October 25, 2013

Establishing tree and shrub plantings can be time and labor intensive, making it important that landowners select the best species and practices to ensure long-term success. This can be especially challenging in western Nebraska where water is often limited and several years of droughts have left windbreaks weakened or dying.

 

Figure 1. Planting and watering techniques used in UNL tree establishment project. Drip line consisted of 1 inch UV tubing, woodpecker dripper, 16 mm UV tubing, plus a holding stake for the tubing.

 

To help landowners identify their best options, a UNL research study was initiated to examine factors affecting tree and shrub establishment in western Nebraska. Natural resource districts across the state offer a wide selection of trees and shrubs for windbreaks, wildlife habit, and to add value to property. In eastern Nebraska trees are common and comparatively easy to grow while in the west water is a growth limiting factor followed by species selection, site preparation, weed control, and planting technique.

Treatments Studied

To study how these factors affect establishment, a series of field experiments were conducted during the 2012 and 2013 growing seasons to compare the survival and growth of 21 tree and shrub species offered for sale by the North Platte Natural Resource District (NPNRD). Studies both years consisted of four treatments:

• trees watered on a weekly basis with a drip line.
• trees watered by hand once a month,
• weed control accomplished with landscape fabric covering 9 square feet around each tree,
• herbicides applied in a circular pattern to control vegetation in a 9-square-foot area around each tree (Figure 1).

Each of the four treatments was replicated eight times for a total of 32 trees for each species examined. In 2012, five tree and five shrub species were examined for a total of 320 trees; in 2013 a different group of six tree and five shrub species were tested for a total of 352 trees.

Site Characteristics

The experiment was conducted in a pasture in Scotts Bluff County approximately 200 yards from the North Platte River. The soil at the site is classified as alluvial and is composed of loamy, sandy, and gravelly soil. Precipitation at the site in 2012 was 6.3 inches, which was 36% of normal. Precipitation in 2013 was 6.8 inches by mid-August, which was 52% of normal.

The site was prepared for planting by mowing grasses and weeds in a 4-foot wide strip, digging a hole 1.5 feet deep by 8 inches in diameter with a post hole auger, and filling it with 2 quarts of water. The tree was hand planted, the soil was packed around tree roots, and the tree was watered with 2 quarts of water. Each tree and shrub was protected from weather, deer, and rabbit browsing by placing a 15-inch tall Protex plastic tube protector around the base of the tree. Trees watered with the drip line received 1.5 gallons of water per plant per week and plants watered by hand received 2 quarts of water per tree per month. Watering occurred in May, June, July, August, and September. Trees were planted on May 24 in 2012 and May 11 in 2013. Herbicides (Princep 90 at 2.2 lb/acre plus Pendulum Aqua Cap at 4 pt/acre plus Roundup PowerMAX at 2 qt/acre) were applied in a 9 square foot circle with a Solo backpack sprayer calibrated to deliver 20 gallons of water per acre. The tube tree protector prevented herbicide from contacting the tree.

Resulting Survival Rates

Trees and shrubs were evaluated in early August for survival and height (Table 1). Tree survival in 2012 ranged from 41% for Austrian Pine to 97% for Rocky Mountain Juniper; other survival rates were Black Hills Spruce at 53%, Black Walnut at 59%, and Bur Oak at 81%. Shrub survival ranged from 47% for Wild Plum to 81% for Chokecherry and 94% for Sand Cherry, Sumac and Golden Current. Spring rainfall was slightly greater in 2013 as was tree and shrub survival. Tree survival ranged from 69% for Colorado Blue Spruce, 72% for Native Cottonwood, 88% for Pondererosa pine, and 91% for hybrid cottonwood to 100% for Green Ash and Honey Locust. Shrub survival ranged from 88% for Gambel Oak, 97% for Wax Current, Nanking Cherry, and Wood Rose to 100% for Cotoneaster.

Trees and shrubs planted in 2012 were re-evaluated in 2013 to assess survival 15 months after planting (Table 1). Percent survival ranged from 25% for Austrian pine to 28% for Black Hills Spruce, 47% for Black Walnut, 53% for Bur Oak, and 84% for Rocky Mountain Juniper. Average tree survival dropped from 66% three months after planting to 47% 15 months after planting. Shrub survival 15 months after planting ranged from 38% for Wild Plum to 69% for Sand Cherry, 78% for Chokecherry, 91% for Golden Current, and 94% for Sumac. Average shrub survival was 82% three months after planting and 74% 15 months after planting.

Watering trees once a week with a drip line resulted in 88% survival three months after planting compared to 75% with hand watering once a month. Protecting trees from weed competition by using herbicides or landscape fabric was similar with 85% survival using herbicides compared to 79% survival with landscape fabric.

The best plant species for this site were Rocky Mountain Juniper, Green Ash, Honey Locust, and Hybrid Cottonwood. Shrubs adapted to this site were Sumac, Sand Cherry, Golden Current, Wax Current, Cotoneaster, Nanking Cherry, and Wood Rose. Tree and shrub survival will undoubtedly vary at different sites as soil characteristics and the local environment vary. Species such as Bur Oak, Black Walnut, Black Hills Spruce, and Wild Plum may have greater survival rates on upland sites.

Costs for Trees

Trees and shrubs can be purchased from your local NRD. The North Platte NRD charges $42.50 per 50 plants.

Costs for Installing a Drip Line

Constructing a drip line requires a nearby water source and the following items: 1 inch UV tubing, woodpecker drippers (0.5 GPH), 16 mm UV tubing plus a tubing holding stake (Figure 1). (Product source:  www.hummert.com/catalog.aspx) The estimated cost for 100 feet of drip line with trees spaced every 10 feet would be $32. One hundred feet of landscape fabric would cost $55 plus ground staples placed every 4 feet to hold the fabric in place $3 and ten Protex tube tree protectors at $4. The cost to install 100 feet of drip line plus landscape fabric and tree protectors would be $94 or $9.40 per tree spaced every 10 feet. This investment would increase tree survival to 91% three months after planting compared to 84% with herbicide for weed control and hand watering. The labor to plant trees, fabricate the drip line, and install landscape fabric was estimated at 12 minutes per tree per person.

Robert Wilson
Extension Weed Specialist