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Garden Clippings 2018 Vol. 37:2

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…..

  • Get back out into the yard! The time for spring cleaning has arrived and not just inside the house. April is a great time to begin tidying up the landscape and garden to prepare for the growing season. Trim back any remaining perennials and ornamental grasses before new growth begins. Edge beds and remove any debris to prep beds for spring planting. Make sure to avoid cultivating the soil when it is wet, as this is damaging to soil structure. Remove winter mulches from roses and other plants to prepare for the new season.
  • Test your soil. A soil test should be performed every three years to monitor soil pH and fertility levels, and will provide information on soil nutrient levels and fertilizer recommendations when needed. Keep in mind that, while fall is the best time for adding amendments to adjust soil pH, this can also be done in the spring, which is the time to address any fertility issues. A Routine Soil Analysis for $15 from the UMass Soil and Plant Nutrient Testing Lab will provide this information. Details at
  • Scout for winter damage. Look for any shallow rooted plants that may have experienced frost heaving and replant when the soil allows. Prune any broken branches that have not already been taken care of. Remember that some winter injury, such as salt spray damage, may not be evident until plants start to emerge from dormancy. It is also a good time to check if freeze-thaw events have disturbed paver patios or walkways. Out-of-place pavers can be re-positioned after temperatures are consistently above freezing. 
  • Start your lawn care. Lightly raking the lawn with a leaf rake will help to rejuvenate it from the winter. When Forsythia is in full bloom is a good time to apply pre-emergent crabgrass control. 
  • Mulch. Applying a fresh layer of mulch benefits the landscape in many ways. It is best to apply mulch before weeds germinate to aid in weed suppression. Other benefits include reducing evaporation from the soil and improving soil moisture, adding organic matter to the soil (with organic mulches), encouraging beneficial soil organisms, controlling erosion, and acting as an insulator for plant roots. Mulch should be applied 2-4 inches deep and should not be piled at the base of trees or shrubs. 
  • Know when and what to prune and divide. When pruning shrubs it is important to keep in mind when flower buds are developed; this is usually reflected in the blooming period. In general, shrubs that bloom in the spring set buds in late summer to early fall of the previous year; these shrubs should not be pruned until after they bloom in the spring. Summer and fall blooming shrubs develop buds in the spring and can be pruned in early spring before bud set. Spring is also a good time for pruning late summer and fall blooming perennials like coneflowers and aster. Spring and early summer flowering perennials should not be divided until fall. 
  • Be patient with spring bulb foliage. As spring bulbs start to decline, remember that it’s important not to cut back the foliage. After flowering, the plants continue to photosynthesize and are storing these food reserves in the bulb for next year. Removing spent flower stems is ok, but foliage should be left to allow for photosynthesis to continue. Foliage should be left until it naturally yellows and begins to die back. Planting annuals around bulbs is a great way to hide the remaining bulb foliage. Planting late spring and early summer perennials that begin to emerge as the bulbs fade is also a great method of hiding bulb foliage. 
  • Start your garden! Outdoors it’s time to sow cool season plants such as carrots, beets, and lettuces. Seeds can be sown or transplants planted when the ground can be worked (keeping in mind not to work the soil when wet). Warm season plants such as tomatoes can be started indoors. Indoors, supplemental lighting will likely be necessary to promote the best growth. 

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

Timely Topics

Soil Testing

Will this winter never end?! That’s what we want to know here at the UMass Soil & Plant Nutrient Testing Lab. Regardless of the weather, we are ready and eager to analyze your soil samples and right now the wait time is short before the rush begins. Visit our website at for sampling instructions, order forms, and a wealth of information about soil and soil testing. We look forward to helping you grow your best garden ever!

2018 Workshops for Home Gardeners

April 14 - Native Pollinator Biology and Conservation, Amherst

For more details, including how to register, go to

Defoliating Caterpillars: Outlook for 2018

Winter Moth
Monitoring for winter moth (Operophtera brumata) egg-hatch has begun. In fact, winter moth eggs are in such short supply in Massachusetts that our Landscape Message scouts are having a difficult to impossible time locating them to monitor their color change as the eggs develop. As of this week (4/4/18), Heather Faubert, with the University of Rhode Island, reports some winter moth egg color change at a single site in Rhode Island, but that less than 10% of the eggs are changing color and she believes them to be “outliers” or not truly representative of what is going on with the rest of the winter moth population. Eggs are tiny and green when first laid, but quickly turn a red-orange color soon after. At this time (early April), anyone monitoring winter moth eggs will most likely see that they are orange in color. As the egg develops, it will turn a bright blue color, shortly prior to egg hatch. Therefore, winter moth egg hatch has not yet begun (as of 4/4/18). Check the UMass Extension Landscape Message for updates.

Winter moths overwinter in the egg stage, hidden in cracks and crevices of host plant bark or beneath lichen. Eggs are tiny and very difficult to see. Egg hatch has historically occurred any time between late March to early-mid April, depending upon the year and the location. 

What can we expect from the winter moth population in eastern Massachusetts this year? Hopefully it will continue to be the lowest it has been in over a decade, as was seen in the 2017 season. Anyone with high-value crops that could be impacted by this pest should continue their normal monitoring activities to aid in decision-making regarding management of winter moth. Homeowners who experienced record-low winter moth populations last season may continue to enjoy such conditions again in 2018. For more information about the recent declines in the winter moth population, see the February issue of Hort Notes, under “Trouble Maker of the Month” at

Gypsy Moth
What can we expect from gypsy moth (Lymantria dispar) following the 2017 growing season, during which time caterpillars of this species defoliated over 923,000 acres across Massachusetts? (For a map of the 2017 defoliation due to gypsy moth, go to This may depend upon how many overwintering egg masses are visible near you. White oak is a preferred host for the caterpillar stage of this insect, but the host list for gypsy moth is very large, including the leaves of many deciduous trees and shrubs such as maple, birch, poplar, willow, apple, hawthorn, and many others. In years where heavy populations exist, such as in 2017, eastern white pine and spruce needles are also fed upon. 

The outlook for 2018 is undoubtedly much better than it would have been if the gypsy moth caterpillar-killing fungus, Entomophaga maimaiga, did not catch up with the caterpillars in late June of 2017. At that time, many dead caterpillars were seen hanging from tree trunks and branches, killed by the fungus, which was aided by the wet spring weather earlier in the year.

Despite the fungal outbreak sweeping through the caterpillar population, some lucky caterpillars survived to pupate and emerge as adult moths, mate and lay the egg masses that are currently overwintering. Generally, these are expected to hatch approximately the first week in May in Massachusetts, though the timing may vary depending upon local temperatures.

While it is very difficult to predict how much defoliation Massachusetts will see in 2018 due to gypsy moth caterpillar feeding, we can be certain that in areas where many egg masses are currently seen overwintering, pockets of defoliation could still occur across the state this year. Thanks to the gypsy moth caterpillar-killing fungus, the population should be on the decline, but we cannot expect the caterpillars to disappear completely from Massachusetts landscapes this season.  

Tawny Simisky, UMass Extension Entomologist

News for Gardeners

Timing of Spring Lawn Fertilization

Evolving nutrient management regulations in Massachusetts and beyond have brought increased focus on lawn fertilizer applications. A good lawn fertility schedule should seek to align maximum nutrient availability with periods of peak turfgrass growth. In the spring, the window of ideal growing conditions is relatively short – sandwiched between the recession of winter and subsequent grass recovery, and the arrival of hotter, drier conditions that bring summer-related stress to lawns along with associated growth and management challenges.

While it has been a cold and snowy spring thus far, Marathon Monday is less than a week away in Massachusetts, The Masters golf tournament just wrapped, and the fertilizer ads are heavy on the radio and TV. These influences always seem to motivate folks to jump on that first spring fertilizer application, and indeed, spreaders have been observed in action already.

After the average New England winter, time is one thing that a lawn needs after the snow melts and the soil begins to thaw. From a nutrient perspective, water must be unfrozen and in liquid form for nutrients to be mobile in soil and available for plant uptake. Fertilizer applied too early, when soil has not thawed completely and/or turf density has not recovered sufficiently from winter shoot dieback, has a much greater potential of being carried out of and away from the lawn area with runoff.

Roots also need to be active and viable for nutrient absorption to occur. Harsh winter conditions also cause roots to die back, therefore a degree of root system recovery should take place prior to fertilizer application. The physical passage of mineral nutrients from the soil into root tissue, furthermore, is a largely active process for which energy is required. This means that photosynthesis and other biological functions must be up and running to adequately supply this energy. Nutrients in the soil solution that are not taken up promptly may be subject to loss through leaching and runoff during rain events.

The start of spring growth...The simple solution to promote robust plant uptake and minimize nutrient loss is to wait to fertilize in the spring until growth is solidly established, with the minimum threshold being the point of approximately 50% green-up. Contrary to what some believe, fertilizing early will not stimulate earlier growth; the onset and acceleration of both shoot and root growth are largely temperature dependent. Also, the calendar is never really useful in this regard, because of often significant year-to-year variation. Further variation can be introduced by many factors including geography, air temperatures, soil temperatures, soil moisture levels, exposure, etc. While sunny sites in southeastern MA may be about ready, for example, sheltered locations in the Berkshires may need significantly more time. The progression of above-ground shoot growth and green color (see photo above left) are built-in signals that account for all of the above factors.

It is important to remember and keep in perspective that the aim is to maximize plant uptake while simultaneously minimizing nutrient loss from the system. Nutrients lost to the environment, most notably nitrogen and phosphorus, have a much greater potential of reaching and accumulating in ground and surface waters and negatively impacting the environment. In addition, nutrient loss is wasteful of time, labor, fertilizer, and money. Nutrients that leave the system will not support the desired response in the lawn, and may lead to performance problems and increase the need for future management attention.

For a final, related tip, don't let fertilizer/pest control combination products be the boss when it comes to application timing. While the intent of combination products is to 'kill two birds with one stone' for the sake of efficiency and convenience (fertilizer and pre-emergence herbicide, for example), the timing for one objective may have to be compromised in support of getting the correct timing for the other objective. If the compromise will be significant, opt for separate fertilizer and pest control applications for greater accuracy and control.

Jason D. Lanier, UMass Extension Turf Specialist

Trouble Maker of the Month

Verticillium Wilt: Get to Know this Destructive Landscape Disease

Verticillium wilt is one of the destructive diseases of ornamental trees in the landscape, but confirmation of the pathogen can be very difficult. The disease is caused by two species, Verticillium dahliae and V. albo-atrum. However, V. dahliae is responsible for the majority of infections on woody ornamentals in southern New England. A wide variety of forest and landscape trees and shrubs are susceptible to Verticillium wilt, but the most common hosts in this region include: maple (Acer), elm (Ulmus), smoketree (Cotinus), ash (Fraxinus), tulip poplar (Liriodendron), Viburnum, redbud (Cercis), CatalpaMagnolia, Kentucky coffee tree (Gymnocladus dioicus) and Russian olive (Elaeagnus angustifolia).

Infections from Verticillium originate in the soil, when the fungus invades the root system of susceptible plants. Once the fungus becomes established in the vascular system, it is transported throughout the canopy. Verticillium also grows through the ray cells in the trunk to penetrate deep into the secondary xylem. Symptoms can appear rapidly after infection and the most commonly observed symptoms of Verticillium wilt include marginal leaf scorch, leaf wilting, vascular staining and branch dieback.

Because there is a disruption of water and mineral transport to the affected branches and leaves, the symptoms appear similar to those caused by root disease, abiotic root damage (e.g. severing, crushing or compaction), drought stress and stem/branch cankering. Acute foliar symptoms can range from wilting, drying, marginal/interveinal browning and premature shedding on a single branch or one side of the tree’s canopy. These symptoms can appear at any time during the growing season. In addition, there are chronic symptoms that resemble a tree in decline, such as stunted growth, marginal leaf scorch, undersized and sparse foliage, heavy seed production and branch dieback.

Signs of verticillium wiltThe vascular staining that results from the disease is the best diagnostic symptom that can be used to determine if additional testing to confirm the pathogen is necessary. However, keep in mind that staining is not always present on infected trees and shrubs. Vascular staining is often olive-green in color but may range from yellow to brown, depending on the host. Because of the pathogen’s ability to move through ray cells, staining may be present deep in the trunk in the xylem tissue and not in the outer vascular tissue just under the bark (where vascular staining caused by Dutch elm disease is often observed).

One of the most interesting features of Verticillium is its ability to produce microsclerotia. These are very small, black-colored resting structures that resemble a small seed. Once Verticillium has caused disease, microsclerotia are produced within a variety of dead plant parts, including roots, stems and leaves. They allow the pathogen to overwinter in dead plant tissues and when produced in the soil, allow the fungus to persist for many years at the site. When infected leaves and stems fall to the ground, the fungus can also grow into the soil to overwinter. Contact between neighboring, healthy roots and dead, diseased roots can allow Verticillium to spread locally. Overland spread can occur when infected leaves are dispersed away from an infected tree by wind. In addition, Verticillium can infect several resistant weedy plants and create new microsclerotia without ever causing any above-ground symptoms. Therefore, once the fungus is established at a site, it can remain there indefinitely.

Verticillium is widespread in forest and landscape settings, yet disease incidence remains relatively low in most cases, signifying that many plants are able to resist the pathogen when attacked. The impact of Verticillium wilt depends on the inherent susceptibility of the tree/shrub, environmental stress (especially drought and root damage) and the virulence of the pathogen. Maintaining high tree vigor is essential, since the tree’s natural defense response may be able to compartmentalize the infection. For recently transplanted trees and shrubs, provide regular irrigation during extended dry periods, fertilize as needed and maintain an adequate mulch layer over as much of the root zone as possible. These activities do not have direct impacts on the pathogen itself, but they serve to enhance the tree's ability to resist infections.

Reduce inoculum and improve the appearance of infected trees and shrubs by removing dead shoots and branches. Keep in mind, however, that pruning does not eliminate Verticillium from the plant since infections first establish from the roots. Because of the soilborne nature of the fungus and its establishment within the roots, fungicides often have little to no effect. Use of resistant or immune trees and shrubs as replacement for those infected with Verticillium wilt is often the only viable strategy in landscape settings. A selected list of resistant trees and shrubs include: apple/crabapple (Malus), beech (Fagus), birch (Betula), boxwood (Buxus), dogwood (Cornus), hackberry (Celtis), hawthorn (Crataegus), hickory (Carya), holly (Ilex), honeylocust (Gleditsia triacanthos), katsura (Cercidiphyllum), linden (Tilia), mountain-ash (Sorbus), oak (Quercus), pear (Pyrus), aspen/poplar (Populus), sycamore/planetree (Platanus), sweetgum (Liquidambar) and walnut (Juglans). All conifers are also resistant or immune to Verticillium wilt. Resistance does not imply immunity; therefore some of the plants listed here may be susceptible to infection.

Nicholas J. Brazee, UMass Extension Plant Pathologist

Plant of the Month

Magnolia x soulangeana, Saucer Magnolia

Saucer magnolia is a small deciduous tree growing about 20-25 feet tall and 20-25 feet wide.  Fragrant, large white to purplish flowers appear in April.  Saucer magnolia is hardy in USDA zones 4-9, prefers moist, acidic, well-drained soils and grows best in full sun to part shade.

The tree is a hybrid resulting from the cross of Magnolia denudata x Magnolia liliiflora.  The original cross was made in France in the early 1800s.  M. denudata is a pyramidal 30-40 foot tree with white flowers and M. liliiflora is an 8-12 foot shrub with purplish rose colored flowers. The resulting hybrid combines the characteristics of both parents, giving M. x soulangeana a larger size but often a multi-stemmed habit like a shrub, with flowers that range from pure white to purple, often containing a mixture of both colors. The hybrid quickly became popular and is one of the most commonly planted deciduous magnolias.  

The tree is typically upright in youth, then becoming wide over time.  Older specimens often have a very pleasing spreading habit with large, drooping lower branches.  The drooping lower branches, smooth gray bark, and large fuzzy terminal flower buds provide winter interest. The large, 5-9 inch flowers are what makes it so garden worthy.  Leaves are 3-6 inches long and are a dark green that remains attractive all summer long.

The tree is tolerant of all soil textures and is adaptable, but prefers a moist, rich, high organic matter soil.  Saucer magnolia is not suitable for harsh sites or urban plantings.  In the landscape, it is best suited as a specimen small flowering tree. The tree does have a few liabilities, the primary one being frost damage to the flowers while in bloom, which happens occasionally but not as much as with star magnolia, Magnolia stellata.  Saucer magnolia is also a host for several scale insects and leaf spots; however, neither seem to be common problems.

Well known hardy cultivars include:

‘Alexandrina’ – flowers purple outside, white inside

‘Amabilis’ – flowers large cream color, some pink at base

‘Brozzonii’ – white flowers with some purple at base, flowers later than others

‘Verbanica’ – purplish/rose flowers, flowers with ‘Brozzonii’




Russ Norton, Agriculture & Horticulture Extension Educator, Cape Cod Cooperative Extension

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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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