Japanese andromeda (Pieris japonica) is a useful broadleaf, evergreen shrub in the same family (Ericaceae) as holly, rhododendron and mountain laurel. It is valued in the landscape for its resilience in conditions common to Northeast gardens and sometimes difficult to fill: light shade and moist, mildly acidic soil. Admired for dramatic flower display and colorful new leaves, Japanese andromeda has the added benefit of being low maintenance and highly resistant to deer damage. Native to densely growing, mountain regions of Japan, southern China and Taiwan, this plant has been bred for diversity of flower color, stature and vivid, year-round interest.
There are an extraordinary number of cultivars available. Plants put out brightly-colored emerging leaves in early spring and long-lasting, early season flowers in drooping clusters of delicate bell shapes, colored from red-purple to silver-white. Flower buds can also be spectacular in color, on bright stems, ornamenting the garden in winter. Slow in growth, plants range from dwarf 3 foot plants to over 10 feet tall. These shrubs often have an asymmetrical growth habit that can be splendid as a garden showpiece but are especially pleasing when planted in groups or massed with other broadleaf evergreen plants.
Japanese andromeda is not without a few practical problems. Most plants are hardy from USDA zones 5 to 7 which means they may need some protection from strong sun, particularly in the afternoon in the New York City area which is on the margin of their comfort zone. Like many plants of woodland origin, they are sensitive to drought and prefer soil that is fast-draining and rich in organic matter. Avoid a windy siting to reduce winter dieback. Proper siting and planting and timely pruning improve your chance of success and enjoyment of this plant.
Poor siting is the most common problem with growing Japanese andromeda. New York City is on the warm edge of the zone in which Pieris japonica is hardy. In a marginal location, it is particularly important to site the plant in the right conditions to avoid a gradual decline in vigor or a sudden deterioration when the weather is extreme. Sun and wind protection are critical, and soil must be fast-draining, rich, and acidic.
Hardy in USDA zones 5 to 7 (sometimes 8), Pieris japonica prefers a slightly shaded location that resembles its woodsy native habitat. In particular, site plants to avoid harsh, late afternoon, sun exposure from the west. Lace bugs, a common problem for this plant, are mostly an issue if planted in a hot, sunny location. Keep in mind that shrubs will also need some shade in winter, when the leaves have fallen off deciduous trees and taller plants. Exposure to strong winter winds should be avoided to protect from winter dieback, but air circulation around the plant is important in reducing the incidence of disease.
Soil should drain well, as this plant won't tolerate waterlogged or compacted conditions and can succumb to root rot. Additions of organic compost will probably be necessary when you prepare the planting area and proper systems to enhance drainage may be needed. Soil should look chunky and rich, like a forest floor.
Soil pH should be acidic in the 4.5 to 6 range, or Pieris will be unable to take up the nutrients it needs from the soil. Sulfur amendments may be incorporated into the soil to reduce pH and make your soil more acidic if necessary. Elemental sulphur and aluminum sulphate are the two products most commonly used for this purpose. Read the label of your selected product carefully to understand the time it will take to achieve reduced pH, protective warnings and the amount of product necessary. Products may take a number of months at specified temperatures to achieve good results. The soil pH will not be altered permanently, and regular soil testing and amendment may be required. If you don't know the pH of your soil, you can have it tested in the lab of your county's Cooperative Extension office.
Pieris is an evergreen shrub and will occasionally take up nourishment from the soil through the colder months. It should be planted at a time of year that is not too challenging for it to establish its root system, neither too hot nor too cold. Early fall (September) or spring (April) planting are best as long as the weather is cooperating, and the warmest and coldest temperatures have passed.
To plant, dig a hole 2 to 3 times as wide as the shrub's root ball and the same depth. When planting, give each plant some room for sunlight and good air circulation. Do not plant where other root systems will be in competition.
Mulch around the plant to maintain soil moisture. Leaf mulch, pine bark or composted pine needles are good mulches to help maintain a low pH value. Do not use a pebble mulch.
Japanese andromeda are at home in slightly moist and well-drained soil. Keep the soil uncompacted by adding some organic compost each spring. Mulch to hold in moisture in summer and winter. In weeks without significant rain, especially in the hottest months, irrigate soil, avoiding splashing on plant leaves. (Splashing water can propel fungal disease.) Many problems can be avoided by preventing the plant from becoming drought stressed.
After planting, apply an inch of composted bark chips, composted pine needles, leaf mold or any suitable, permeable, organic mulch. The mulch will help retain moisture in the ground and maintain the cool, moist conditions needed at the roots. Remember not to mulch right up to the base of the shrub (leave 6 inches from the trunk) or you'll create a damp environment that is an open invitation to pests and disease.
Remove the layer of mulch in the spring and replace it with fresh mulch, over moistened soil, once the earth has warmed up. Gently tidy and re-mulch in the fall after the soil has completely frozen through, as a layer of insulation.
Do not over-fertilize. Amending the soil lightly with organic compost in the spring will help it to retain a loose, fast-draining texture and enables the plant to benefit from rich, organic matter it requires. Keeping the pH near the correct range is important because nutrients in the soil are only available to the plant under those conditions. The best way to determine whether the soil needs additional nutrients or pH adjustment is by testing it. If your soil is not naturally low in pH, test it annually to see if additives are needed.
Each Pieris variety has a distinctive size and shape. You can prune to remove dead or poorly placed branches and even to rejuvenate the form of the plant, but your andromeda is still going to tend toward the ultimate shape it was bred to be. Choose wisely to select a cultivar that fits well in the site. If you begin pruning away just the dead or diseased wood as well as awkward branches while plants are young, you can maintain their natural form and avoid the need for corrective pruning later.
Japanese andromeda pruning is best done just after it blooms. This gives the plant time to put on new growth and set its buds in the fall for the following spring. Pruning more than a month after blooming puts next year's flowers at risk. Remove up to 1/3 of the branches by cutting individual branches by up to 1/3 its length, just above a node or taking 1/3 of the branches off entirely, back to a main stem. The first techniques creates a tidier plant and the second is used to gradually rejuvenate a plant and open it up for better air flow.
Sometimes Japanese andromeda gets so big or leggy that gardeners choose to prune in the fall and risk losing all of their flower display in the following spring. You can reduce the branches by up to 2/3 of their overall length for a drastic rejuvenation but not without drawbacks and risk to the plant. Fall-pruned Japanese andromeda may still produce some flowers in the next season, but far fewer of them because most of the buds have been cut off. You will also lose most of the bright winter buds in your garden. (In the following year, everything will be back to normal.) There is an added danger of winter dieback to fall-pruned plants that should be noted. Plants will be stimulated to put out tender new growth after pruning which is at greater risk in cold temperatures. Branches may die back to beyond the point of pruning and endanger the strength of the shrub.
Summer pruning is not a good idea because hot weather pruning stresses the plant unnecessarily.
Shrubs may need to be protected from wind and salt spray during the coldest months depending upon the degree of shade and protection afforded by their site. These evergreen plants will continue to photosynthesize for an extended period, and even on occasion during the winter, but will be challenged to take up the necessary moisture from the dry or frozen soil. Sunny days will wake up south- to southwest-facing plant tissues then plunging night temperatures will stress the plant. Wind blowing past the leaves will speed up evaporation creating even dryer conditions and a greater stress on the plants.
If your Pieris is not in a naturally protected site, the use of burlap fastened to stakes to create a wind break for the location is a good idea. Do not wrap the shrubs closely with burlap or their access to sunlight will be restricted and dampness will be held against the leaves. (Wrapping completely should be considered if your shrub is in a position that is likely to be subject to forceful deposits of snow from a roof ledge, snow plow or other source. Otherwise, brush off heavy snow that settles on the plant to avoid crushing injuries.)
If the shrubs are near a path or roadway that is treated with salt in the winter, positioning the windbreak to also prevent salt spray on the plants will increase their chance of making it through the winter in good health. Use plant-friendly ice-melting products on your property.
Take measures to see that Pieris japonica are watered until the ground freezes and during any warm breaks in the winter weather.
Pieris are early spring blooming with buds breaking dormancy in March, when weather conditions tend to be unpredictable. The early flowers are a joy but also a vulnerability. Freezing temperature once the plant experiences the environmental triggers that cause buds to drop their protective winter scales can result in a loss of flowers.
Japanese andromeda that are unprotected from winter wind are likely to experience dehydration, like many other broadleaf evergreen plants. The wind can remove moisture from leaves at a time when the ground is frozen and the plant cannot bring enough water up from its roots to make up for the loss from its leaves. The result is brown, dry leaves. Exposure to strong sun can make matters worse. It may lead to cracking bark when temperatures fluctuate too rapidly from warm, daytime sun to frosty night. Complete desiccation of leaves will cause them to curl and turn brown and, along with winter sun scald, can lead to branch die-back. If leaves are merely curled and damaged in spots, the plant is likely to recover when warmth returns.
These problems can be reduced by keeping the plants as healthy as possible and by planting the shrubs in a protected and partly shaded site. Screening the shrubs is another option. Finally, clear any snow or ice accumulation off the plant directly so that the weight does not cause limb breakage.
A plant with wide, brown patches on the leaves may be planted in a position without adequate sun protection. Take care to avoid any site with afternoon sun or near a hot or reflective structure. Plants in challenging locations will need extra water in weeks without an inch of rain to help combat sun-related stress.
It is not uncommon in our area for Pieris to lose their vigor with age and have fewer leaves and flowers. Endeavor to maintain the acid pH, organic richness and fine drainage of the soil to improve performance. Do not allow the environment to become overly shady as your garden grows. Remember to protect the plant from desiccating winter winds with a wind break and mulch the roots to reduce summer and winter weather stress.
Remove spent floral structures right after flowering. The plant will look tidier without those bare brown stems. Don't wait! New buds begin forming in summer and remain on the plant through the winter. You can see an example of the tiny chains of buds in the winter photo above, though colors will vary with variety.
Pieris browning and die-back of branches is more likely to be related to environmental conditions than to disease or pests. Stress issues resulting from cold (described above) or water are the most common. Providing the plant with about one inch of water, every week, from spring until ground freeze, is a good rule of thumb. (Sometimes rain will do this work for you.) Do not water from above the leaves as splashing water is a significant vector of disease.
If the proper site preparation and planting is not carried out, drainage can be an issue. Compaction of soil around plants, due to foot traffic or construction, will disrupt the permeability of the soil and the plants will suffer due to loss of water, oxygen and root growth.
Broadleaf evergreen shrubs are vulnerable in times of temperature extremes and more so if they are in containers. The container means that the roots of the plant are closer to the surface and less insulated than they would be in the ground. In winter, even plants that would be hardy in our area may find the additional cold they experience at the root too challenging. They will also warm more quickly in a period of mild winter temperature, so the whipsaw is greater. Summer heat will more directly affect the plant's roots.
Begin by choosing a plant that is well-sized for container growth (there are some recommended selections on the next page) and a container that allows adequate room for the root system of the plant with a margin of soil to insulate it. Remember that dark containers will heat up and expose your plant's roots to greater heat fluctuations in winter sun and heat extremes in the summer.
In all other matters, care for evergreen shrubs in containers as you would those planted in the ground. Water them well in the late fall so that they are in top condition when the temperature drops. Once the soil has frozen, mulch the top of the container, but do not allow the mulch to creep up the stem of the plant or clump under the leaves where it can harbor disease. Do not mulch deeply or the roots can be starved of air and water. Be mindful of water needs in the summer. The more protected the location of the container (protected by building structure, awning, other plants), the less likely you are to need extra barriers to protect container-planted shrubs in winter.
Dirr's Encyclopedia of Trees and Shrubs by 
