The most important factor in growing competitive show leeks is to start with an established variety that produces impressive specimens. Most show leeks are pot leeks that require about three months in the ground to reach full maturity. This means that if your show is in September, you should plant your leek starts in late May or early June to have fully grown leeks at show time.
Start show leeks in pots, and harden them off in a cold frame for a week before planting them in the ground outdoors. Alternatively, you can grow individual leeks to maturity in pots; just be sure you use pots large enough to accommodate the specific variety you are growing. However, most show leek growers choose to grow leeks in a specially prepared bed called a leek trench.
Prepare a leek trench by laying down ashes or crushed stone directly onto the top of the soil. For the next layer, use wood chips or bark mulch to provide the leeks with effective drainage. Finally, add a layer of compost or manure, and mix this with an equal amount of high-quality topsoil. The complete trench should be about 18 inches above the regular soil level.
Construct your leek trench in a sheltered area of the garden, as high winds can destroy delicate leek leaves. While leaves do not matter at show time, as judges only consider the lower portion of the plant, healthy leaves are essential for ensuring the leeks grow healthy and large.