There are few factors that go into deciding when to stop watering your lawn as fall and winter approach. Amongst other things, the biggest deciding factor in how long you continue to water your lawn after Labor Day is obviously your location and climate.
If you live in the southern part of the country you will probably continue to water your lawn the entire year. When temperatures cool in these areas you can water your lawn less often, but you should not cease all irrigation. It is very important not to overwater since cooler temperatures make the growth of fungi easier which appear in your lawn as dead or bald patches.
The rule of thumb for stopping irrigation completely for cooler climates is when the ground freezes. This makes sense as the frozen ground becomes a barrier to your root system. Also, as soon as the ground freezes grass becomes dormant. Even if the frozen ground temperature for a few days then there are a few days that are warm before going back to frozen, the ground will not thaw completely to awaken your grass again. The fall is a very important time for your lawn, while growth above the ground slows, beneath in the root system your grass is growing.
Depending on the type of seed that you have used, fall might be the biggest growth for your lawn the entire year. Again, you’re not going to see it and you’re not going to have to mow the lawn every week like in the summer. But beneath the top soil your grass is preparing for next spring. To grow a nice, thick, healthy looking lawn autumn watering is critical. If you stop irrigation as soon at September hits before the ground is frozen, the preparation in your root system will not happen. Not as much water is needed since water does not evaporate as quickly as it does in the summer, and it is not needed as often. You might be able to get away with once a week if the temperatures are cool enough, but still above freezing. Monitoring of moisture is important in the fall, too much moisture can lead to fungi growth which will jeopardize the fullness of your lawn the coming spring.
Fall is the time to fix any bald or seriously damaged patches in your lawn. These will need to be watered regularly and you might not even see grass spring up before a freeze, but you have laid the ground work for the coming spring.
It is also important to remember that fall leaves and cooler days are not a signal to cease other lawn care as well. It is important to keep up on your mowing, which will not have to be done often due to the slow in growth above ground. But it is a good idea to have one last mow before the ground freezes to give your lawn a head start for the next spring.