Fall is for Planting...Boxwood!

By Holly Scoggins and J. Bennett Saunders

The cooler, wetter months of autumn are an ideal time for planting woody ornamentals and herbaceous perennials, especially boxwood (Buxus species and cultivars). Let’s review some cultivar selection tips and best practices for design, planting, and aftercare. 

Boxwood, historically the aristocrat of shrubs, remains a popular choice for more formal landscapes. Though substitutes are touted, nothing tops the lush evergreen foliage, shape-ability, and that irreplaceable quality of deer-resistance of boxwood.  

The quiet sophistication of boxwood in a formal garden is unmatched, and best management practices will help keep them healthy and beautiful. (photo courtesy of Tom Belden, John Richmond Landscaping, Inc.)

Boxwood do have a few important pests and pathogens. Regarding pests, boxwood leafminer (Monarthropalpus flavus) is an issue across much of the United States. Box tree moth (Cydalima perspectalis) has made its way to North America. Boxwood blight Calonectria pseudonaviculata is taking its toll on boxwood in eastern North America as well the West Coast. The fungal disease thrives with mild temperatures (60°-77°F) and wet conditions and can survive for years in infected plant debris. However, there are several keys to optimizing boxwood health in the landscape and reducing the chance of boxwood diseases and pests —cultivar selection, attentiveness to mature size/spacing and site selection.

Which Boxwood?

Success starts with plant selection. No boxwood variety can claim complete resistance to both boxwood blight and boxwood leafminer, but research trials and field experience with more than 130 varieties reveal some common-sense selections.  To cross off the list: Buxus sempervirens ‘Suffruticosa’ (European or English Boxwood) - a “plant of the past” that is highly susceptible to boxwood blight - many good alternatives exist.  Buxus sempervirens (American Boxwood) cultivars vary in their landscape performance and degree of blight and leafminer resistance. However, Buxus microphylla varieties topped resistance rating and are thus a good choice for blight-prone areas that also experience leafminer.  The cold-hardy Buxus sinica var. insularis  hybrids such as ‘Green Velvet’ show some resistance to boxwood blight but susceptibility to boxwood leafminer. A terrific source of cultivar-specific information is the beloved “Boxwood Guide” published by Saunders Brothers Inc. and now in its 6th edition - PDF available for free - download at https://www.saundersbrothers.com/page/Boxwood-Guide

All cultivars listed below exhibit reasonable resistance to both boxwood blight and boxwood leafminer. 

·      Low hedges and other edging purposes call for dwarf cultivars, such as B. microphylla ‘Little Missy’ and B.sinica var. insularis ‘Nana’. Always confirm mature size of a cultivar.

·      For classic green orbs as specimens or foundation plants in the 3-to-5-foot range, consider NewGen Freedom® (Buxus ‘SB 300’ PP324421) or NewGen Independence®  (Buxus ‘SB 108’ PP28888),  both of B. microphylla heritage. Buxus microphylla var. japonica ‘Green Beauty’ is also a durable choice but may require leafminer management. When a gold variegated form is desired, B. microphylla Golden Dream (‘Peergold’PP16052) shows reasonable resistance to both issues. 

·      Upright boxwood are irreplaceable for vertical interest. Though a bit more susceptible to blight in trials, B.sempervirens cultivars ‘Dee Runk’ and ‘Fastigiata’ remain popular. When used for vertical interest, proper spacing and placing them in a location with good airflow can help mitigate boxwood blight.

Boxwood plays well with others! Orbs of boxwood NewGen Independence® and a hedge of ‘Little Missy’ compliment the sparkling summer blooms of Oakleaf hydrangea (Hydrangea quercifolia ‘Munchkin’). (Photo courtesy of Paul Westervelt, Saunders Brothers Inc.) 

Site Selection, Spacing, and Installation

When considering placement, note sun tolerance varies by cultivar. Afternoon shade is optimal.  Another siting consideration—high and dry(ish) if possible. Boxwood appreciate well-drained soil and will struggle with wet feet. Good drainage minimizes the chance for Phytophthora and other root zone diseases. 

As with any other landscape ornamentals, confirm cultivar-specific mature size when spacing to ensure long-term satisfaction with the project. What will the garden look like in 10 to 20 years?  

For a border or other row-type application, clipped hedges are perpetually popular, but consider the “pearl necklace” approach as well—generous spacing allows for air movement, a key to reducing the potential for blight. If utilizing boxwood for a foundation planting, ensure sufficient spacing away from the structure and place well away from downspouts to maximize air circulation and minimize potential for a wet rootzone.

When installing, pay particular attention to best planting practices. Planting the top of the root ball approximately 2 inches above ground level, a bit higher than the soil line, helps ensure proper drainage. 

Boxwood blight research has demonstrated that a light layer of mulch (one inch the first year, one-half inch per year thereafter) will reduce splashing of precipitation that might carry spores—boxwood blight spreads easily via mechanical/water movement. Overhead or other spray irrigation is discouraged for the same reason; drip irrigation is preferred. If hand-watering is required, direct your client to water the soil, not the foliage. Immediately after transplanting, water thoroughly again and continue to monitor moisture for 18 months or so, until the plant is established. Once severely drought-stressed, boxwood seldom recovers completely. 

Here’s an example of proper selection and spacing for optimal air movement with Buxus microphylla var. japonica ‘Jim Stauffer’. The light layer of mulch prevents water splash and lessens potential for the spread of boxwood blight.  (Photo courtesy of J. Bennett Saunders, Saunders Genetics, LLC). 

Transplant Tips

If a client has a beloved (and healthy) specimen boxwood that requires relocation, fall is the best time for transplant efforts. Some landscapers have success transplanting during mild winters, particularly in USDA Plant Hardiness Zones 7-9. Proper timing will allow for maximum root growth when moisture is typically more abundant. This in turn better prepares the plant for dry summers. 

Increase chances of success by adequately watering the plant prior to any digging. The root ball should be dug as wide as the canopy of the plant (at a minimum). The root ball size will vary but a rule of thumb should be for every one foot in width, the depth should be six inches. Since boxwood have shallow roots, greater focus should be on root ball width than depth. 

As with any transplant project, do not leave the boxwood above ground for a long period, especially in times of extreme heat or cold. Never allow the root ball to dry out. Never move boxwood during the stress of summer heat or severe drought.

Sourcing Plant Material

To conclude, here are a few final thoughts on sourcing. Departments of Agriculture for many states maintain a boxwood blight cleanliness program along with a compliance agreement for nurseries. These agreements describe comprehensive best management practices to be followed. Source boxwood material from nurseries listed! These nursery growers uphold the highest standards of sanitation and best practices to keep boxwood blight out of the supply chain.  

For in-depth resources and tips on boxwood care for both homeowners and landscape professionals, visit www.newgenboxwood.com.

A similar version of this article by Holly and Bennett appeared in the digital newsletter of the Association of Professional Landscape Designers, August 2021. https://issuu.com/designonline/docs/apld_design_online_august_2021

Frost or Freeze Damage and How to Manage It

Straw-colored foliage is typical of spring frost injury.

This year, 2020, is already in the history books as the “Year of the Coronavirus,” but boxwood growers will also remember it for some of the worst frost/freeze damage seen in decades. Central Virginia experienced two abnormally late spring frosts, one in mid-April and the other on Mother’s Day morning, May 10. Although boxwood are typically hardy evergreens that can tolerate cold, they can be susceptible to injury when extreme weather events occur. There are two different types of cold temperature-related issues. Abnormally cold night temperatures in the fall or spring result in frost or freeze damage whereas extreme cold winter temperature events result in cold injury.

Frost or Freeze Damage

Running irrigation water over the plants during a cold event can minimize frost or freeze injury.

The terminology frost damage usually refers to a rather mild frosting of plants in the fall or spring, generally resulting in light die-back in the tops of boxwood. Freeze damage occurs at the same time but describes more severe damage as a result of colder temperatures or more prolonged cold temperatures. In the mid-Atlantic area of the United States, the damage from these weather events can occur in the fall from October through early November, or in the spring from late March through early May. The resulting damage is a “burning” of the most tender foliage, usually the tips of the newest growth, of the boxwood. The damage occurs when the temperature gets below 30 degrees Fahrenheit, with the worst damage occurring during a freeze event when the temperatures get into the low to mid 20’s. An extreme freeze event, with temperatures in the low 20’s in the fall or spring, can cause bark splitting, with resulting dead limbs of perhaps even the entire plant.

Frost blankets are specifically designed to be placed over plants during cold weather events. The fabric is breathable to prevent diseases, but warm enough to protect tender boxwood.

The discoloration and spotting on this Buxus microphylla cultivar could be mistaken for Boxwood Blight but is actually a common sign of frost or freeze damage.

In the fall, the extent of the damage of a frost/freeze event is related to the temperatures leading up to the cold temperatures, with the worst damage occurring with a very warm fall followed quickly by a severe and early frost or freeze.

In the Spring, the extent of the damage is related to the development of the new growth in the boxwood, with the worst damage occurring with a very early and warm spring fully pushing out the new growth of the boxwood, followed by an abnormally cold night.

Feb. 2020: Third International Summit on Boxwood Challenges

The NewGen™ and Saunders Brothers teams at the Third International Summit on Boxwood Challenges, hosted by the American Boxwood Society.

Last month the American Boxwood Society hosted its Third International Summit on Current Boxwood Challenges. Over 140 people heard from researchers and growers from Europe, Canada and the United States who discussed the latest research on Boxwood Blight and the Boxwood Tree Moth. This one-day event was hosted at the National Agricultural Library in Beltsville, Maryland.

Although the Boxwood Tree Moth has not been found in the United States, it has devastated boxwood production in Europe. The morning session of the event began with research on the biology of the moth, determining the invasive pathways that introduced the moth to Europe, concluding that the pest was originally introduced from eastern China to Germany in 2007 and has since spread significantly over Europe. Most of the spread has been from the transport of infected plant material, with some movement through native boxwood forests. The moth was found in the United Kingdom in 2008 and has since spread around the southern parts of the country. Chris Poole, the Chairman of the European Boxwood & Topiary Society, shared management strategies being utilized in the United Kingdom and around Europe against the moth.

The morning session finished with speakers from North America, focusing on what the Canadian industry is doing to monitor and prevent the spread, and how the U.S. can prepare against the moth. First identified in Ontario in October 2018, OMAFRA (similar to U.S. Extension) has diligently been monitoring and treating the pest as it appears. Using many of the same tactics that have been effective in Europe, most infections are low to moderate, with less than 10% considered severe. In the United States, using pheromone traps for detection and diligently spreading the word about this potentially invasive species can aid in catching the moth early. In the event that it is found, there are methods of control already available. Researchers are aware of the pest and are focusing efforts to learn from those already affected in order to prevent the introduction of Boxwood Tree Moth to the United States.

The afternoon focused on Boxwood Blight starting with a recap of what is known about the disease and ways to treat and prevent it. Mary Ann Hansen, who works in the Plant Disease Clinic at Virginia Tech, has many years’ experience identifying Boxwood Blight. She shared information about the biology of the disease, how to identify it, and how to clean it up in the event of an infection. There are many tools available to the public about Boxwood Blight, including the Virginia Boxwood Blight Task force website.

The event finished with several presentations on further research being done around the U.S. There are many projects in the works focused on learning new and effective control strategies. Projects range from breeding programs to biocontrol studies to thermotherapy, all being done at many universities around the U.S. There is still no silver bullet in preventing or treating Boxwood Blight, but the is a light at the end of the tunnel as much of the research proves positive. One of the recent studies showed a decrease of Boxwood Blight lesions by 97% just from adding a layer of mulch. You can read more about that study here. As research continues, we only get more positive that as an industry we can overcome this challenge.

If you’d like to learn more about events like these, check out the American Boxwood Society’s website.

Tips and Tricks for Growing Cleaner Plants

Creating a phytosanitary plan doesn’t have to be a daunting endeavor. There are many simple steps you can take to grow cleaner plants. Saunders Brothers has worked with many researchers and Extension agents to establish protocol to help prevent the introduction and spread of Boxwood Blight at their nurseries. Although this plan was designed with Boxwood Blight in mind, these practices will help growers produce cleaner, more successful plants.

Foot mats/baths:

Foot baths are located at every walkway leading to the Saunders Brothers office.

One of the first and easiest steps to take is the inclusion of foot mats/baths for sterilizing shoes of anyone entering a growing area. These can be placed in greenhouses, worker common areas, and near offices. Having foot baths as a first line of defense minimizes the introduction of new pathogens to your growing area. Saunders Brothers uses foot mats at the entrance to all of their office and worker areas. Saunders Brothers uses Zerotol® 2.0, but a 10% bleach solution is also effective.

Disposable pant/boot covers:

Crews in the field nursery wear disposable suits when they are working on larger plants.

Crews wear rubber boots that can be easily cleaned and disposable pants when moving between growing areas.

An example of plastic pant and boot covers in the field.

Disposable pants and boots serve as a physical barrier between one’s clothing and the plants they are working in. If there are any spores or pests on the clothing, it is less likely they will migrate to the plants. Saunders Brothers employees wear disposable, plastic pant and boot covers while working in boxwood houses. Boxwood Blight spores can stick to tools and clothing moving from location to location, so instead of worrying about having fresh clothes, disposable pant/boot covers are the perfect solution.

This is also a great tool for landscapers that may visit many sites in a day. Instead of having to change or sterilize clothing, wearing disposable pant and boot covers greatly reduces disease or pest movement from site to site.

Sterilizing tools/equipment:

Pruning crews as Saunders clean their tools with alcohol between each house.

Even large equipment like digging machines are cleaned with sterilant between fields.

Sterilizing tools and equipment is an easy, practical step to take towards growing cleaner plants. It is a good practice to carry around a spray bottle of isopropyl alcohol. Research shows that a 50% isopropyl alcohol solution is effective at killing most plant diseases. Alcohol spray can be used to clean any handheld tools such as pruners, shovels, or trimmers. Other options of sterilants are a 10% bleach solution or Lysol® spray. Many researchers also recommend hydrogen dioxide products such as Zerotol® 2.0. Make sure to always check labels before you use any products. Most of these products are very user-friendly and are labeled to clean tools, equipment, or even surfaces.

Dragging a hose through a bed of infected plants and then moving it through a healthy bed could spread diseases. Taking an extra minute to spray the hose down with a sterilant could avoid a bigger cleanup in the future.

Cleaning Stations/Sectioned growing areas:

Cleaning stations in the field nursery.

Cleaning station in the container nursery.

This tip takes a bit more planning than some of the other suggestions, but might have the biggest pay off if you ever run into a disease or pest problem. Saunders Brothers has set up both their field and container nurseries in sections. In the container nursery, boxwood are grown in specific locations separated by roadways. In the field nursery, areas are sectioned based on geography. Each section has a cleaning station that all employees must visit at they enter and exit. Cleaning stations are stocked with:

• Disposable pant/boot covers

• Trashcan

• Boot bath and brush

• 70% Isopropyl alcohol spray/liquid hand sanitizer.

• High pressure water hose (field)

Crews using a cleaning station to rinse off their shoes and equipment.

Upon entering and exiting the area each employee must:

Entering:

• wear rubber boots, easily washed boots, or disposable boot covers

• step in boot bath/wash boots

• put on disposable pant covers

Exiting:

• remove and trash disposable pant covers or spray pants

• step in boot bath/wash boots

• wash hands/ use hand sanitizer

• rinse off tools, then spray with alcohol

This is an example of the sectioned boxwood production areas are at the containers nursery at Saunders Brothers.

The perks of setting up these sectioned areas is that in the event of an infection, you can quarantine one area, and continue production from the other locations. Consequently, each time a person or a crew enters a new area, they are cleaning off any potential pests or diseases.

Establishing cleaner growing protocol doesn’t have to be a daunting task. Taking some steps early on in production can help set you and your plants up for success while combating common pests and diseases. Consider these tips and find what works for you.

Benefits of Mulching Boxwood

Boxwood in the landscape with a think layer of mulch.

Mulching is a common landscape practice that is used to suppress unwanted weeds, reduce evaporation from the soil, and encourage proper soil ecology and structure while being visually appealing. Recent research has also shed light that mulching can be an effective tool to aid in pest and disease management. Earlier this year, Virginia Tech published data from a two-year study showing that mulching can be a great tool to help prevent Boxwood Blight.

The experiment was set up in two locations, one being an old nursery in Low Gap, North Carolina and the other a residential landscape near Richmond, Virginia, both previously devastated by Boxwood Blight. This field trial consisted of both mulched and non-mulched treatments and was done for two years under normal environmental conditions. The goal of this study was to evaluate mulch as a physical barrier to prevent the soil inoculum from splashing onto healthy plants.

The fungal pathogen Boxwood Blight (Calonectria pseudonaviculata) produces heavy, sticky spores on diseased leaves that fall to the soil. There is no evidence to date of the pathogen attacking boxwood roots, so it was thought that providing a physical barrier of mulch would prevent the inoculum from splashing onto the leaves where the pathogen can affect the plant. The experiment used containerized ‘Justin Brouwers’ boxwood which are known to be highly susceptible to Boxwood Blight, that were rotated through mulched and non-mulched plots at 1-to-2-week intervals.

A freshly mulched bed of NewGen Independence® and perennials.

Results of the experiment showed clear distinction between the mulched and non-mulched plants. The mulching reduced the number of Boxwood Blight lesions by up to 97%! Even the scientists working on the project were amazed by the unbelievable difference that mulch made. Although for a long time it was thought that mulching boxwood plants was a bad idea but, this study shows that it can be an exceptionally effective tool for Blight control. Below you will find a downloadable PDF of these findings. Saunders Brothers Nursery worked with Chuan Hong and his team to provide plant material for the experiment.

Boxwood blight is a multi-faceted disease that can be overcome with smarter growing practices and understanding. Mulching has been proven to be another very simple and accessible tool that can help prevent this disease.

Boxwood Site Selection and Irrigation

Boxwood being used as a hedge in a landscape.

Boxwood are known for low maintenance and longevity in a landscape, but in order to ensure such timelessness, it is important to select the best site for the plant. When properly planted and cared for, boxwood are easy to maintain. Paying extra attention at planting will ensure a flourishing plant for years to come.

In choosing the proper site, we recommend the following:

Several boxwood in a shady site.

• Choose the best cultivar based on size, shape, growth rate, maintenance, and exposure.

• Take a soil sample and have it tested. Look for areas of good drainage with a pH in the range of 6.5-7.0.

• Prepare a proper hole, making sure to plant the boxwood “high” with 2 inches of the root ball above the soil line. Be sure that water drains away from the plant and does not puddle near the root ball.

• Water thoroughly at the time of planting and maintain adequate but not excessive irrigation through the first couple of years.

Once the boxwood is properly planted, it is very important to water it. A thorough soaking at the time of planting is essential. This will probably be the most important watering this plant will ever have. Make sure to fully soak the root zone.

Boxwood being irrigated first thing in the morning.

Once this initial watering is complete, periodic watering should take place as needed. Allowing the root zone to dry between irrigation events will encourage root growth. We recommend approximately 1 inch of precipitation or irrigation per week for the first 1-2 years. Pay close attention during the hot and dry summer months, so that the boxwood does not stress. It is also important to pay attention that the plants have adequate moisture as winter approaches. In the Mid-Atlantic region of the United States, boxwood will continue to grow roots in the winter when the temperatures are still mild.

The arrows show holes on the drip tape where the irrigation water escapes.

Here the drip tape sits on top of a bed of field plants.

Drip irrigation is the ideal method for watering boxwood. Simple drip systems can be installed under the mulch and will offer thorough irrigation without wetting the foliage. In a drip system, water seeps from the drip tape without splashing. It enters the ground without puddling and conserves water. The rate of water from drip tape is very low, maybe a quarter of an inch per hour per emitter. Fungal diseases such as Boxwood Blight can be spread through water splashing that may occur with sprinkler methods of irrigation. If drip irrigation is not an option, make sure overhead watering takes place in the early morning, giving the leaves ample time to dry. It is important to never water boxwood in the late afternoon or evening because wet foliage through the night can lead to diseases and stress on the plant.

Raised beds ready for boxwood planting. It is very important that boxwood are planted “high” to avoid water pooling around the roots.

In 2018, Central Virginia had an annual rainfall of close to 90 inches, about double the normal amount. Boxwood throughout the region showed signs of stress, particularly those plants that were constantly in standing water. Whenever you plant boxwood, envision what the immediate landscape will look like after 3 inches of rain, and plant the boxwood in such a way that ensures water never puddles around the roots.

Giving added care before planting, boxwood are destined to succeed and maintain a timeless elegance in your garden.