🌿 Onion

Use a fertile, well-drained or sandy potting soil with good aeration and moderate water-holding capacity. Incorporate well-decomposed compost or organic matter for structure and nutrient supply, but avoid fresh manure (which can encourage sluggish growth and disease). Prevent soil waterlogging: onions perform poorly in heavy clay; use raised beds or add gravel or organic matter to improve drainage. The best soil pH is slightly acidic to neutral (around 6.0-7.0).

Onions (Allium cepa) can be grown from seed, graft or plant. From seed (recommended for optimum bulb size and storage): - Sow indoors 8 to 12 weeks before the last expected frost (earlier in cooler climates), or sow directly as soon as the soil can be worked in spring. - Sow seeds at a depth of 0.5-1 cm (1/4-1/2 in.) in fine potting soil; maintain regular humidity. Germination generally takes 7-14 days at a temperature of around 18-24°C (65-75°F). - Grow seedlings in daylight; avoid letting them dry out. Harden off 7-10 days before planting. - Transplant outdoors in early spring when plants are pencil-thick and the risk of frost is low to moderate (onions tolerate light frosts). Plant the white stem just below the soil surface; do not bury the growing point. Direct sowing in the open ground: - Sow thinly in rows; cover lightly. Thin out seedlings in stages to final spacing. From seedlings (small dormant bulbs): - Plant bulbs in early spring as soon as soil is workable (or in autumn in mild-winter climates where overwintering can be relied on). - Plant the bulbs 2-3 cm deep, tip up; cover them so that the tip is just above the surface of the soil. Spacing: - Space plants 10-15 cm apart for medium/large bulbs (tighter spacing for smaller bulbs), with 25-30 cm between rows. Location and planting care: - Use full sun and well-drained, fertile soil rich in organic matter; avoid fresh manure. - Keep soil constantly moist during establishment and early growth; avoid waterlogging. - Keep beds free of weeds (onions are not very competitive). Stop watering abundantly when the bulbs reach maturity and the tops begin to fall off, for better drying. Note on timing: - Choose cultivars adapted to day length (short, medium or long day) and sow early enough to allow strong vegetative growth before swelling is triggered by increasing day length.

Fertilization should be based on a soil analysis; onions have shallow roots and respond best to fertile soil containing sufficient phosphorus and potassium before planting. Incorporate well-decomposed compost and/or a balanced pre-planting fertilizer, then concentrate on nitrogen at first to stimulate leaf growth (bulb size depends on number and size of leaves). Side-dress with a readily available nitrogen source, in small, repeated applications (usually every 2-3 weeks) from establishment to bulb initiation/when bulbs start to swell. Stop applying nitrogen once bulbs start to swell, to avoid thick necks, delayed ripening and poor storage quality. Avoid heavy fertilization at the end of the season, and avoid fresh manure.

Apply a light, weed-free mulch over the onions once the seedlings/transplants are established and the soil has warmed up. Use clean straw, shredded leaves or finished compost in a thin layer (about 2-5 cm) to conserve moisture and suppress weeds on their shallow roots. Keep mulch away from the plant neck and developing bulbs to reduce moisture entrapment and rot, and avoid thick, soggy mulches that can slow soil warming. Reduce or remove mulch at the end of the season to help bulbs dry and harden, especially in wet weather. In cold regions where onions have overwintered, add thicker winter mulch after the ground has begun to freeze and remove it in early spring.

Onion bulbs (Allium cepa) are traditionally used as a food remedy and are a source of sulfur-containing compounds (e.g. thiosulfines) and flavonoids (notably quercetin) with antioxidant and anti-inflammatory activity. Experimental and clinical nutrition studies associate high onion/allium consumption with cardiometabolic support (e.g., modest improvements in blood pressure, lipid oxidation and platelet aggregation) and a potential benefit for glycemic control, although effects vary according to preparation and dose. Onions also provide prebiotic fructans, which can promote intestinal microbiota and bowel function. Crushed raw onion juice and purees have been used in folk medicine for minor skin irritations and as an antimicrobial, but this does not replace medical treatment and may irritate the skin in some people.