Growing huge leeks is just a big ego trip! So here's how to do it!
1) Select a huge variety: Scratch that. Select a number of huge varieties. Products, you may have noticed, are not always as advertised. So, grow several to find one that preforms. Also, do you want length or girth? Usually you will be trading one for another to some extent.
2) Select a variety that is hardy enough for your climate: Leeks require a long season to grow big. If you have extreme winters, leeks may not survive in open ground, but select a hardy one anyway and you can cover it a bit to keep it alive and growing. (See Eliot Coleman's Four Season Gardening for techniques to keep your garden growing through the winter in cold climates). The short varieties seem to be the hardy winter types. My favorite, Bulgarian Giant, barely survives winters here in the low 20's, but plenty still make it through and I select seeds only from those. Very cold climates will probably dictate growing the stubby flag types unless significant protection is used.
3) Start early and keep 'em movin': Leeks grow slowly, so start your leeks in January, February at the latest. They are also tough and they will survive considerable neglect and crowding. But, if you want big leeks, keep them growing by thinning and transplanting into a new flat once they get big enough to really select out the largest ones.
4) Hand Select the Seedlings: I've planted large, v.s. small starts in separate batches to confirm that indeed selecting large seedlings does make a difference. Whether the effect is one of genetic potential or environmental circumstances is open to question at this point and would require a different and worthwhile experiment. I start by sprinkling the seeds in a pot and sifting 1/2 inch of soil over them. Use good flat mix. Its hard to find good flat mix and better to make your own from some tasty homemade compost.
5! Thin early: I'm ruled by practical concerns like food production, so I plant leeks as close as 6 inches and up to 8 inches apart in every direction (i.e. in a wide bed on a grid pattern in staggered rows as opposed to traditional rows). However, I start thinning the small, stubby and crooked leeks to eat in early summer. If you want the super largest plants ever, you should plant them farther apart in the first place. I'm a fan of equidistant grid spacing in wide beds, so I would probably go with 14 inches apart in every direction. If planting closer as I do, thin early so that the plants are well spaced by late summer.
6) Keep feeding those suckers: Leeks have a hearty appetite. top dress them with blood, fresh manures, compost, seaweed, coffee grounds, or whatever ya got. Liquid fertilizers will go a long way too. If you do any of your own slaughtering, blood mixed with water will please your leeks greatly. Urine mixed with water will rock them into orbit. Any manure teas should also be good. Feed them something at least every month or so. I don't dig my beds, but if you do you would probably want to dig a bunch of stuff into the soil like manure or compost etc... but don't rely on that to get your leeks through their long growing season, keep feeding them...
7) Grow for as long as possible: No matter what you do, leeks take time to get their biggest. In the spring they will bolt, so they can't keep growing forever. The longer you can grow them though the bigger they will get until they decide its time to go to seed in the spring.
8) Save your biggest leeks for seed: Don't eat your biggest leeks! You can transplant them if they are in the way, then let them go to seed which will take most of the rest of the season. Try to save at least six plants just to prevent inbreeding. When the seed heads are pretty dry, pick them and dry them further and put them in a jar in a cool place. If you do this for a number of years you will have a strain that is adapted to your environment and tastes! And hopefully huge!
SEE ALSO: , Leeks: Size does matter!