This morning I read a Facebook post written by a friend, Joshua B. He wanted to know how to hold over artichokes where winter temperatures drop to zero and below. I thought this was the perfect opportunity to explore climate zones, plant origins, and plant life cycles discussed earlier in this blog.
Artichoke (Cynara scolymus) is a Mediterranean native and a perennial. This tells us that it is found in climate zones 7 and 8. Climate zone maps most often deal with minimum temperatures and I will list several examples here:
Zone 5 = -20 degrees to -10 degrees
Zone 6 = -10 degrees to 0 degrees
Zone 7 = 0 degrees to 10 degrees
Zone 8 = 10 degrees to 20 degrees
So you can see that an artichoke’s ability to survive the cold has a great deal to do with your particular climate zone. The USDA Plant Hardiness Zone Map indicates temperature ranges down to individual counties and includes sub-zones of 20 latitude and longitude lines. www.usna.usda.gov/Hardzone/ushzmap.html
And there are climate zones, unnoticed micro-ecosystems right in your own yard. Having a minimum/maximum thermometer and keeping a record will in time show you areas of your yard that can be both warmer and colder than a climate zone map would indicate. For example, a wall with good sun exposure in the winter actually creates a warmer climate. It stores heat during the day and releases heat at night. You can take this knowledge and run with it, enhancing the warmth of that particular spot with floating row covers and things like that.
So let’s look at the artichokes themselves. As a perennial an artichoke might not produce the first year or what is produced doesn’t amount to much. It needs deep, nutrient rich soil and an abundance of moisture. Artichoke can be propagated from seed or divisions in the spring. It is slow to make up and seed must be started under lights by mid-February. After all danger of frost, bed out the starts two feet apart and immediately feed with organic fertilizer and top dress with about 4 inches of compost. An earlier post addresses how to use and capitilize on grow lights. Another post discusses plant life cycles, perennial, biennial, annual, and draws the distinction of “tender perennial” based entirely on the climate zone of the species’ place of origin. Artichoke is considered a tender perennial in most of the US.
If your winter temperature drops below 10 degrees that fact makes artichoke a good candidate for container growing. In a previous post it makes the case for bringing tender perennials inside and holding them over in a cool place but one that never freezes. If you think that your artichokes have a good chance of survival outside, prune them back to about 6 inches and cover them with about 2 feet of leaves, prunings, grass clippings, etc. Now, we have all seen the road signs that say “Bridge Freezes First”. That’s true of containers and raised beds as well. Both can freeze solid even when the ground, just a few inches below the surface does not freeze at all.