As the summer temperatures rise, everyone is starting to think about barbecues and enjoying their backyard more. There are two phrases that come to mind when I think about hot summer temperatures: the dog days of summer, and no landscape is complete without a tree. When temperatures get too warm, like dogs, people head for the cooling shade beneath the nearest tree.
Landscape trees in our area are extremely valuable for the many benefits they provide to homeowners, from cooling our homes naturally in the summer to protecting our landscapes from harsh winds and cleaning the air we breathe. Unfortunately, they also have to deal with many challenges, both from the environment and from the people who care for them.
If trees are not properly maintained, homeowners and landscapes will suffer as the trees decline and need to be removed. If you have a 50-foot blue spruce in your front yard and a severe rain and wind storm topples the tree, it can cost hundreds to well over thousands of dollars to remove it and repair damage to personal property. And that does not take into account that your replacement tree will take decades to grow to 50 feet.
Sadly, when it comes to our landscape trees, we make mistakes that may eventually lead to their demise. Unfortunately, trees are commonly planted in turfgrass areas, and homeowners water the tree the same way they water their turfgrass – shallowly. First big mistake. Most tree root systems, which are vital to tree survival, are made up of lateral spreading anchor and storage roots, with smaller feeder roots absorbing the majority of moisture. When trees are primarily watered by lawn sprinklers, the root system becomes shallow and closer to the surface, where the water is available. Frequently, this means most of the roots can be found in the top 6 inches of soil along with the competing turfgrass roots. Then, when rain saturates the soil and high swirling winds come through the valley, these trees can be pulled out of the ground, causing damage to homes and fences.
When watered properly, most urban trees will grow roots to 18 to 24 inches deep in the soil. Many homes have the issue of large roots from their or their neighbors’ trees creating mounds in the lawn. This is caused by shallow watering. Occasional deep watering will encourage new tree roots to grow deeper into the soil.
Another mistake in both commercial and home landscapes is allowing turfgrass to grow right up to the trunk of the tree. This results in what I call string-trimmeritis and moweritis. Young trees are especially vulnerable to string-trimmer or mower damage. Young trees have a very thin bark layer that protects their nutrient- and water-transport system. Once this layer is damaged, it can cut off the moisture and food supply, which will weaken or even kill the tree. To prevent damage to young and mature trees in turfgrass, apply a layer of biodegradable mulch or compost 3 to 4 inches deep beneath the tree’s canopy at least as far out as the tree’s drip line. The larger the area of mulch, the smaller the area where the tree and turfgrass roots can compete for moisture, and the less likely the tree will be damaged by lawn care equipment.
Since turfgrass and trees are the most common plants in our yards, it is important that we examine how the care of our grass effects the health of our trees. Unfortunately, these two plants do not work perfectly together. The natural grasslands of the Midwest have very few trees, and forests rarely have grass areas beneath the tree canopies. There is a reason for that – they have conflicting needs. In most cases when people water and fertilize, they are focusing on keeping the grass lush green and free of weeds, and not so much on keeping the tree alive. Frequent shallow watering, growth-stimulating fertilizers and weed killers can have a negative effect on tree health.
Trees need less frequent and deep watering. They require only small amounts of nitrogen fertilizer. Excessive nitrogen fertilization of trees causes weak and rapid growth, breaking branches and poor form. Standard lawn weed killers and weed-and-feed type products may weaken and kill trees when applied improperly. It is important to read product labels thoroughly to avoid damage to your landscape.
If you have weeds in your lawn, look at all the options to control them. Keep your lawn healthy to outcompete weeds, and mow high to shade out weed seeds. Spot-treat or hand-pull weeds for small infestations. For larger infestations, keep weed-killers away from the tree, remembering that tree roots spread far beyond the tree canopy.
As our season heats-up, take a few extra minutes each week to observe your landscape. Check soil moisture around your trees, using a long screwdriver to make sure moisture is penetrating at least 12 inches deep. If you feel you need to fertilize your trees, consider compost. Compost will feed the microbes in your soil, which will release soil nutrients as needed to your plants, and create a healthy ecosystem.
Helpful hints for planting new trees:
- When purchasing a tree for your property, make a point to research the area and the tree. Putting the right tree in the right place is crucial.
- Call 811 before you dig. Find out where underground power and gas lines are before you design your new landscape or start digging the hole for your tree.
- Don’t dig a 50-cent hole for a $500-dollar tree. Planting holes should be wide to encourage spreading roots and only as deep as the existing soil in the container. Avoid over-amending backfill soil as you want the roots to grow far beyond the planting area. Visit https://www.unce.unr.edu/publications/files/ho/2015/fs1502.pdf for more information.
- Don’t plant your trees too deep. The root flare, an area the fans out at the base of the trunk, should be visible above ground after planting.
- When watering your new tree, make sure the roots are encouraged to grow in all directions. You can do this by flooding the entire area under the tree canopy and creating a berm to hold the water around the roots, or by placing drip emitters so that moisture is applied on the north, east, south and west side of the tree. Flatten the berm and pull emitters away from the trunk as your new tree grows.
- Keep bark and rock mulches at least 3 inches away from the trunk to avoid rodent, moisture and pressure damage to the tree bark.
Wendy Hanson Mazet is a certified arborist and master gardener program coordinator for University of Nevada Cooperative Extension. Have questions about the health of your landscape? Contact a Master Gardener at firstname.lastname@example.org or 775-336-0265.