Germination temperature
About 18-27 °C (65-80 °F); extension trials use 18-21 °C (65-70 °F) at room temperature or 21-27 °C (70-80 °F) on heat mats.
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Artichoke seed germinates easily, but a young plant only forms edible buds after a period of cold. This guide covers sowing, giving seedlings the chilling they need for a first-year crop, and why seed-grown Green Globe plants are not all alike.
About 18-27 °C (65-80 °F); extension trials use 18-21 °C (65-70 °F) at room temperature or 21-27 °C (70-80 °F) on heat mats.
About 2 cm (3/4 in), one seed per module or small pot.
About 10 days at 18-21 °C (65-70 °F).
No light needed to germinate; bright light as soon as seedlings appear.
Not needed to germinate. The cold that matters is for the seedling: about 250-500 hours below 10 °C (50 °F) before buds form.
Transplants. Raise seedlings in pots for 6-8 weeks, then plant out with 4-6 true leaves.
Sow more seed than you need. Seed-raised artichokes vary, and Connecticut trials grew about 20% extra seedlings so the weakest could be discarded at transplanting.
Not needed. The seed coat does not block water uptake.
Not needed for germination. As an optional way to start vernalization early, extension growers soak the seed for 2 days and then keep it moist in the refrigerator at 2-4 °C (36-40 °F) for 4 weeks, moving each seed to a pot once its root is 6-19 mm (1/4-3/4 in) long.
Optional. A 2-day soak in room-temperature water is part of the extension method above; for ordinary sowing, seed germinates without it.
Keep the seed at 18-27 °C (65-80 °F). Germination rates of 50-90% are normal, depending on the cultivar.
About 2 cm (3/4 in) deep, one seed per cell or pot to avoid disturbing the roots later. In Florida, 128-cell trays gave sturdier seedlings than smaller cells.
A free-draining seed compost. In the field artichokes prefer deep, fertile, well-drained soil around pH 6.5.
Keep the compost evenly moist but not wet.
Seed does not need light to germinate. Seedlings need full light at once; after germination grow them at about 24 °C (75 °F) by day and 18 °C (65 °F) at night, avoiding temperatures above 27 °C (80 °F).
About 10 days at 18-21 °C (65-70 °F); slower in cool rooms.
Plant out 6-8 weeks after germination, when plants have 4-6 true leaves. Harden them off for a few days and set them shallowly: planting deep can damage the growing point at the leaf bases. For an annual crop, space about 60 cm (2 ft) apart in rows 1.2 m (4 ft) apart; perennial plants need 75-90 cm (30-35 in) or more.
Young plants form buds only after enough cold: roughly 250-500 hours below 10 °C (50 °F), with Green Globe types at the upper end, about 500 hours. Cool nights after planting out usually supply this. Heat above about 27-29 °C (80-85 °F) soon afterwards can reverse it (devernalization), so mulch to keep roots cool.
Green Globe from seed is open-pollinated and variable. In a Connecticut trial, some plants grew about 60 cm (2 ft) taller than the rest and gave nine marketable buds each, while others stayed stunted; 28% of Green Globe plants were still barren in autumn. Keep the best plants and propagate them by offsets if you grow artichoke as a perennial.
Cause: not enough hours below 10 °C (50 °F), or heat that devernalized the plant. Fix: start seed so transplants meet cool weather, mulch roots, or grow the plant on for a second season. In warm-winter Florida research, 20 ppm gibberellic acid sprayed 43 and 64 days after transplanting replaced the cold and induced buds; untreated plants stayed vegetative.
Cause: heat. Temperatures above about 30 °C (86 °F) reduce tenderness and make buds open fast. Fix: time the crop so buds form in the cool season and harvest promptly.
Cause: moisture stress on sunny, warm, windy days. Fix: water about 25-50 mm (1-2 in) a week and keep a thick organic mulch.
Cause: both are common artichoke pests. Fix: check under leaves and inside young buds, wash off or treat aphids early, and protect transplants from slugs.
Cause: natural variation in seed-grown plants. Fix: discard off-type plants and keep offsets only from plants with good buds.
Artichoke is a Mediterranean cool-season plant. In subtropical climates it is grown as an annual from autumn to spring, avoiding the hot, wet summer. In India this means sowing so plants go out at the start of the cool season in the northern plains or in the hills, where winter nights give the chilling hours naturally.
Artichokes are large, hungry plants. Mature plants reach about 1 m (3 ft) across and 1.2-1.5 m (4-5 ft) tall, and need regular water and nitrogen; a side-dressing of calcium nitrate is a common extension recommendation.
Cut the main bud while it is tight, before the lower bracts begin to separate, with 5-7.5 cm (2-3 in) of stem. Side buds follow. Buds reach marketable size about 30-35 days after they first appear; left uncut they open into purple thistle flowers.
Where winters are mild (USDA zone 7 and warmer), plants can be kept for several years: the RHS advises removing flower stems in the first summer after planting and expecting the main harvest in the second summer, with up to 12 buds per mature plant.
Start Green Globe artichoke seed in time for the cool season and select the best plants for buds.
Yes, if the young plants get enough cold: roughly 250-500 hours below 10 °C (50 °F), about 500 hours for Green Globe. Plants that miss this, or are overheated soon after, stay leafy and usually bud in their second season.
Green Globe from seed is open-pollinated, so plants vary in height, vigour, spines and bud quality. Grow extra seedlings, discard weak or off-type plants, and propagate the best ones from offsets.
It needs a cool season. It suits the hills and the winter season of the northern plains, where nights are cold enough to vernalize young plants. In hot, humid lowlands buds may not form or turn tough quickly.