To water your plants, you should install irrigation systems. These are basically small pipes that run underground and slowly release water into the soil – greenhouse models are very similar to the ones used on commercial farms, only smaller. These irrigation systems allow you to quite simply and easily set how much water your plants are getting with a tap, instead of you having to go and water them all by hand. Many plants will also respond better to being watered at the roots than they do to being watered on the topsoil, and they will often grow bigger, which is an added bonus.
The other thing you need is a cooling system. While it might seem odd to have a cooling system in a greenhouse, it is possible for them to get so hot inside that all the plants will get cooked and die, especially in a hot summer. Again, the cooling system will be a series of underground pipes, allowing hot air to be taken down underground and stored during the day, and then released when it is cooler in the night.
While greenhouses might seem to be quite basic things altogether, though, there’s nothing stopping you from going all high-tech with them. More advanced systems have electronic climate control, allowing you to set the exact temperature of your greenhouse, and will open and close underground tubes and other escape routes for hot air in order to keep the temperature in your greenhouse tightly controlled. This can be useful for growing plants that only do well in one specific climate, such as some kinds of tropical flowers.