Linn County Master Gardener, Becki Lynch, addresses guidelines for watering at this time of year:
Fall is normally the best time to plant and transplant shrubs, trees, and perennials. Unfortunately, this year we can’t depend on the temperature and moisture to be the same as year’s past. We’re in a drought situation, so instead of heavily depending on nature to provide the moisture needed, we must make sure we know how much water to supplement. Below are the accepted practices, which could be supplemented to natural rain in order to keep young plants healthy going into winter.
First, what is the general watering guideline for trees and shrubs?
Because trees and shrubs are the backbone of your landscape, watering should be a high priority for any that are new up to about 7 years in age. Conifers are particularly susceptible when they are young and should be watered as long as temperatures permit. Most want consistent moisture and well-drained soil. In drought conditions, the general guideline for watering young trees and shrubs is 10 gallons per inch diameter of trunk of tree every 7 to 10 days. Go ahead and apply directly below canopy around trunk as the root system is concentrated there for any first and second year trees and shrubs.
Second, what is the guideline for flower/perennial beds?
The overall general guideline is 1 inch per week of water, but what does that mean? And how do you measure it? In translation, 1 inch is approximately 10 to 12 inches of moisture penetration (soaking) into the soil around the plants. To determine what that means for your home, simply turn on your method of watering and run for 15 minutes. Leave it alone for 24 hours, and then dig down and measure how far the water soaked in. Divide 12 by depth measurement to determine the multiplier for 15. For example: Depth = 4 inches; 4 divided by 12=3; 3 x15=45 minutes. To be applied once every 7 to 10 days.
Third, how long should the watering occur?
That’s very simple – new plants should be watered through a hard frost, when the plants and trees/shrubs have become dormant. This practice will make sure they have developed a strong root system prior to dormancy and have plenty of moisture to draw on in the spring.