Well, this is one of the tougher question to answer when it comes to lawn care. It all comes down to the nature of the brown patches on lawn. For instance, the most common reason for a brown patch is drought. Yes, this kind of patch will usually spread, depending on the length of the drought. Also, saving the lawn depends of how severe the drought was and how long it lasted. Usually a good watering can do the trick. But if the drought was more than a couple of months, than the problem might be harder to fix.
Another reason for brown patches on lawn can be dogs. Pets using the lawn to do their business can leave the grass with brown spots. These usually don’t spread. They remain confined to the area the pet used. However, if the uses the same spots multiple times, this can lead to damage to the soil. Watering your grass and teaching your pet to use a different spot usually works.
But sometimes watering can actually be the reason for brown patches on lawn. If the lawn is watered too shallow, it can cause it to have weak roots and not withstand summer heat. Also, watering it too frequently can lead to it effectively drowning. Test first if your grass needs watering. Only do so if it looks wilted or if it doesn’t pop right back up if you step on it.