By Jeff Cole, Colorado Master Gardener

Why is winter watering so important?

You may have heard the mantra “water your trees during the fall and winter months.” In general, your trees and shrubs need about 1″ of water per month during the off season. If it does not snow or rain enough, you should give them water. But do you know why?

Trees have two types of roots: woody and fine feeder. Woody roots are the large roots and range in size from 1 cm to over 30 cm in diameter. Their function is to provide stability and to store nutrients and carbohydrates. They do not absorb much water or nutrients.

The fine feeder roots are quite different. They are very small. They can range in size from 10 mm to .2 mm in diameter! They live close to the surface. In our clay soils, 50% may reside in the top 4″. These small roots make up the largest surface area of the tree’s root system. They are the ones absorbing water and nutrients from the soil.

Feeder roots are short lived but are replaced regularly by a healthy tree. However, events like drought or extreme temperature swings can kill off large swaths of them. Low soil oxygen caused by overwatering can also kill off feeder roots. Winter watering not only keeps the roots alive, it also helps protect the roots from extreme cold because wet soils retain more heat than dry soils. So, remember to keep those feeder roots alive this fall and winter so that your tree is off to a good start next spring. Healthy trees are quite good at fighting off pests and diseases. For more information about roots, check out this article from CSU Extension called Watering Mature Shade Trees.