Check newly planted boxwood on a very regular basis especially the ground moisture in the soil surrounding them. The summer can be a very stressful time for boxwood planted during the spring. Check to determine whether they are stressed as indicated by dieback, off-color in the foliage, or a crispy feel to the leaves.
Unfortunately, if any of these conditions exist to a great extent the plant may already be terminal. Nevertheless, immediate action should be taken. First, checking the soil condition will determine whether ample moisture is present (see watering below).
Secondly, if the plants have not been thinned, plucking may be helpful to reestablish the balance between the root system and the foliage. Remove any dead wood as this will not produce any new leaves. If a branch bends, but does not snap, do not remove it because it is not dead. Thirdly, shading the plants with burlap to protect from the hot mid-day, and afternoon sun will provide a cooler environment for the plant to recover.
Watering: The water needs of boxwood are a function of a number of factors. Sandy soil will not hold water as long as clay soil. Plants in the shade will not need as much water as those in direct sun. Plants which experience reflected heat from walls or adjoining sidewalks/driveways will need more water than those in cooler environments. The key point is to water deeply. A soaker hose placed along or around plants is an excellent way to water deeply and simultaneously conserve water. Alternately, a hose placed at the base of a plant to drip for a period of time is very satisfactory. Standing and watering by hand is not satisfactory because most people do not have the patience or time to thoroughly saturate the ground. Larger plants need a larger area watered and proportionally more water, consequently more time is needed for a slow thorough soaking. Watering needs are lessened by mulching. Newly planted boxwood going through their first summer have greater water needs since the root system is not completely established. A soaker hose covered in mulch both conserves valuable moisture and provides a pleasing appearance.
When boxwood are stressed from lack of water there is a considerable time delay before the plant actually looks like it is stressed. Therefore, assessing water needs on the basis of the appearance of the plant is unsatisfactory. The only reliable way to determine whether there is sufficient moisture present is to assess the moisture condition of the ground around the plant, being careful to avoid damaging the roots. I have a very tried and true method of assessing watering needs of boxwood. It is called the “get on your knees and get your hands dirty method.” You cannot rely on the fact that you watered it two days ago or two weeks ago. Get on your knees with a garden trowel and dig around the outside of the plant but not too close. Boxwood roots are very close to the surface so dig outside of the drip line where there are fewer roots. Dig down 2-4 inches and assess the level of moisture in the ground. You should be able to easily tell if the soil is dry needing water or sufficiently moist.
Cultivation and weed control: Boxwood roots are very shallow so digging around the base of plants should be avoided. Hand pull grass or weeds when the soil is moist in order to minimize soil disturbance. Again, mulching is beneficial and an excellent way to control weeds. Plastic laid down with mulch over it should be avoided. See section on “Plastic” for a detailed explanation of why it is not only ineffective but actually harmful to the soil environment.
Thinning, propagation, and cleaning: The best time to thin plants is late winter before new growth, but it may still be done during the summer without harm. See “Plucking.” Summer is an excellent time to propagate. See “Propagation” for a detailed description of this topic. This may be done any time after the new growth has thoroughly hardened off (about July 1). Cleaning the inside of plants is important in maintaining them in a healthy, disease free condition because debris which accumulates in boxwood holds moisture. The moisture leads to aerial roots and a positive environment for the growth of disease. A strong water hose spray directed throughout the interior of the plant is usually sufficient to clean the plant and summer is an excellent time to perform this preventative maintenance. Doing the cleaning when the soil is dry is especially helpful since it will add much moisture to the ground right around the plant.
Stephen D. Southall
English Boxwoods of Virginia