Leeks all fall under the species Allium ampeloprasum, but this divides into two subspecies: porrum and ampeloprasum (not a typo. It’s literaly Allium ampeloprasum var. Ampeloprasum. In other words: it best represents the species).
Porrum covers common garden leeks, whose thick shanks, and sweet, mild flavor we so love. They dependably bloom and make seed their second year from sowing. Sometimes they make side bulblets, creating a clump of progressively smaller leeks if not divided. This clump can come back year after year. The variety “Babington’s” leek is especially well know for this habit.
To be happy, though, they need pretty rich fertility; and really propagate best by self seeding. Winter quite dependably squelches these tender things in my climate. For all practical purposes, I consider porrum cultivars to be annuals.
Elephant garlic and the like are the true ampeloprasums. When you find sources online trying to pass off “perennial leeks,” they are more than likely from this corner of ampeloprasia. You’ll notice, as you chop them, a smaller diameter, and a more prominent garlic fragrance and flavor than usually found in the porrums. Variety anpeloprasums readily divide themselves every year, like garlic. Similar to the porrums, the individual plants get smaller as the clump gets bigger. I have yet to see these proficiently seed themselves; but winter here can’t dig its claws into this hardy plant, so there’s little incentive.
“Oepri perizweib” is a variety of perennial leek I grow. I got it from Southern Exposure. It has a mild garlic flavor. I don’t divide them, resulting in thick clumps of little sprouts I usually just snap off rather than digging. This leaves the bottoms to regrow. Doesn’t seed so far as I can tell. It rarely even blooms when clumped together. If spaced well, and given fertile conditions, they can reach close to an inch across at the base. Below is a fine clump with Mache as a groundcover.*
Another specimen I would say resembles these ampeloprasums is the Sacred Forest garlic Oikos Tree Crops sells. Its scapes are characteristic of the ampeloprasums, although they list it as a garlic (A. sativum). It has also proved quite hardy for me. I’ve found it is quite slow to form new side shoots where I have it, but these are about as large as the parent -no shrinking. This is in stark contrast to the Oepri Perizweib. It’s also much larger than the healthiest, most pampered of the Oepri’s I’ve grown; so perhaps give this one a try and let me know what you think.
I prefer to keep the perennial ampeloprasum leeks for their hardiness, and because they sprout up as early as late February for me. They die down around June and July, but will often start up again once the weather cools around September. Below are some of the Oepri and mache I harvested in February.
As with the other alliums in this Perennial Alliums series, you could keep any of these ampeloprasums in a perennial border as clumps, then divide and separate every year for growing out in well spaced, fertile soils to get larger size and milder flavor. Let nature manage propagation. The porrums might find such uncouth settings unaccomdating; so perhaps give them a little richer spot, or try them in a greenhouse planting. It would certainly keep the leeks flowing all season long.
*If you are drawn to growing effective goundcovers like this, may I suggest you take a look at Mastering The Growing Edge. I wrote it just for an interested gardener like you.