In
order to get a succession of crops to harvest - and to prevent
periods of glut and famine - it is necessary to make frequent
sowings throughout the growing season.
In spring, when soil conditions are more consistently moist and temperatures aren't too high, sowing seed directly into the soil is relatively straightforward. However, when attempting to sow during the summer months, soil conditions are often too dry to ensure good germination and even seedling emergence.
One way to avoid this difficult period is to use transplanted vegetable crops. These can be germinated in the protected environment of a glasshouse or windowsill, where growing conditions can be monitored and controlled more easily. However, some crops such as radish, carrots and cut-and-come-again crops are more suited to direct sowing.
One way of improving your soil's moisture retention properties is to incorporate plenty of organic matter into it, ideally the autumn before sowing.
When preparing your summer seedbed thoroughly water the site the day before sowing, so that it is moist to a depth of at least 5cm (2in). This will ensure that the soil's moisture levels are sufficient, making the ground less likely to dry out in any dry weather immediately after sowing. Rake over before sowing to obtain a fine tilth, ensuring that the seed makes good contact with the soil and therefore soil moisture.
If you haven't had time to pre-water your seedbed water the base of the drill thoroughly, allowing water to puddle. Once drained sow the seed and then cover with dry soil, firming with the back of a rake or trowel to ensure good contact. Lining the drill with moist compost will also help.
If sowing large seeds, such as peas and beans, the drills can be make slightly deeper than usual to hold the seed away from any dry surface conditions (small seeds should be sown at their usual depth).
Some crops (notably lettuce) don't germinate well at high soil temperatures and this can be avoided by sowing in the afternoon so that the temperature-sensitive phase of germination is completed at night. If your soil is prone to 'capping' (developing a hard, impenetrable surface layer) backfill using compost rather than soil. To deter surface evaporation cover the drills with newspaper, hessian sacking or layers of horticultural fleece, checking frequently and removing the covering once seedlings emerge.