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Garden Clippings 2017 Vol. 36:2

April 1

A monthly e-newsletter from UMass Extension, published March to October, for home gardeners.

To read the articles in each section of the newsletter, click on the section headings below to expand the content:

Tips of the Month

April is the Month to…..

  • Monitor for winter moth caterpillars. Winter moth caterpillars cause damage to many different deciduous plants such as oaks, maples, cherries, ash, crabapples, apples and blueberries, and are active primarily in eastern Massachusetts. Winter moth eggs typically hatch early-mid April, and the young larvae quickly start feeding on flower buds, leaf buds and young developing leaves. Winter moth egg hatch has not yet been observed for this growing season as of 4/5/17 in Massachusetts. Scouts are still reporting that winter moth eggs are orange in color and have not yet turned the blue color that indicates hatch is imminent. Once the blue color change is observed in eastern Massachusetts, look to UMass Extension's Landscape Message and our Landscape, Nursery, and Urban Forestry Facebook page @UMassExtLandscape for announcements indicating winter moth egg hatch has begun. Monitor expanding buds and developing leaves for winter moth caterpillars on susceptible trees and manage early, if needed. Go to for our factsheet with more info on managing winter moth.

  • Divide herbaceous perennials. The ideal time to divide most perennials is early spring when the plants are dormant and less subject to shock. Spring divisions also have the entire season to recover from the stress of division. Before dividing, take time to prepare a new site for your newly divided plants. Start by digging around the plant, then lift the entire clump out of the ground. Using a spade or sharp knife, cut the clump into separate pieces. Discard the old, dead center and trim off any damaged roots. Keep the divisions moist and shaded while you prepare a new site for replanting. After replanting, keep transplants well watered.

  • Prune summer flowering shrubs. Early April is a good time to prune summer flowering shrubs such big leaf hydrangea, panicle hydrangea, butterfly bush, buttonbush, summersweet, clethra, sweetspire, and summer flowering spirea, since these shrubs form their flower buds on the current season’s stem growth. Pruning these plants in winter or early spring leads to vigorous stem growth in the spring and summer that contains buds which will flower in the summer and early fall.

  • Prepare garden soil for planting. Do not work your soil when it is wet. Tilling or digging when the soil is wet will cause it to dry into hard clods. Wait to prepare soil until it is dry enough. To test if your soil is dry enough, take a handful of soil and squeeze it. If the soil crumbles easily when you open your hand, it is ready to be tilled. If it does not crumble, it is too wet. Allow the soil to dry for a few more days and test again before digging. Before planting is also a good time to get a Routine Soil Analysis from the UMass Soil and Plant Nutrient Testing Lab to check pH and fertility. This economical soil test will provide recommendations for liming and fertilizing as needed, as well as indicating the lead level in the soil.

  • Plant pansies and other cold tolerant flowers such as petunia and snapdragon. As these plants become available at local garden centers, prepare your garden for planting. Place where they will receive full sun, although some pansies may tolerate partial shade. Water plants thoroughly after planting and mulch lightly with organic mulch if possible.

  • Start a vegetable garden. It is a good time to sow seeds of cool season crops such as lettuce, chard, kale, arugula, spinach, carrot, radish, beet and turnips. Plant the seeds as soon as the ground can be worked. Crops such as spinach, beets, radish, carrots and lettuce are sowed thickly in rows and thinned later to the desired stand and to allow them to develop properly. Root crops such as carrots, beets, and radishes should be thinned to a 2-inch spacing to allow the roots to develop properly. They can be thinned as soon as they reach small edible size. 

  • Rake the lawn to remove dead grass and other debris. To facilitate quicker regrowth, rake the turf lightly with a leaf rake. Do not use a garden rake as it will damage the turf. Raking will remove dead and blighted blades and other debris, will facilitate recovery from snow mold, and promote quicker regrowth. 

  • Celebrate Arbor Day by planting a tree on April 28. Generally the last Friday in April, Arbor Day is an annual observance that celebrates the role of trees in our lives and promotes tree planting and care.

Geoffrey Njue, UMass Extension Specialist

Timely Topics

How can I make my landscape more resistant to tree and shrub diseases? 

Many plant pathogens are either host specific or attack a narrow range of closely-related plants. Therefore, increasing diversity can help to create a disease resistant landscape. If a landscape is dominated by a single plant species (e.g. boxwood), its associated diseases can readily spread and large volumes of inoculum (diseased plant material that harbors the pathogen and allows it to spread and persist on the site) can develop. By increasing diversity and thereby reducing the total number of any particular plant species, you decrease the risk of losing many plants to a single disease and ensure that large amounts of inoculum cannot develop.

Focus on plants that are adapted to your particular site. For example, if your landscape is heavily shaded, avoid planting trees and shrubs that require full sun. A lack of sufficient sunlight is a major predisposing stress for certain trees and shrubs (e.g. white pine and Douglas-fir). Conversely, if your landscape is windy and sunny, choose plants that are tolerant of drought and thrive in full sun, exposed settings. The drought of 2016 is a good reminder that creating stress resistant landscapes can help to avoid significant losses in expensive plant material.  

Nicholas J. Brazee, UMass Extension Plant Pathologist

News for Gardeners

Plant Water Use and the Impact of Drought

All areas of Massachusetts experienced some level of drought in 2016. Although the timing and severity may have differed, many plant responses were similar. To understand why plants have certain responses to water stress and to predict longer term impacts of drought, it is important to consider some of the ways plants use water.  

Plants use water in four main ways including transpiration, transport of mineral nutrients, metabolic processes, and for turgor pressure. Transpiration is the evaporation of water from plants to the atmosphere. It is the process by which plants are cooled and is dependent on humidity. Lower humidity and higher temperatures increase the rate of transpiration. Mineral nutrients from the soil are dissolved in water and move from the roots through the xylem to the leaves where they are utilized in processes such as photosynthesis. Water is also needed for photosynthesis, as well as other metabolic reactions. The production of carbohydrates, proteins, plant hormones, and secondary metabolites can all be disrupted by water stress. Turgor pressure provides structure and is needed for cell elongation. Turgor pressure is needed for non-woody plants to remain upright. 

Most horticultural plants have mechanisms that are utilized or developed in order to retain or obtain water during drought. These mechanisms can be plant traits that are present before drought stress occurs such as deep root systems, growing in an ecological niche, or leaf features. Deep root systems allow plants to have access to water over a greater area of the soil profile. Some plants grow in areas where drought is unlikely or may be an ecotype that is more tolerant of drought. Leaf features that help with drought include thick, fleshy stems and leaves that can store water, waxy coated leaves that help to reduce transpiration, hairy leaves that help to reduce wind movement around leaves (reducing transpiration), light colored foliage (silver, gray, blue, white) which reflects light (reducing heating), and narrow leaves, which reduces the surface area for heating. 

Other mechanisms are in response to drought. Plants close their stomata (tiny openings in the leaf undersides, through which gases and water vapor pass) in response to soil drying in order to decrease transpiration. Leaf movements, including rolling, wilting, and changing orientation, can reduce heating of leaf surfaces via light and/or limit transpiration. Rolling leaves reduces the leaf areas exposed to light (therefore heating), reduces area movement along the leaf surface, and creates a high humidity environment within the roll which reduces transpiration. In some cases, plants may even drop some or all of their leaves to reduce transpiration.

Short term drought symptoms can include marginal leaf scorch, rolled or folded leaves, leaf drop, early fall color, wilting, off-colored or yellow leaves, twig and branch dieback, and reduced growth. These symptoms can be the result of reduced water for transpiration, nutrient deficiencies due to reduced transport, and/or reduced photosynthesis. Reduced photosynthesis can be the result of fewer leaves, closed stomata, or changes in leaf orientation. Over long periods of time, this can lead to reduced growth and reduced carbohydrate production and storage.

Moving into 2017, the extent of continued damage will be variable depending on type of plant, extent of establishment, type of soil, the area the plant is located, and how long the drought continues. There is a greater likelihood of damage with new plants, plants with smaller root systems, plants with shallow root systems, plants with injuries, or plants with poor or damaged root systems. 

Damage caused by water stress in 2016 may become evident in ways other than drought stress symptoms. During the winter, drought stressed plants will be more likely to have weakened branches break during storms. Drought stressed plants are also more susceptible to typical winter injuries including desiccation (especially broadleaved evergreens), sunscald, frost splitting, winter burn, or dieback. Stressed plants are also more likely to have increased injury from de-icing salts as high concentrations of de-icing salts can cause additional drought stress. 

It can be challenging to identify symptoms of drought stress, as many of the symptoms can be similar to those of other stressors such as nutrient deficiencies or diseases. In general, injury from drought stress usually occurs from the top of plant down and the outside in. For evergreens, needle browning occurs from the tip downward. Other symptoms can include fewer and/or smaller leaves, shorter branches, fewer flowers and/or fruit, loss of branches, heavy seed loads, and dieback.

Root hairs and feeder roots which are generally located in the upper foot of soil are usually the first to die during drought. These are the roots that take up the greatest amounts of water and nutrients, so, even as the drought lessens, plants can still have reduced water and nutrient uptake, as it can take years for root systems to be repaired. This can lead to nutrient deficiencies even when nutrients are present in the soil.

Drought-weakened plants have increased susceptibility to insects and diseases. Disruption of metabolic processes also means that that the production of protective chemicals by the plant is reduced. Plants, especially plants with physical damage such as cracks in branches, should be monitored. Root rots, cankers, wood rots, spider mites, and wood boring insects are more likely to occur in response to drought stress. 

Moving Forward….
In developing new landscapes or maintaining existing landscapes, it is important to consider water conservation principles in design, installation, and maintenance to help promote more sustainable landscapes. 

Design with irrigation and plant water needs in mind.

  • Group plants by water needs and to allow for reduced and efficient irrigation practices.

Improve or maintain soil structure to promote water conservation.

When irrigation is possible, make sure it's efficient.

  • Use drip irrigation or soaker hoses.
  • Maintain irrigation systems to avoid water loss and improve application efficiency and uniformity.
  • Adjust applications according to environmental conditions and changing plant water needs.
  • Plants need around 1” of water per week, applied slowly to a depth of 8-12”. Frequency and duration will depend on soil and weather.
  • Remember plants need 2-3 years for establishment.

Mulch to reduce evaporation from the soil.

  • Apply a 2-4” layer, kept away from the trunk/base of plant.
  • Helps control fluctuating soil temperatures.
  • Adds organic matter to the soil.
  • Helps reduce weeds.

Choose the right plant for the right place (including turf)

  • Group plants to help improve irrigation efficiency.

Appropriate maintenance

  • Avoid over-fertilization, as it increases growth which increases the water demand of the plant.
  • Control weeds to reduce water competition.
  • Only prune damaged or dead branches to avoid increasing the amount of stress on the plant.

Remember that drought stress symptoms can be delayed as plants use up stored carbohydrates and that the effects of severe drought stress can take years for recovery. Help reduce other stresses as plants recover. 

Caldwell, Ainsley. Drought and Urban Trees. City of Atlanta Department of Planning & Community Development. 2017, 2/13.
Douglas, Sharon. 2002. Minimizing the Long-Term Effects of Drought on Trees and Shrubs. The Connecticut Agricultural Experiment Station.
Hopkins and Hüner. 2004. Introduction to Plant Physiology.3rd Edition.  John Wiley & Sons Inc., Hoboken, NJ. 
Kujawski, Ron. 2011. Long-term Drought Effects on Trees and Shrubs. UMass Extension.
Seymour, R. M. and G. L. Wade. Make Every Drop Count: Xeriscape- Seven Steps to a Water-Wise Landscape. University of Georgia Extension. 

Mandy Bayer, Extension Assistant Professor of Sustainable Landscape Horticulture, University of Massachusetts Amherst

Trouble Maker of the Month

Be on the Lookout for Chili Thrips

The presence of the non-native, exotic chilli thrips (Scirtothrips dorsalis) has been recently been confirmed from two samples of damaged Hydrangea spp. foliage taken from two residential landscapes located in Barnstable County, MA and submitted to the UMass Plant Diagnostic Laboratory. At this time, this pest has not been detected in nurseries or greenhouses in Massachusetts or on any other host plants. Due to the limited number of samples, the significance of chilli thrips in Massachusetts is not known at this time.

This species of thrips is a significant global pest of economically important ornamental, vegetable, and fruit crops in southern and eastern Asia, Oceania, and parts of Africa. It was first determined to be established in the United States in 2005 in Florida, although previous interceptions of this pest were detected. It is reportedly a pest of over 100 host plants belonging to over 40 plant families, including, but not limited to, pepper, strawberry, blueberry, cotton, rose, peanut, Japanese privet, Rhododendron spp., Viburnum spp., eggplant, grapes, melon, tobacco, and tomato.

For more information, please visit our Chilli Thrips Fact Sheet at

Tawny Simisky, UMass Extension Entomologist

Plant of the Month

Magnolia x loebneri ‘Leonard Messel’

It seems fitting, seeing as the last Friday in April is Arbor Day, that the “Plant of the Month” for April should be a tree. The tree selected is Magnolia x loebneri ‘Leonard Messel’ or Leonard Messel magnolia, an elegant spring-blooming magnolia.

Named after Colonel Leonard Messel, the Leonard Messel magnolia is a chance hybrid found and raised at the Messel family’s Nyman’s Gardens, Handcross, Sussex., England; it is a natural cross between Magnolia kobus and Magnolia stellata ‘Rosea’.

M. ‘Leonard Messel’ is a deciduous, medium-size tree, slowly growing to a height of 15 - 25 feet, with an equal spread. It can be grown as a single trunk or as a multi-stemmed clump, and is often used as a specimen tree in a landscape. This is a tree for all seasons. The silvery-grey, slightly furry-looking buds, and silver-grey bark add winter interest to the landscape. The silvery bud scales open in mid-late April to deep fuchsia-pink buds that open to beautiful, fragrant 4 - 6 inch wide flowers, comprised of 12 - 15 fuchsia-pink ribbon or strap-like tepals (petals); white on the inside. The ribbon-like tepals move nicely in the wind, catching the sunlight, adding texture and movement in the garden. Another attribute for this magnificent magnolia is that the flowers are more frost resistant than star magnolia (Magnolia stellata) and saucer magnolia (Magnolia x soulangeana). Additionally, M. ‘Leonard Messel’ produces colorful yellow fall foliage, adding interest in the autumn landscape. Magnolia x loebneri ‘Leonard Messel’ is a sustainable tree, with no significant insect or disease problems, and adds color and interest in multiple seasons.

Hardy to zone 4, this plant grows best in full sun to very light, dappled shade and in a well-drained organic, slightly acidic soil. Watering during a prolonged drought is recommended.

Magnolia x loebneri ‘Leonard Messel’ has been the recipient of numerous plant awards including:

  • Cary Award, Tower Hill Botanical Garden, Boylston, MA
  • Kentucky’s Theodore Klein Plant Award
  • Award of Garden Merit - Royal Horticultural Society

Magnolia x loebneri 'Leonard Messel' bud Flowers of Magnolia × loebneri 'Leonard Messel' at Burcina Park, Biella, Italy Magnolia × loebneri 'Leonard Messel' in bloom

Deborah C. Swanson, Horticulturist

Upcoming Events

Each year, UMass Extension offers a workshop series for home gardeners and small scale farmers.

Remaining 2017 Topics are:

  • April 8         Home Orchard Establishment & Basics - a Hands-on Workshop (Sherborn)
  • April 15       Edible Landscaping with Fruit (Amherst)

For complete details, cost, and to register, go to

The Origins of New Shade and Ornamental Trees: The Roles of Serendipity and Breeding 
Dr. Michael Dirr

April 21 - 2:00 to 3:00 pm
UMass Amherst Design Building

​Dr. Michael Dirr is considered one of horticulture’s most celebrated plant experts. His Manual of Woody Landscape Plants: Their Identification, Ornamental Characteristics, Culture and Propagation and Uses is widely considered “the” reference text on the subject. This talk is part of the UMass Earth Day & Arbor Day Celebration with Dr. Michael Dirr. Proceeds to benefit UMass Extension and the UMass Waugh Arboretum.

For more details and to register, go to

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Diagnostic Services

The UMass Extension Plant Diagnostic Lab provides, for a fee, woody plant and turf disease analysis, woody plant and turf insect identification, turfgrass identification, weed identification, and offers a report of pest management strategies that are research based, economically sound and environmentally appropriate for the situation. Accurate diagnosis for a turf or landscape problem can often eliminate or reduce the need for pesticide use. Sampling procedures, detailed submission instructions and a list of fees.

The UMass Soil and Plant Nutrient Testing Laboratory at the University of Massachusetts Amherst provides test results and recommendations that lead to the wise and economical use of soils and soil amendments. The Routine Soil Analysis fits the needs of most home gardeners. Sampling procedures plus the different tests offered and a list of fees.

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