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 With a bit of care,
the plants will remain productive for 5 to 7 years in zones 8-10.
The plants can grow over 7 feet tall and make an interesting and
attractive addition as an edible ornamental in your beds and
gardens. They should be wrapped in paper and
have dirt mounded around them to over winter in cooler climates.
Harvest is enjoyed beginning in late spring to early summer.
STARTING
Start them as
seedlings indoors. The seedlings, when first planted out,
want to see about 8 to 10 days of temperatures around 50° if
they are to have a good growth; hereabouts, that means
planting out in mid-March or so. Since they
require a good 6 to 8 weeks indoors as seedlings before
being set out, we should sow seed around mid-January.
Starting
Seedlings
Sow your cardoon
seeds about ¼ inch deep and ¼ inch apart in a lightly
moistened soil-less growing mix. Use a good-quality starting
mix, not hardware-store "potting mix": you want a soil-free
medium, to be sure there are no fungal problems ("Jiffy Mix"
and "Pro-Mix" are representative examples of the sort of
thing wanted, and many mail-order garden-supply houses have
a proprietary mix). Germinate the seed at a temperature of
about 75° F.: heating pads or the like under the seedling
flat or pot are an immense assist to good germination. Be
sure to start more seeds than you want plants, perhaps half
again as many, because you will likely have to cull them at
planting-out time.
As soon after
emergence as the individual seedlings can be handled,
transplant them into fair-sized pots or cells--say 2 to 4
inches in size. Keep those transplants growing at
temperatures as close as you can get to 65° in the day and
55° at night; the day and night temperatures can be plus or
minus 5 degrees, but try to keep the day/night difference at
around 10°.
When the outdoor
daily highs hit the high 40s, transplant your seedlings out.
The Bed
Site your
cardoon bed where the plants will get at least 6 hours of
sun, as they will not develop properly without it.
Cardoons need
really good soil to thrive. Before planting out your
seedlings, spade the ground deeply (well-drained soil is
important), and supply it with good compost or manure (and
fertilize again, generously, every season). If your soil is
heavy (clay), work humus or even sand well into it. Slightly
acid soil is wanted for cardoons--some say even as acid as
pH 6.0 (though others say 6.5).
Transplanting
Out
We have seen
spacing recommendations from up to six feet down to 18
inches, which makes selection problematic. The optimum will
depend in part on your soil: the better it is, the bigger
the plants will grow. A test planting at small spacing,
especially in a deep-dug bed, seems logical, because you can
just pull out some if the lot is getting wildly overcrowded.
But in an event, this vegetable will eat up garden space.
Cardoons may not
always grow true to type from seed (they are commonly
propagated by cuttings); cull your seedlings before you
transplant: look for stunted or albino types and discard
them.
We want to plant cardoons out when they can get their first
days at around 50° or so, but, around here anyway, that can
expose them to freezes--our typical nightly lows in
mid-March are skirting the freeze line--which they should
not see. It thus seems wise to provide the seedlings with
some early night-time frost protection for their first
couple of months. Take care! Do not expose the plants,
especially at first, to daytime temperatures warmer than the
ambient. That means not just setting something like a Wall
o'Water on the seedlings and leaving it there. One approach
is to fill a number of transparent or translucent plastic
soda or milk jugs with water and leave them in the sun
during the day somewhere away from the cardoon seedlings,
then move the jugs around the plants at night so the
accumulated heat in the water softens the night-time lows
for the seedlings. (Moving Walls o'Water around on a
twice-daily basis would be far too tiresome.)
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