Artichoke Cold Tolerance/Season
Artichokes need a long growing season, so northern and alpine gardeners should start them indoors under lights 8 weeks before the last frost date. Sow seeds ¼” (0.6 cm) deep, ¼” (0.6 cm) apart, and cover with ¼” (0.6 cm) of fine vermiculite or sifted potting soil.
[Artichokes have long taproots that do not like to be disturbed. Continue reading to learn how to handle the seeding and transplanting process]
|Growing Artichokes Thumbnail Sketch|
|Time to Harvest:
Optimum Growth Temp:
Optimal Soil pH:
Seeds or Seedlings:
| 85-100 days
Per Zone 7+, An Other
60-80° (15-27° C)
65-75° (18-24° C)
3-4’ (1-1.3 m) tall & wide
3-4’ (1-1.3 m) apart
How to Overwinter Artichokes
Artichoke seeds germinate in 10-20 days—earlier, when kept moist at 65-70° (18-24° C)….
Some artichoke varieties are frost hardy in zone 7 and above, and can tolerate winter low temperatures as low as 14° F (-10° C) if well-mulched.
Mulch and Cover Artichokes for Winter
“For zones 6 and 7: Cut plants back to roughly 12 inches tall. Mound organic mulch over the plants, then cover plants and mulch with an inverted bushel basket. Feel free to use compost as this first mulch layer. Add a layer of mulch (straw is great at this point) over and around the bushel basket. Drape a rainproof cover over the mound, taking care to anchor the edges.
“In spring, after the ground is no longer frozen and before growth begins, remove the winter covering. When new growth begins, fertilize plants again with Bonnie Herb & Vegetable Plant Food and add a 1-inch layer of compost or well-rotted manure around the plant.”
When to Harvest
Too Late for Eating
“The large buds on this artichoke plant are beginning to open and should have been harvested sooner for better flavor and tenderness. If buds are left to open on the plant, they can’t be eaten but they do make beautiful flowers in the garden.”
“To overwinter plants in cooler zones, cut them back to 8-10” (20-25 cm) in late October, then cover the stump with 10” (25cm) of straw or dead leaves to protect from frost. In the spring, uncover the stump to let it sprout.”
Choosing the right variety
“Artichokes are true perennials, even the ones sold as ‘New Annual Forms’ are, but the difference between named varieties is important if you live in most of the northern US. Forget about growing the so-called heirloom varieties (the violet ones such as Purple of Romania, Violetta Precoce or the green variety Green Globe) as they are all warm weather varieties, and they will not perform well in northern gardens. You will need to seek out varieties that can be raised from early sown seed, and that will form buds within the same year. I suggest seeking out IMPERIAL STAR ( available from Johnny’s Selected Seeds and from Seeds of Change) as well as the purple variety OPERA ( also from Johnny’s). NOTE: If you want to grow Cardoons, this is also the time to sow your seedlings, following the same methods….
ARTICHOKE ARE TAP-ROOTED, WHICH MEANS….
Even though Artichokes are challenging, they can be rewarding (as the best challenging tasks usually are). There are some helpful facts to know about, especially with the physiology of the plant. Artichokes are tap-rooted plants, meaning that they form very deep roots, even as seedlings. As most tap-rooted plants dislike any root disturbance, it makes sense to start seeds in very deep pots to reduce and twisting and turning in the pot.
A root that has turned and twisted in a seedling pot or flat can only spell disaster when you transplant it into the garden. These young plants will sulk and ultimately remain sickly in comparison to their well-rooted kin, who had their long, graceful roots carefully tucked into deep, rich soil with a minimum of distress. You must not try to touch or even straighten out roots, or you will stunt the growth for a few weeks. My solution for tap rooted plants is simple – use a seedling pot called RootTrainers – a 6-8 inch deep system that allows tap rooted seedlings extra room where roots can run deeper than typical seedling trays or pots. Do a Google search for them, Toilet paper rolls will not work well, as the long growing season will result in decay well before seedlings can be planted out, but you may want to try saving your plastic water bottles, and cut the tops off.
Seed must be sown into warm soil, and seed germinates best at 75º. I place my pots under lights, with a heating mat where they will stay for 3 weeks before being moved to the greenhouse, which will be warmer by mid February. Artichokes are warm weather growers, but they are not fans of hot weather. Temps in the 70’s are preferred, but the most important cultural note to follow is that seedlings will need a few weeks where they experience cold temps, called vernalization.
“When late March arrives, your artichoke seedlings will require some fancy temperature- related attention. If one starts seed in January, the transplants will be ready to be planted out by the end of April, but they must be vernalized first – a fancy term for exposing plants to considerably cold temperatures for a few weeks – recent tests by Oregon State suggest that the idea vernalization could be exposing plants ( seedlings) to temperatures at about 40º F for 2-4 weeks to achieve proper vernalization ( other studies suggest that seeds can be vernalized if moistend, for 4 weeks and 35-40º F, but exposing seedlings is easier).”
Rootrainer ™ Seedstarters Encourage Healthy Root Growth
- Grooved growing cells promote healthy, downward root growth
- Roots don’t spiral, so seedlings transplant better than pot-bound seedlings
- Growing cells hinge so it’s easy to remove plants without disturbing roots
Rootrainer seedstarters have grooved cells that promote downward root growth and discourage spiraling, yielding deep-rooted seedlings that transplant easily and adapt quickly to the garden. Cells are 1-1⁄2″ square at the top, and they hinge so you can monitor root growth and remove plants without disturbing roots. Made from plastic; may be reused. The Deep Rootrainer has 32 cells with a holding frame; no waterproof tray or cover. $19.95 On Amazon $15.19
The same effect may also be attained with water bottle and cut the plastic off the root.
Growing Artichokes from Seed is easy, just be sure to do the right thing at the right time
“Here is my method [Matt’s]:
• I first pre-soaked for 24 hours to soften the seedcoat
• Seed is sown 1/4 -1/2 inch deep in RootTrainer pots in mid-January
• Seed tray is placed under lights with bottom heat at 74º F. until seedlings emerge ( 10-14 days)
• Seedlings are transferred to a heating mat in the cold greenhouse after a month indoors, were temps near the roots are kept at 75º F but air is maintained at 50º.
• Seedlings are fertilized bi-weekly to encourage strong growth
• Plants are brought outdoors on cool days starting in mid-march, and only brought in if temperatures drop below 32º at night ( to a porch – one must not bring them back into the warm greenhouse once vernalization has begun, for plants must believe that it is winter in northern California for at least two weeks – keep temps below 40º – it’s not as hard as you may think, use a cold porch).
• Plants are set out into the garden in rows that are 3-4 feet apart on May 1.”
If you live in a climate colder than Zone 8, your best bet is to start new plants each year. If you have a mild winter and mulch well, the artichokes may survive as perennials. Remember, it’s the artichoke’s roots that need protection.
Using transplants, you can grow artichokes as annuals in cold-winter climates with 90 to 100 frost-free days. I know people who have grown delicious artichokes in Connecticut, Maine, and Massachusetts. Artichokes you start indoors in late winter or early spring will be ready to harvest from late summer through early fall.