I was recently very lucky and visited Jerry Coleby-Williams' amazing garden at his home; Bellis. Not only is Jerry's garden inspiring, but so is his generosity - I (along with many others) received several Multiplier (perennial) Leeks that Jerry shared with visitors. Since planting these leeks, I have been quite surprised at how quickly they have grown and multiplied. I will certainly be propagating more and following on with Jerry's philosophy and generosity by sharing them with other like-minded people.
I hope the following growing guide helps:
Young seedling offshoots develop at the base of each plant. Upon lifting the planting from the soil with a garden spade, the young offshoots can easily be separated from the parent plant.
Each seedling should be planted quite deep, but how deep will depend on the size of the young plant - ensure that the roots are well buried, with a good section of stem also below the surface - keep the leaf junctions above the soil surface. This will help with the "blanching" of the stem as it grows, resulting in the development of a large white stem (best used in cooking) rather than a mostly green stem.
Leeks like a slightly acidic soil, a pH of approximately 6.5. A good supply of nitrogen is also desirable for optimum growth, so a sprinkle of chicken manure can be a benefit. Before planting, ensure that the soil is well conditioned with manure and compost. Lastly, leeks don't like dry soils, so ensure that they are well watered in and the soil kept moist with regular watering and a good layer of mulch.
Hopefully, the following video will help: