Have you noticed lately that your spruce has white-tipped or brown needles? Rachel Allison, western forest health assistant with the Nebraska Forest Service noticed this when traveling in western Nebraska as well as in the trees near her office in North Platte. She explained that understanding where spruce trees prefer to live tells us a little about the cause of this problem.
The commonly planted spruces – Colorado, White, Engelmann & Norway – typically grow on north and east facing mountain slopes, usually at high elevations where snow
stays around for several months of the year. These high elevations make the trees cold tolerant, but the cold, moist conditions are very different from the hot, dry sites where many spruce are planted in landscapes and communities. Spruce prefer good, deep soil and growing among other trees that can protect them from hot, dry winds.
People often believe that spruce will do well in a xeriscape or low water landscape. But since spruce are adapted to a moist environment, the trees are often stressed from the dry conditions and competition with turf and other plants. In addition, spruce trees growing in low elevations with low humidity and high temperatures lose water through their needles faster than the water can be replaced by the roots. The stress caused by this lack of water in the needles often causes the needles to have a brown or purple cast, particularly during the summer when combined with the sun and heat. Right now, Allison notes, “the same situation happens in the winter, this time the lack of soil moisture leads to the white-tipped or brown needles. Both of these conditions are the trees’ way of showing us they need water.”
In addition, when spruce, or any plants for that matter, are planted in landscapes outside of their normal habitat or range, they can become additionally affected by poor site conditions, improper planting (usually planting too deeply), environmental problems, and insect and disease attack. Environmental causes are typically the biggest problems and commonly come from transplant shock, mounding mulch around the trunk, under or over watering, winter desiccation, frost damage, hail damage, salt toxicity, herbicide damage and nutrient deficiency.
Often a pest or an easily seen problem is pointed to as the cause of a tree’s poor condition, but the main long-term underlying problem is missed–that the tree is not suited to its environment. In order to help the tree adapt, we need to provide an environment that is more suitable for it. This includes planting the tree properly and at the proper depth, using a flat area of mulch in a wide ring around the tree that is not mounded up on the trunk, and watering properly. For spruce, watering is the most critical.
Trees compared to turf have root systems that spread deeper, typically down to 24 inches; and the best way to water is to do it less frequently but for longer durations. The amount of soil with good available moisture can be determined by pushing a long screw driver or slim metal rod into the soil until it stops when dry soil is reached. Allison has found that the depth to dry soil in a yard typically ranges from 1 to 6 inches, and rarely up to 8 inches, but none of these are adequate. The target for good available moisture is within the top 12 to 18 inches of soil. Watering to provide the deep soaking needed to accomplish this should be carried out once a week during hot summer months (July, August) and less frequently in the cooler months. As Allison explained, “all trees would really rather be watered once or twice a month with a good long rainfall, but when that doesn’t happen, we need to provide the necessary water ourselves.”
Trees typically do not get the water they need from an automatic irrigation system, because the system is set up to manage and care for the lawn, not the trees. The watering cycle is short and frequent, providing shallow moisture for turf, but not deep enough for trees. The amount of water needed by trees in your lawn and how long it takes to provide it depends on your soil type; usually with more water needed for sandy soils and less for clay soils. It is important to periodically check the level of moisture in your soil near the dripline of your trees.
If reducing the cost of water is a goal, you can actually apply less water and still maintain soil moisture at good levels by providing a level, mulched area around your trees out to the dripline of the tree. When mulch covers the soil, it helps to retain the moisture that would otherwise be pulled out by drying winds or from nearby grass.
The best advice when using automatic irrigation systems is to separate your landscape into different zones depending on different watering needs. Place spruce and other plants that need deep watering together. Water them deeply and no more than once or twice per week. Avoid daily, shallow watering that can cause problems by leaving deeper soil areas still dry.
For more information contact Elizabeth Killinger at firstname.lastname@example.org, 308-385-5088, on Facebook, Twitter, her blog at https://huskerhort.wordpress.com/, or visit the University of Nebraska-Lincoln Extension website: hall.unl.edu.