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Identifying Low-Maintenance Hydrangeas

If you drove or walked the three-mile drive at the Minnesota Landscape Arboretum during late summer or fall in 2013, chances are you stopped for a visit at the Earth-Kind® hydrangea trial. Planted in the fall of 2010, this planting exploded with growth and bloom last year and it was hard to resist stopping for a walk through the beds.

K Zuzek, UMN Extension

Photo 1: Locations of the 5 Earth-Kind Hydrangea trials

The hydrangea planting at the arboretum is one of five Earth-Kind® plantings in the Upper Midwest (Photo 1) that are being used to provide information on the performance of 24 hydrangeas being grown under low input maintenance conditions. The Earth-Kind® program was started in the early 1990's by Dr. Steven George at Texas Agrilife Extension Service to promote environmentally responsible landscape management practices that address diminishing water resources, the overuse and misuse of fertilizers and pesticides, and poor soil health that can diminish plant health. Earth-Kind® landscape practices include minimizing irrigation, providing fertility and improving soil health through the use of compost and organic mulches rather than fertilizers, the reduced use of pesticides, and the identification of genetically strong cultivars and species that will perform well under these low input conditions. The hydrangea trial sites are being used both to identify these strong cultivars and as outdoor classrooms to educate the public on environmentally friendly landscape management.

K Zuzek, UMN Extension

Photo 2: Plot preparation at the MLA

Cultivar trial establishment involves creating 4 blocks (planting beds) at each trial site. Each of the 24 cultivars being trialed is planted once in each of the 4 blocks in a randomized design. This means that 4 plants of each cultivar are planted at each site and their location is different within each of the 4 blocks. Four plants at each of the 5 sites provide us with 20 plants of each cultivar to focus our evaluation efforts on. This replication and randomization gives us statistically strong evaluation data to draw conclusions from. Plot establishment includes eliminating native vegetation (this is the one of the few times an herbicide is used) (Photo 2), incorporating 3" of compost into the native soil, planting, and applying 3" of organic mulch (usually wood chips) (Photo 3). Plants receive consistent irrigation as they establish during year 1.

K Zuzek, UMN Extension

Photo 3: Wood chipping during plot establishment

During years 2-4, irrigation is minimized and watering occurs only if plants wilt during periods of severe drought. Throughout the 4 year study, herbicides are applied only to control invasive weeds such as Canadian thistle if they appear in the plots. The 3" mulch layer minimizes weed establishment and weeds that do appear in the plots are removed by hand weeding. No fertilizers are applied. Organic mulch is reapplied as needed to maintain a 3" depth.

K Zuzek, UMN Extension

Photo 4: MLA plots in year 2 (July 2012)

During years 2-4, evaluation data is collected monthly on the 96 plants at each site. Data is collected on floral and foliar quality, plant size and habit, tolerance to environmental stresses (cold hardiness, drought tolerance, high soil pH, etc.), disease and insect tolerance, and the ability to perform well across a wide variety of soil conditions. Superior hydrangea cultivars that perform well across years and trial sites will be designated as Earth-Kind plants for their region so that gardeners and horticultural professionals know that these cultivars perform well with basic plant care.

K Zuzek, UMN Extension

Photo 5: MLA plots in year 3 (July 2013)

Twenty-four hydrangea cultivars were planted in the trial. Fourteen of the cultivars are panicle hydrangeas (Hydrangea paniculata) and include First Editions® Great Star, First Editions® Tickled Pink®, First Editions® Vanilla Strawberry™, First Editions® White Diamonds®, 'Grandiflora' (also known as PeeGee), 'Limelight', 'Little Lamb', Little Lime™, 'PeeGee Compact', 'Pink Diamond', Pinky Winky™, Quick Fire®, 'Tardiva', and 'Unique'. Seven of the cultivars are smooth hydrangeas (H. arborescens) and include 'Anabelle', 'Bounty', Endless Summer® Bella Anna®, 'Hayes Starburst', Incrediball®, Invincibelle® Spirit and White Dome®. The remaining three cultivars are bigleaf hydrangeas (H. macrophylla) and include Endless Summer® Blushing Bride, Endless Summer® The Original, and Endless Summer® Twist-n-Shout®.

The Benefits of Earth-Kind®
Low input gardening and the identification of plant cultivars that thrive with minimal maintenance benefit gardeners and the environment. The use of genetically strong and well-adapted plants makes it much easier and more enjoyable for gardeners and landscapers to create and maintain beautiful landscapes. There is also a large reduction in labor and the cost of maintenance. Few plants need replacing if adapted and pest-tolerant cultivars are selected for use in a landscape. The use of these tolerant cultivars minimizes the amount of irrigation needed and the use of pesticides. Replenishing organic mulches can be labor intensive but the benefits to gardeners and plants far outweigh the added labor. Mulch provides weed control, reduces the need for irrigation by decreasing evaporation of water from soil, and buffers soil temperature to protect roots during the intense cold of winter and the heat of the growing season. As it decomposes mulch improves soil structure and creates healthier root environments for garden plants: nutrient- and water-holding capacity increase in sandy soils and soil porosity, water infiltration and drainage, oxygen levels, and root penetration improve in heavier clay soils. The health and appearance of plants improves as soil quality improves. Improved soil texture also goes a long way towards making the job of hand weeding a much easier task for gardeners.

As individuals, the impact of our landscape management practices on the environment may be very small but collectively we have an enormous and sometimes a negative impact. As we change our gardening practices, we can reduce or eliminate these negative impacts. Fertilizers and pesticides have the potential to decrease water quality if they move over impervious surfaces such as driveways and sidewalks and into our streams, rivers and lakes through storm sewer systems. As the use of these chemicals is reduced, so is the potential for them to reach the water bodies that we treasure so much in Minnesota. The use of water-wise practices such as drip irrigation and the selection of drought-tolerant plants help to conserve water resources in a time when climate change is creating longer and more frequent periods of drought that put additional demands on these diminishing water resources. The use of organic mulches improves soil quality and reduces the amount of yard waste entering landfills.

The benefits of low input landscape management practices have been documented in Texas where the Earth-Kind® program has been in existence for over 20 years. In gardens or communities where Earth-Kind® landscape management practices are practiced, there have been 50-70% water savings, a 98% reduction in the use of pesticides, and a 20% reduction of yard waste entering landfills. In Addison, TX where the parks & recreation department uses Earth-Kind® management, there was a 50% reduction in labor costs due to the reduced need for irrigation, weeding, fertilizers and pesticides, and replanting. The department saw a 70% reduction in water usage and lost the dubious honor of being the town's largest water consumer.

The effectiveness of the Earth-Kind® plant evaluation effort can also be seen in Texas. To date, 23 roses have been designated as Earth-Kind roses for the southern United States. These plants have high tolerances to pests and perform beautifully under harsh summer temperatures and drought conditions such as those seen in 2011 when Dallas set records for the most 100 degree days, highest daytime and night temperatures, and drought (3.6" of rainfall from March to August instead of the average 17").
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