A rooftop garden is a great asset if you live in an apartment or have a flat roof with limited yard space. There are a few irrigation methods that can fit every situation and budget. Here are some tips and suggestions for different rooftop garden irrigation systems and how each one can be applied most effectively.
Be sure that anything you build on your roof is properly supported. Avoid concentrating a lot of weight on small areas by using wood or PVC frames that can evenly distribute the weight over a larger area. Without the proper support, your roof could leak or even collapse, causing a great deal of expensive damage. This is especially true of water storage containers, which should be placed over load bearing walls whenever possible.
The best green roof construction will provide a recycling irrigation system that maximizes natural conditions. This includes capturing rainfall and pumping it back out for irrigating the rooftop garden, but it also includes reclamation of excess moisture in your planting beds. Starter systems are available at major hardware stores and garden centers, or you can pick up a wide variety of D-I-Y plans.
A drip irrigation system provides a consistent amount of water to minimize loss. Instead of a destructive splattering, the moisture is slowly released into the soil. Drip systems are the most efficient type of irrigation systems, but they also have a higher initial cost, and require regular maintenance. For young or tender vegetation, drip systems do not cause damage to the leaves or stems, and it can be adapted for any level of soil moisture.
Ordinary Sprinkler systems are not very efficient, and should only be considered as a last resort for most situations. Alternatively, sprinkler systems include misting devices which pressurize the water and emit it as a fine mist of droplets. This type is much more efficient, but has a very high evaporation rate in dry climates. Sprinkler systems are probably the most affordable and simple method to install, but they are very difficult to use for precise water control.
You can use rolled tubing and create a simple irrigation system. Drainage can be directed to a central recycling container where it is strained and pumped back out onto the plants. Debris that is sifted out can be redistributed over the rooftop garden. Use an inexpensive pump to create water circulation, and set it on an ordinary wall timer.
When to Water
No matter what method you use, there is a time for watering. Never apply water to plants during the middle part of the day, because it can cause them to burn or wilt. A good rule of thumb is that watering should not be done from 3 hours after sun rise until 3 hours before sunset. In dry locations, the best time for watering is in the evening, which gives the plants and soil plenty of opportunity to absorb moisture before the water can evaporate.