Water and light are essential to plants, and in a greenhouse you'll have to provide both. There are several different watering methods to choose from: hand watering, capillary mats that bring water up from below, overhead watering, and drip irrigation that delivers water directly into each pot.

Greenhouse expert Scott Naegeli says a drip irrigation system is easy to lay out and is very cost-effective. It delivers small amounts of water over long periods of time, so plants stay uniformly moist. Installation is fairly simple:

• Be sure the mainline that carries water into the greenhouse is sunk underground at least four feet, which is below the frost line, to make sure the water in the line doesn't freeze.
  
  
• Use a 3/4-inch poly pipe as the water supply line. Position it to run down the length of the bench.
  
  
• From the main line, connect lateral lines to run between pots.
  
  
• Set the system on a timer to ensure regular watering.

Once the water system is in place, you'll need to address any lighting needs. Although fluorescent lights are popular, they help the gardener more than the plants. This type of lighting is good to work by, but plants need more light, especially in northern regions.

A high-pressure sodium bulb does a better job of simulating sunlight to stimulate plant growth. A 125-watt bulb gives off plenty of light when hung at least three feet above plants or seeds. This is a good distance to avoid heat burn.

Grow lights help to lighten shady spots and propagation areas in the greenhouse. What you are germinating or propagating determines how long you need to leave the lights on, usually an average of 12 to 16 hours each day. If you are growing tropical plants, you may need to set up grow lights if the plants don't get at least eight hours of sun each day.