes heavy frost, so the blanket is buying root-zone warmth and blocking desiccating wind rather than saving the leaves, and settled snow on top only adds insulation. Growth nearly stops through the darkest weeks, then the surviving crowns restart and crop from February onward.