If you feel like your plants are not looking particularly healthy, the most likely reason is probably due to the unusually dry summer season we have been having. Recorded data has rainfall for September this year at 0.78 inches which is 2.45 inches below normal. That makes this past month the 5th driest September on record. Just walking through the neighborhoods it is apparent that even old established trees and shrubs are showing signs of lack of water. Droopy leaves and brown grass are pretty much commonplace.
While we are expecting some rain this weekend, we cannot expect that will be enough to help the plants completely recover. For one, counterintuitive to what one might believe, dry soil does not absorb and hold water well. Water tends to pass through hard cracked soil and is not immediately held to be available for the plants to absorb. Typically if soil is dry we recommend applying water in a slow repeated application to allow water to gradually absorb. Watering using a sprinkler or a soaker hose is the best approach to achieve this. If we only get a flash of heavy rain, there is a good chance the soil will not feel wet for long and will benefit from additional watering over the next week.
Secondly, the plants need consistent periodic water all the way through the fall until the ground is frozen. In Chicago that could mean you may need to water well into December if previous winters are any indication. Even if air temperatures at night are in the 30’s, if daytime is in the 40s and 50s, there is a good chance the ground is not actually frozen and the plants will still be taking in moisture.
This is especially true for evergreens which can be particularly deceiving because they will be dormant and look green throughout the winter even in an under-watered state, and will only turn brown once we warm up in the spring. If you have ever noticed an evergreen suddenly go brown within the first few weeks of spring, you are likely witnessing the result of not enough water over the course of the winter.
Watering into the cold weather does not have to be as often but is recommended at least a couple times a month if there has been no snow or rain. If you have already turned off your water outside for the season expecting frost, you can always water by dumping a bag of ice under your evergreens. As the ice melts it will provide the slow drip of water that will sufficiently provide the moisture the plants need.