Here we go in-depth into boxwood topiary foliage care for any grower to know for survival from planting, watering to pruning, and more topics to consider.
Boxwood is easy to maintain when properly planted and cared for. We recommend the following to increase your enjoyment of this timeless plant.
Take care to select the proper cultivar of boxwood in your planting zone. Consider the boxwood’s desired ultimate size, shape, and growth rate. Anticipate maintenance requirements, the sun exposure of the site, and the climate of the site.
Before choosing a boxwood cultivar for a specific location, consider the timing and intensity of the sun in the area to be planted. All boxwood will do well in shady areas, while some of those same cultivars will also do well in sunny locations. Sunny locations are areas with bright sun from late morning to late afternoon. Part-sun locations are shaded from late morning to late afternoon but may receive direct sun early or late in the day. Shady locations typically receive no direct sun. Some cultivars of boxwood will bronze in winter more than others. To lessen winter bronzing, avoid the direct afternoon sun.
Consider drainage before selecting a site or planting a boxwood. When choosing a site, avoid areas that have poor drainage. Avoid any area with standing water or outlets for gutters or other drains. Some cultivars are more tolerant of areas with questionable drainage; however, all boxwood will perform better in areas when the plant is elevated and drainage is addressed.
Digging the Proper hole
Dig the hole twice (or more) as wide as the root ball. Dig the hole so that about 1/4 of the root ball is above the original soil surface. Planting the boxwood high helps to ensure proper drainage. Never plant boxwood level with the soil surface. Take care when the soil has been disturbed below the root ball to ensure that the plant remains elevated and does not settle with time.
Proper soil preparation is essential to ensure long-term success with any planting. Take soil tests in advance of any bed preparation. Based on the results of the soil test, modify the soil to achieve a pH in the range of 6.5 to 7.2. Before planting in an existing bed or new area, we recommend you renovate as much area as possible. This will improve drainage, reduce compaction issues, introduce new soil nutrients and organic matter, and encourage root growth.
Renovations of existing areas or new plantings should include removal of unwanted existing plants and debris, the incorporation of soil amendments, and soil mixing. Turn the soil to a minimum depth of 10-15 inches and add amendments. Examples of soil amendments include: compost to increase organic matter, gypsum to break up heavy day soils, aged poultry litter for organic matter and nutrients, and limited amounts of peat more than 20% amendments. The amended soil should resemble the existing soil to encourage root growth beyond renovated areas. If an excess of amendments and new soil is added, the roots of the plant will often not venture beyond the new soil.
Once you prepare the bed and dig a hole, place the plant in the hole remembering to keep about 1/4 of the root ball above the original soil surface. Backfill the hole with the amended soil. Mound the soil up to the edges of the root ball. Do not place soil on the base or trunk of the plant and ensure that the plant remains elevated and does not settle with time.
A thorough soaking at the time of planting is the most important watering a boxwood will ever have. Afterward, periodic watering’s on an as-needed basis, is best. They allow the root zone to be thoroughly wetted then dry again before watering. It generally takes about 18 months for a boxwood to acclimate to a new site. During this time, monitor the plant weekly for adequate moisture. Never allow the plant to dry to the point of showing stress. When boxwood shows stress due to lack of moisture, they seldom recover completely.
Mulching a boxwood helps in many ways. Mulch retards weed growth, helps retain moisture in dry periods, decomposes to create additional organic matter, moderates soil temperature, and reduces erosion.
Maintain about one inch of mulch around a plant but never place mulch on the trunk of the boxwood, Re-mulch as needed every two years or so. Shredded hardwood mulch works well; also, composted leaves, pine needles, and pine bark make good mulches. These types of mulches are beneficial because with time they decompose and create organic matter. Take care to not use “green” or un-aged mulch as it requires extra nitrogen from the plant. Some gardeners prefer stones or oyster shells as mulch but understand that they provide decreased benefits about moderating soil temperature and moisture retention.
The best time to transplant boxwood in central Virginia is early September through mid-November. In your area, choose a time in the fall when the summer heat has begun to subside and before severe cold sets in. Some gardeners have success transplanting during mild winters. Proper timing will allow for maximum root growth through the winter when moisture is typically more abundant and in turn, better prepares the plant for dry seasons ahead, when feasible, the root ball should be dug at least as wide as the canopy of the plant. The root ball size will vary but a rule of thumb should be for every 3 feet in width, the depth should be 1 to ½ feet. Boxwood has shallow roots so focus more on root ball width than depth. Never transplant boxwood during the stress of summer heat or severe drought. Water thoroughly before transplanting as well as immediately after planting and then monitor moisture for 18 months until the plant is established. Never allow the root ball to dry out when above ground or allow the plant to dry to the point of showing stress. Once drought-stressed, boxwood seldom recovers completely.
Fertilization and Liming
Boxwood typically does not need a lot of fertilizer. Use soil tests to determine fertilizer needs as well as the pH of your soil. Boxwood thrives when the pH of a soil is between 6.5 and 7.2. A pH below 5.8 can cause problems in boxwood, especially in Buxus Sempervirens ‘Suffruiticos’. The optimal time to fertilize is in late fall.
Boxwood roots grow the most in late fall, winter, and early spring when soil temperatures are more moderate. Late summer and early fall fertilization may cause a plant to initiate top growth that could be burned with early freezes.
Always place fertilizers near the drip line of the plant and never under the mulch, Boxwood typically have feeder roots just under the soil surface. Placing fertilizer directly on those roots can cause damage to the plant. The American Boxwood Society recommends using a fertilizer with a formulation of 10-6-4. Using aged poultry manure at low rates both at the time of planting and as needed for the life of the plant. Bagged cow manure has also been proven beneficial by many gardeners as a source of fertilizer as well as organic matter.
Proper pruning techniques are crucial to long-term success with boxwood. Pruning techniques differ with each cultivar. It is important to choose the correct cultivar for the desired use and location to avoid the need for excessive pruning.
The best time to prune boxwood is in the late winter to early spring before the plant breaks dormancy. This is usually March in central Virginia. This minimizes the time between pruning’s may stimulate late fall growth that could be burned by early winter freezes. Early winter pruning, while not detrimental, leaves pruning scars on the plant until the spring flush is initiated.
In general, any pruning that increases the airflow in boxwood is advantageous. Cultivars that are more sunlight penetration to the interior of the plant. Thinning is typically done by reaching into the plant and breaking or cutting out branches with hand pruners. These branches can be 6-10 inches long on larger cultivars, or only a couple of inches on a dwarf cultivar. This will leave pockets or holes in the plant for air and sunlight penetration. Using hand pruners will results or holes in the plant for air and sunlight penetration. Using hand pruners will result in a cleaner cut and lessen the possibility of disease introduction. Not all cultivars require annual thinning; however, those that benefit the most from thinning are noted in the cultivar section of the Boxwood Guide. Typically, cultivars that are sheared regularly will benefit from thinning.
Larger and more vigorous cultivars are generally tolerant of shearing or more radical pruning techniques. Use lopes or shears to drastically reduce overall plant size on vigorous plants, taking care to leave one-half to two-thirds of the foliage undisturbed. This foliage will produce the energy the plant needs to recover. Plants that require more drastic pruning may need to be pruned over several years to reduce the overall size in steps and not jeopardize the plant’s health. If a Buxus ‘Suffruticos’ (English) overgrows its intended space, use loppers to ensure clean cuts on large branches. The plant should develop new foliage along the bare stems. Full recovery may take several seasons. You should never use shears on English boxwood. Using shears increases the density of the canopy of the plant long-term as well as shatters brittle limbs thus increasing the chance of disease. To minimize radical pruning, do not select large cultivars for applications where small plants would be more suitable. See specific notes in the cultivar section of the Boxwood Guide on boxwood pruning.
Some dwarf cultivars including ‘Green Pillow’, Grace H. Phillips’, ‘Morris Dwarf’, and ‘Morris Midget’ will occasionally sport or send up a branch of foliage that is very vigorous compared to the rest of the plant. Remove the sport by cutting into the plant below the point where the sport appeared. Sports on plants do not hurt the plant, but they can be unsightly. Some boxwood enthusiasts will propagate sports in hopes of finding a new desirable cultivar.
Boxwood is drought tolerant once established. The best irrigation systems are designed to water boxwood only until they are established and then only occasionally in times of severe drought. After this point, boxwood needs minimal irrigation. Too much water is often more harmful than not enough water. Avoid watering daily and or methods of irrigation that keep the foliage wet for long periods.
New plantings should receive deep watering’s about once a week for the first 3-6 months. Always monitor soil moisture before irrigating. Boxwood will do best when they are watered thoroughly by wetting the root zone to a depth of 12 to 18 inches. The root zone should then be allowed to dry before the next application of water. The timing of subsequent watering will be dependent on rainfall and soil conditions. Allowing the soil to dry between applications encourages stronger root systems as plants are forced to search for water. Avoid allowing the plant to dry to the point of showing stress as they may have difficulty recovering. The first 18 months after planting are the most critical for irrigation.
Established plantings over 18 months old require supplemental water only in times of extreme drought. A good rule thumb is: If there is adequate rainfall that your lawn needs to be mowed, your boxwood should be fine.
Simple drip irrigation systems installed just under the mulch work well for boxwood. They allow for the slow application of water through the root zone area. Lawn irrigation systems should be designed and maintained to avoid the daily application of water onto the foliage of boxwood.
Avoid over-watering boxwood. Some cultivars, especially Buxus sempervirens (Americans), ‘Suffuiticos’ (English), ‘Jensen’, ‘Elegantissima’, ‘Vardar Valley’, ‘Justin Brouwer’, and other Sempervirens cultivars, are susceptible to root rot resulting from continuously wet or soggy soil conditions or poorly-drained soils. Remember, roots need air as well as water.
Avoid cultivation near the roots of boxwood. Boxwood roots are shallow and widely spread. Cultivating near the drip line of the plant creates problems in boxwood. This is especially evident when boxwood is used as edging in a bed. For example, if one side of the plant is restricted in horizontal root growth by a “hard edge” like a sidewalk or manufactured edging, and the opposite side is tilled 1-2 times a year for planting annuals, severing the roots repeatedly will cause long term problems and potentially kill the plant.
If you need to cultivate where there is a “hard edge” on one side of a boxwood planting, stay about one foot from the drip line of the plant. When the side opposite of cultivation is not restricting horizontal root growth, you may cultivate slightly closer.
Winter and Cold Damage
Occasionally boxwood will be damaged by late fall freezes, extreme winter cold, or late spring freezes. Damage can be as minimal as a few bronzed or desiccated leaves, to broken and dead plants. Most of the boxwood listed in the Boxwood Guide is hard to Zone 5 or 6. Refer to the individual cultivars for specific hardiness information.
If a late fall freeze damages any new growth, prune off unsightly branch tips. Do not do this until after the first freeze or two of winter. Otherwise, wait until late winter or early spring to prune, Additionally, we have seen bark splitting near the ground level of some boxwood. This typically happens to boxwood that has bare trunks and is exposed to the southwestern sun. Bark splitting is the most common Buxus Spervirens ‘Sufruiticosa’ (English).
To minimize root damage due to extreme cold, newly-planted boxwood should be deeply watered before the roots freeze. Filling the air space around the root system with water helps to insulate the plant. Boxwood in containers is especially at risk of winter damage when they are not watered well.
Foliage bronzing in the winter can be attributed to sun exposure and cultivar selection. Direct sun in the winter (especially from the southwest) will tend to bronze some cultivars more than others. Bronzed leaves typically begin greening up in the spring as temperatures begin to rise and as new foliage covers them. Intense sun on shade-loving cultivars will cause bronzing that does not recover quickly in spring and can cause long term problems. If you want to minimize bronzing, take care to avoid southwest exposures, and consider your varietal selection. Good choices would include “Green Beauty’, ‘Jim Stauffer’, ‘Dee Runk’, ‘Vardar Valley’, Fastigiata’, Justin Brouwers’, and sempervirens (American). The “Green Series” (‘Green Velvet’, “Green Mountain’, ‘Green Mound’, ‘Green Gem’), as well as some of the dwarf cultivars of boxwood, tend to bronze in the winter sun. Refer to the cultivar section of the Boxwood Guide for more information.
In snowy conditions, it is best to leave the plants alone and let the snowmelt on its own. However, when there is a chance of breakage, gradually remove the snow by gently brushing the limbs in a manner to minimize the breaking of branches. Remember; if branches are frozen, beating them will cause damage to the limb and bark, and will encourage the introduction of disease. Many of the microphylla cultivars are rigid and will hold snow with minimal to no damage. In a heavy ice storm, leave the ice on the plants to melt naturally. Diseases will often wait for conducive conditions before invading the damaged plants, a process that can take six months to a year more.
Occasionally in late spring after new growth has begun to emerge, an early morning frost will damage the new growth on a boxwood. Pruning off affected foliage is not necessary as the plant will typically regenerate on its own. In most cases, a second flush will begin within days and cover any burned foliage.
Boxwood in Containers
Boxwood is an excellent choice to use in a container. Cultivars that are suitable for containers are listed in the cultivar section of the Boxwood Guide under Uses. When planting in a container, take care to select a container that is larger than the root ball of your chosen plant. If you allow space for the roots to grow, the boxwood will have a longer life in the container. Use an artificial potting medium to fill around the root ball. Be sure the container has drainage holes in the bottom.
After several years it may be necessary to remove the plant from the pot to re-invigorate it. Cut and loosen the roots, and replace much of the soil to stimulate new root growth on the plant before placing it in the same or larger container. When the roots stop growing, a plant typically will begin a deteriorate. Fertilize lightly annually or biannually with a well- balanced fertilizer that does not drive down the soil pH (see Fertilization, page 7).
Although boxwood is more drought tolerant than many plants, be sure to provide adequate water throughout the entire year, including the winter. In winter the plant must be well-watered before extreme cold spells. Filling the air space around the root system with water helps to insulate the plant. In summer, water about once a week, Regularly monitor water, and keep roots moist but not wet.
Boxwood Foliage Propagation
Boxwood is a simple plant to propagate. Propagation procedures differ with every nursery and gardener. Typical cutting propagation occurs in late June After the spring flush has had time to harden off, through early October. Do not propagate too late into the fall or winter, unless artificial bottom heat available, as the cuttings need soil temperatures in the low 70’s to begin rooting. Make cuttings 4-6 inches long and remove one-third to one-half of the foliage. Apply a rooting hormone to the bottom of the cutting before it is stuck in the rooting bed.
Rooting bed media is typically a combination of sand and peat moss. Cuttings should be shaded from any direct sun until rooted. Keep the foliage moderately moist until roots develop to increase rooting success. Do not attempt to propagate boxwood from mid-March through early June as the energy of the plant is being directed into producing new top growth.
Many gardeners use layering to propagate boxwood. The natural weight of limbs or snow can push a branch down so that it touches the ground. The portion touching the ground will root into the soil. After a while, the branch can be cut from the parent will root into the soil. After a period of time, the branch can be cut from the parent plant and moved. Other gardeners, typically in the spring, will bend a side branch of a plant down to the soil and lay a brick or rock on top of it. In the fall or the following spring, the plant can be cut from the parent plant and planted elsewhere.