Which method is essential for effective watering in greenhouse cultivation?

The use of a well-drained substrate is essential for effective watering in greenhouse cultivation because it helps prevent issues related to overwatering and root rot. A well-drained substrate allows excess water to escape while retaining the necessary moisture that plants need. It creates an optimal environment for root development by ensuring that roots have access to both air and water.

In contrast, some of the other methods listed can lead to complications. For instance, watering only when the soil feels dry may not provide consistent moisture levels, as plants may suffer from drought stress before the soil reaches that point. Watering at night may lead to prolonged moisture in the substrate, which can foster fungal diseases. Lastly, while watering with soft water can be beneficial in specific situations, it is not universally essential for effective watering. The overall health of the substrate and drainage system is far more critical for successful greenhouse cultivation.