The trees in our neighborhoods contribute a great deal to our daily lives: they lower stress, reduce rates of asthma, and even mitigate some of the effects of climate change by lowering ambient air temperatures and soaking up rainfall.
The trees that grace our gardens and sidewalks need water. In our enthusiasm for saving water, we don’t want to forget to provide proper care for our trees. That’s especially important during the hottest and driest months of July, August, September, and sometimes in October. Here are some tips for how to care for yours.
The amount and placement of water are dependent on the age, size, and species of the tree. All trees need periodic watering, but different species may vary in their irrigation requirements. For example, native trees such as live oaks, which are adapted to a drier climate, are vulnerable to overwatering. These tree species may benefit from a soaking no more than once or twice during the dry season. Species with higher water needs may benefit from a monthly or even biweekly watering schedule. Be sure to research the specific needs of your trees. A good place to start is this tree library and watering guide from Canopy, a Bay Area-based non-profit focused on urban forestry.
Watering young and newly-planted trees
Trees between one and three years of age generally require five to seven gallons of water per week for each inch of trunk diameter.
Focus water on a young tree’s root ball. Form a temporary earthen berm, a small ridge that forms a well around the tree. Fill it slowly with a garden hose set at very low flow near the base of the trunk, and then let it absorb into the soil. As the tree grows, the berm should be expanded to encourage the roots to grow out and away from the trunk, and then be removed altogether. Irrigation bags are also effective in watering newly-planted trees, but only for the first two to three years after planting. Roots must be encouraged to grow out and away from the trunk.
How to water mature trees
Mature trees require between 10 and 15 gallons of water for every one inch of trunk diameter measured at breast-height (about 4.5 feet above the ground). How often you water your tree depends largely on its species. Check Canopy’s tree library and watering guide for your species’ specific water needs. The majority of nutrient uptake and moisture uptake happen around and beyond the “dripline” of the tree. The dripline is the zone beneath the edge of the tree’s farthest branches. Imagine a wine glass on a dinner plate, with the edge of the glass’s base representing the dripline. Watering should happen between the edge of the wine glass and the edge of the plate, said Mike Oxendine, founder and director of OUR Community Forestry.
When is the best time to water?
Composition and permeability of soil can vary widely, even across the same property. Check the soil before watering. To determine whether or not your tree needs water, use a spade to open the ground at least four inches deep and check for moisture with your hand. The surface will dry out much faster. If the soil below ground is still very wet to the touch, water less. If it is dry to the touch, it is time to water. Soon, you will become familiar with how much water each of your trees needs.
When should trees be watered?
Ashland experiences its hottest and driest weather during the summer months of July, August, and September. However, June and October can also get hot and dry. Generally, if there has been no precipitation for one week, your newly planted trees will need watering. If there has been no precipitation for a month, begin watering your mature trees.
The importance of mulching
Ever wonder what to do with all the leaves that litter your yard? Mulch! Mulching is the practice of covering the soil with a layer of material to improve the soil and protect plants. Mulching reduces soil moisture loss, insulates soil, protects roots from extreme temperatures, and improves soil fertility as the mulch decomposes. A four-inch layer of mulch, kept one foot away from the trunk, slows evaporation, keeps the weeds down, prevents a hard crust from forming on the soil surface, cools the root zone, and creates a healthier environment for the beneficial microorganisms in the soil.
Note that organic mulch, like leaves or bark chips, are a fire hazard during those drier months, so don’t use any within five feet of a building. (Inorganic mulch, like pea gravel, is fine to use in this zone.) It’s also for that reason you’ll want to leave some space between the mulch and tree trunk. Better yet, compost your leaves (and maybe throw in a few food scraps!) before laying them down as mulch — finished compost is much less flammable than leaf mulch.