Swiss Chard

Direct sow once the soil hits 40F, about 2-3 weeks before your last frost

Sow seed directly in the garden 2-3 weeks before your average last frost date, as soon as soil reaches 40F. Plant seed 1/2 inch deep, about 1-2 inches apart, and expect 7-14 days to emerge; germination is fastest between 55F and 75F. Chard is slow to bolt and will hold through the hottest part of summer producing leaves, so unlike spinach one spring sowing usually carries the season - but in long, hot summers a second sowing is cheap insurance. Chard germinates in cool soil, but its value is that it is slow to bolt and keeps making leaves right through the heat that finishes spinach. Getting it up and growing early gives it a full established crown before summer.

1-2 inches a week, at the roots and never overhead at night

Give chard 1-2 inches of water a week, more in sandy soil or heat. Use drip or a wand at the base and avoid overhead irrigation. If you must water overhead, do it early enough that the leaves dry fully before dark - never in the evening. Two things ride on this. MSU Extension notes that plants which become drought-stressed are more likely to throw a flower stalk and stop leaf production. And extension leaf spot guidance calls for cultural practices that minimize periods of leaf wetness, including avoiding overhead irrigation - an evening sprinkler hands Cercospora the one condition it cannot manufacture for itself.

One midseason nitrogen sidedress, and only if the soil is poor

About 4 weeks after transplanting or once plants are established and picking has begun, sidedress a quarter cup of a nitrogen fertilizer such as 21-0-0 per 10 feet of row. Place it to the side of the plants, not against the stems, and water it in. On decent garden soil chard performs well with little or no fertilizer - if the leaves are large and dark green, skip it. Chard is a cut-and-come-again leaf crop, so every harvest removes nitrogen the plant needs to build the next flush. On poor soil that shortfall shows up as small pale leaves; on good soil there is nothing to fix.

⚠ Keep granular fertilizer off the leaves and crown - it will burn the tissue you are about to eat, and salt sitting in the crown rots it.

Thin to 6 inches once seedlings have 3-4 true leaves

When seedlings have 3-4 true leaves, thin them to 6 inches between plants, in rows 12 inches apart. The thinnings are good eating - use them as baby greens rather than composting them. Crowded chard holds moisture on its leaves for hours longer after rain or dew, and that leaf wetness is what Cercospora needs to infect; extension guidance lists increased plant spacing as a leaf spot control, so spacing is disease management, not just a yield tactic.

Check leaf undersides for leafminer eggs and crush them

Turn leaves over and look for eggs: small white oblong eggs under 1 mm, laid on their sides in neat little rows in groups of several. Rub them off with your thumb. Pick and destroy any leaf already showing a pale winding tunnel, and do not leave those leaves lying in the bed. Keep checking every 7-10 days - there are 3-4 generations a season, with flushes roughly in late spring, midsummer, and late summer. The egg is the only stage you can reach. Once the larva mines into the leaf it feeds between the upper and lower surfaces where nothing touches it, and each mined leaf is a leaf you were going to eat.

Cercospora leaf spot: protectant spray before the spots take hold

Watch for small tan to brown round spots with a distinct purple to red border, worst in warm humid spells. If your site has a history of it, start a protectant on a weekly interval before symptoms get severe rather than after. Products labeled for leaf spot on Swiss chard include Reynoutria sachalinensis extract (Regalia, PHI 0d) and thyme oil (Guarda, PHI 0h) among OMRI-listed options, and azoxystrobin (Quadris F, PHI 0d) as a conventional option. Cultural control does the heavy lifting: increase plant spacing, avoid overhead irrigation, pick off spotted leaves and remove them from the bed, and promptly incorporate plant debris after harvest. Cercospora is most damaging in warm humid weather and spreads by splash from spots already on the plant. Protectants only shield tissue that is still clean, which is why they must go on ahead of the disease rather than after it is established.

⚠ Pre-harvest intervals for Swiss chard per the New England Vegetable Management Guide: azoxystrobin (Quadris F) PHI 0d / REI 4h; Regalia PHI 0d; Guarda (thyme oil) PHI 0h. A 0-day PHI still means read and follow the label rate, and chard is picked continuously, so any product must be labeled for the crop you are eating that week. LABEL CAUTION: the source warns that applications of Quadris to leafy vegetables may cause phytotoxicity - proceed with caution regarding tank mixes and adjuvants. Be realistic about what this buys you: in the UMass 2021 organic trial the best treatments still left 31.3 and 32.5 percent leaf severity, and the Regalia + Badge X2 treatment was NOT significantly different from the untreated control on the final rating date. Sprays suppress this disease; they do not rescue a bed that is already covered.

Row cover against leafminer - but not over last year's chard ground

Cover the bed with row cover or insect netting before the leafminer flies are active in spring, sealing the edges to the soil. Critically, do not cover a bed where chard, beets, or spinach grew last year: the flies overwinter as pupae in that soil and a cover will simply trap them in with your crop. Rotate to fresh ground first, then cover. Beet and spinach leafminer flies lay their eggs on the leaf, and once the larva is inside the leaf it is protected from almost everything you could spray. Excluding the adult fly is the only control that reliably works, so the cover has to go on before she arrives.

Take the outer leaves young, and keep picking through the frosts

Start picking about 4 weeks in, once leaves are usable size, and take them young rather than letting them get big and coarse - younger leaves are the tastiest. Snap or cut the outer leaves at the base and leave the growing point and inner leaves alone, or cut the whole plant back to about 3 inches above the soil and let it regrow. Harvest early or late in the day. Keep going after light frosts - chard keeps growing until temperatures drop to the mid-20s, and a row cover or low tunnel stretches that further. The crown keeps making new leaves all season as long as it is intact, so picking outer leaves is harvesting the plant's output rather than the plant. Chard is a biennial grown as an annual, and MSU notes that if the plant is not damaged, harvesting can continue for up to two years.