Leek varieties can be differentiated based on their speed of growth, length of stem, and winter hardiness. Typically, early varieties are smaller but have a faster growth cycle, whilst later varieties take longer to mature and are harvested through winter and early spring. Newer varieties of leeks have been introduced, sometimes as hybrid F1 types, that combine the advantages of both.
Leeks are easy to grow and will mature to harvest in a wide range of soil types. They do not take up a lot of space in a garden or allotment, and can be grown relatively close together and tolerate some shade. Their ideal growing conditions are rich soils that have had well rotted compost mixed in, with a soil that holds moisture but is free draining (ie no puddles). In these conditions, leeks will develop longer stems and mature faster.
The main choice facing a gardener is the time of harvest they prefer. My preference is to grow leeks for winter and spring picking, rather than for a late summer and early autumn crop. My reasoning is that in late summer there are many other vegetables available for harvest, including garlic, onions, and shallots. In winter, and especially early spring, there are far fewer crops available. Leeks come into their own during this period, as they are extremely hardy and can be left standing on the plot until needed.
The only growing difference between early and late leek varieties is when to sow them. Early varieties are sown when the weather warms in the spring, whilst late maturing varieties are sown towards mid-year. Early varieties will mature more quickly for a harvest in late summer and autumn, whilst late varieties will mature in autumn for harvesting through winter and early spring.
Leeks are slow growing, and I find it easiest to sow seed into a seed tray or garden planter. Using fresh compost is a time saver, to avoid having to weed around the seedlings as they germinate. When the seedlings are about 15 centimetres or 6 inches tall, they are ready for planting in their final growing positions. To save weeding, I plant the seedlings though holes cut into biodegradable weed fabric. To grow longer white stems, I create cylindrical holes in the ground about 15 centimetres or 6 inches deep, by pushing the handle of a hand trowel down into the soil. One leek seedling is placed in each hole, before filling the hole with water to help bed the roots in wet soil.