Leeks (Allium ampeloprasum) belong to the allium family, which also includes garlic, chives, and onions among its members. Understanding the family a plant belongs to helps to understand more about the behaviors and characteristics of individual members of that family, and how to grow them better in your garden. (Learn more about the allium family.)
Leeks are seed-producing alliums. They have perfect flowers, but are outbreeding plants (they can not self-pollinate). They will cross-pollinate only with other leeks – whether of the same or different variety.
Leeks are biennials – they need two growing seasons in order to reach the seed-producing stage.
The first year, leeks are usually planted in the spring, dug in late fall and heeled in buckets of dirt or damp sand in a cool cellar. They are replanted in the spring, at which point they’ll send up large globe flowers and set seed. Leeks will send up flower stalks after experiencing cold temperatures for at least 4-6 weeks, regardless of the day length, unlike other alliums.
Give them as long a season as possible for the seed heads to mature. If necessary, you can cut the seed heads from the plant and hang them upside down in a brown paper bag to finish ripening. The seed heads of leeks are less prone to shattering than other alliums, and can be left in the garden longer without the worry of losing the seed.
In places with mild winters, where leeks can be left in the ground all winter long, especially with a good layer of mulch to protect the roots. When leeks overwinter in the ground, they’ll often produce little bulblets, more accurately known as ‘leek pearls’. These pearls can be retrieved and replanted. Since these are a vegetative reproduction of the plant and not a sexual reproduction (as seeds are), the pearls are genetically identical to the parent plant. This method of leek reproduction is especially useful in cases where the seed may have become contaminated.
Elephant garlic is of particular note here, as it is actually a type of leek. (Bulb or multi-centric divisions, flowers, etc.). For further reading on Elephant Garlic, click here.