Besides the dryness of summer, winter is one of the harshest times of the year on boxwood. The most severe stress comes from the combination of cold winter winds and frozen ground, thus not allowing water to move up into the plant. Either one of these stresses alone is not as dangerous as the two in combination. Winds cause plant desiccation (drying) and the moisture must be replaced. If the roots and surrounding soil are frozen, this replacement is not possible. The plant can tolerate frozen roots if there are no winds to cause excessive desiccation. On the other hand, wind can be tolerated if the roots are capable of supplying moisture to the top of the plant. The importance of monitoring winter moisture levels is sometimes not realized until the spring when the effects of winter dryness are seen in a damaged plant.

Early spring is a good time to assess any damage of the previous winter and take corrective measures when necessary. The alternate freezing and thawing of the ground will possibly leave exposed roots which need to be covered with a fresh layer of soil or mulch. The mulch also provides the all important organic matter necessary for good plant growth.

Reddish-brown rust or bronzing color is often seen on plants during the winter before spring growth. Commonly referred to as “winter burn,” its cause is most probably not due to the winter but to the pH of the soil being too acidic (on the lower side of 6.5, see section on “Soil samples and pH”).

The seriousness of winter burn may be evaluated in two ways. First, feel the plant to determine if the leaves are soft to the touch or whether they have a crispy, paper feel to them. The latter indicates a level of dryness which may be terminal, at least for that part of the plant. The second test is to look at the color of the leaves within the plant. If these deeper leaves are the proper shade of dark green and are soft to the touch, then the outside leaves are probably showing the result of lack of nutrients and the bronzing is exacerbated by exposure to wind and cold.  Spring growth, will often reestablish the plant to its normal color. This winter burn however is most probably due to a lack of nutrition which in turn is caused by a low pH. This situation does NOT necessarily mean immediately adding fertilizer. Getting a soil test is advised since the pH of the soil will determine whether the plant is able to take up the available nutrients from the soil.  Just as one would never “take pills” before doing blood work and going to their doctor to determine what is wrong, one should never throw fertilizer at a weakened plant without taking a soil sample to assess the condition of the soil.  The pH advised for boxwood is around 6.5-7.2. Often the soil becomes too acid and regardless of the nutrients in the soil or the amount of fertilizer applied, the plant is unable to take up the nutrients because the pH is off balance. The addition of lime will bring the pH back to the proper range and allow the plant access to the nutrients.  See the section on “soil samples and pH.”  The proper amount of lime to be applied will be specified with the soil sample results.

Late winter/early spring before new growth comes out is a great time to pluck and shape misshapen plants since the new growth will quickly provide a uniform appearance and cover any cosmetic blemishes from the plucking. See the section on “plucking.” This time of year is also an ideal time to break out any dead wood. If plants contain winter debris such as dead leaves, a strong hosing out and cleaning is advised. If plucking results in healthy cuttings which may be used for rooting, late winter/very early spring is an excellent time to do this rooting. See the paper on “plucking” and/or on “propagation.”  Late winter and very early spring is also an ideal time to move plants which need to be transplanted. See “planting paper.” Only early fall is a better transplanting time. As soon as major freezes are over, usually around March I for the middle Atlantic states, transplanting can begin (depending on the winter, January and February might also be acceptable transplanting times).  The concept to remember is that you want to provide the maximum amount of time between planting and the dryness of the upcoming summer.  During the fall, winter, and very early spring, top growth will not come out but root growth will take place any time the ground temperature is significantly above freezing.

One of the surest signs of a healthy plant is a timely overall flush of new growth. This is normal and should occur. If it does not then a soil analysis may be in order to determine if nutrient deficiency exists. When grown in well-drained and aerated soil with good organic matter, the fertilization needs of boxwood are minimal. The fertilizer normally applied to a lawn is often sufficient to provide the needs of boxwood. If application of fertilizer is called for after a soil analysis, a slow-release type is preferable since it will supply nutrients to the plant over a longer period of time. Apply around the base of the plant in very early spring before new growth, being careful not to touch leaves with the fertilizer. An alternate time is in late fall, after frost has come. The frost will stop any new top growth which otherwise may occur with fertilization.

Stephen D. Southall
English Boxwoods of Virginia

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