Vegetable seeds should always be sown thinly and evenly to reduce the risk of competition for light, water and nutrients between the growing seedlings. They should be sown at a depth relative to their size; a good rule of thumb is to cover the seed to a depth equal to 4 times the diameter of its largest dimension. For example:

• Onions: 1 cm (1/2 in) deep
• Cucumbers and tomatoes: 2 cm (3/4 in) deep
• Peas: 3 cm (1 1/4 in) deep
• French beans: 4 cm (1 1/2 in) deep
• Runner beans: 5 cm (2 in) deep

Constant moisture is essential for successful germination. The soil can be kept moist until the seed germinates by placing plastic sheeting or newspapers over the surface after sowing. However, you must make sure that this is removed as soon as the seedlings begin to come through the surface of the soil.