Keep in mind that even though the temperatures have reached any icy point, it usually takes several days of freezing temperatures to do significant to your landscape. Of course, its helpful to cover what you can especially natives, tropicals and tender foliage like ferns and grasses.
More importantly you will want to consider preparing you irrigation system. There are steps that should be followed to empty your vacuum breaker. You then should make sure the system is off. You will have to then re-pressurize the breaker before the system can be utilized again.
Call us or a professional irrigator if you need help with this or experience a break. Stay warm!