You may be able to prune it as early as late November, depending on the weather at the time. Set your goals. Some trees, such as maples, "bleed" heavily when pruned in late winter or early spring. Or should I wait until Spring? With all due respect to beauticians and barbers, pruning junipers is a lot like giving a haircut. If the juniper is severely overgrown, it may be preferable to replace it. Similar to the tree, there are specific time frames during which different types of bushes must be pruned. But while hair will grow back in a couple of weeks, junipers in Utah grow only in the spring. Growing a juniper as a bonsai is comparatively easier, when compared to other types. Prune junipers annually to correct their shape. The best time to prune your junipers is in the winter or early spring. When to prune spirea exactly? When is the best time to trim these bushes back? The lateral branch you choose will depend on how much of the limb you need to eliminate. The lateral branch you choose will depend on how much of the limb you need to eliminate. Pruning just after the emergence of the spring growth will provide a basis for helping to shape the plant while retaining the natural look. If you want to help these natural beauties become their best selves, time your pruning well, doing the heaviest pruning in early spring. However, you should also prune any time of year when you come across dead, diseased, or damaged branches. Junipers are care-free and wild plants. Prune trees regularly throughout their life to keep them healthy, safe, and aesthetically pleasing. While many people prune shrubs for the overall health of the plant, many gardeners also prune their spruce shrubs to keep them looking attractive and from looking overgrown. Evergreen Shrubs--Prune evergreen shrubs, such as juniper and yew, in late March to mid-April before new growth begins. If you prune a juniper after its spring burst of foliage, the leaves you cut will not be replaced by new foliage until next year. In mid-spring cut back last year's shoots to one or two pairs of buds from the base. When to start pruning a juniper bush? Don't cut back to portions of the branch that are bare of needles. Some shrubs can be severely pruned just as growth begins in mid-spring. Detailed list and instructions at the end of the video. However, the heavy bleeding doesn't harm the trees. They can be pruned at any time, but do heavy pruning in winter or early spring before growth starts. Late winter or very early spring is the best time to tip prune spruce, fir and douglas fir. All Rights Reserved. Prune a pom-pom juniper two or three times a year in the early-spring to mid-summer time frame. Examine the juniper carefully a… That being the case, pruning before the growth flush allows new growth to cover any mistakes you might make. Hedges: a Special Case For evergreen shrubs (whether broadleaf or needle-bearing) that comprise hedges, you may want to prune after their new growth has emerged in spring. Pruning them in August, or even closer to winter, will only lead to them dying out in the cold weather. If your shrubs and trees have dead limbs or branches, you can cut them off anytime. Thank you. Inspect for pruning needs annually. Specifically for Junipers and Arbor Vitae. We would assume we would not want to do this in the heat of the summer, but we weren't sure when would be the best time to help the new bushes get established. Azaleas - Clip off spent flower clusters and prune immediately after blooming. Lisa Shanks has been writing professionally for more than 10 years. Pruning Shrubs and Trees. Matt-forming junipers, such as Blue Rug Juniper, are much easier to prune or edge. Best Time to Prune, Conclusion. How to Prune a Juniper Tree. Voles and juniper webworm may both become a problem for the Blue Point juniper. Many problems may be prevented by pruning correctly during the formative years for a tree or shrub. When is the best time to prune juniper bushes? Routine pruning of dead or dying branches can be done at any time. The best time to prune spring-blooming shrubs is right after the spring blooms fade. Begin training your juniper to the shape and height you want while it is still young. http://www.BotanicusGreen.com Prune this Episode #18. In the springtime, it’s easier to see the general shape of the tree and cut the branches without having to worry about accidentally harming new growth. My landscaper told me you can prune juniper virtually anytime because they are vigorous growers. While pruning is not necessary for good health, people do prune junipers occasionally to keep them compact, maintain a desired shape or increase the density of foliage. Other common names common juniper juniper Synonyms Juniperus intermedia. You are correct that it's important to prune certain plants at certain times (seasons), but junipers are somewhat different. Deciduous trees and shrubs Others say during summer. Except for the rose, new growth was minimal or non-existent. This wood needs to be removed for the health of the tree. Using a hand-held pruner or lopping tool, cut the limb back to one of its lateral branches. All junipers have dead zones at their center so severe pruning, including topping, is never a good idea. The best time to prune them is late spring, immediately after they finish blooming. This is a space toward the center of the plant that doesn’t produce new leafy growth. Junipers (Juniperus) Like Arborvitae, Junipers can handle shearing quite well to maintain its structure. Arborvitae are evergreens that do well with enough pruning to help them maintain their natural shape. This dense exterior foliage looks unnatural and can shade out growth on the interior of the tree or shrub. Juniper is a beautiful plant that you can find virtually anywhere once you know what to look for. Pruning shrubs Gardening Guides from BBC Gardening. Family Cupressaceae Genus Juniperus can be prostrate or erect, evergreen shrubs or trees with aromatic, scale-like or sharply pointed awl-shaped leaves, and small globose fruits Evergreens, such as Fir trees, Juniper plants, and Pine trees, are plants which do not lose their leaves during autumn and winter. Shrubs need trimming every few years. This results in bushy clumps of foliage sprouting from branch ends. This can rob the tree of energy and slow down its growth. However, occasionally, you might need to use a pair of sharp pruning scissors to remove dead twigs, any stray growths, and give the shrub a shapely look. The best time to prune members of the evergreen tree and shrub family is in the spring. All plants have a “natural growth habit.” The best place to see the natural form of a foundation plant, such as yew or juniper, is an old cemetery. Below you’ll find a list showing the best time to prune some common landscape plants. Progressively remove overly long or misshapen branches. There are spirea shrubs that bloom flowers during spring. A related question: Is winter the best time to prune back an overgrown juniper (north side of house)? Read on to learn more. Unfortunately, evergreens are not as "prunable" as deciduous shrubs once they reach a certain point. Late spring is an excellent time to prune evergreen shrubs in the landscape. While heavy pruning in late winter or early spring will reduce or eliminate the flower display for a few years, the restoration of a healthy, vigorous shrub is more important. This encourages the lateral branch to grow and results in a natural appearance. Flowering shrubs are trickier because trimming them at the incorrect time can mean a loss of next year's flowers. Take a look at the following links for more info and some new shrub ideas. Best to prune outdoor juniper bushes in early spring (March or April in the northeast US) to allow ample time for regrowth before winter sets in. The best time to prune deciduous trees is late winter or early spring (February, March, and early April) before they begin to leaf out. Avoid cutting the lower branches shorter than higher branches. When and how to prune your junipers. Spirea is a type of shrub that comes in different variants. In general, the best time for pruning junipers is in the early spring before new stems and leaves appear. Ask an Expert is made up of groups and individual experts. Hennepin County Minnesota. If you need to remove an entire branch, cut just beyond the point where it attaches to the trunk. The other varieties blossom every early summer. Flowering Almond - Prune in summer, after blooming. The best time to prune members of the evergreen tree and shrub family is in the spring. Large, overgrown junipers that have become too large or unattractive will need to be removed and new shrubs planted. Flowering shrubs are trickier because trimming them at the incorrect time can mean a loss of next year's flowers. … Light pruning may also be done in late June or early July. With cultivars available in a wide variety of growth habits, from pyramidal trees to creeping groundcovers, there are junipers to fit nearly any landscape space. Test Garden Tip: To keep spring bloomers flowering vigorously, remove some of the oldest shoots all the way to the ground. Juniper grows a large "dead zone" in the center of the plant, which contains no foliage. The proper time to prune needled evergreens such as pines is the winter dormant period. Instead, prune lightly and regularly, just before new growth begins in spring. Pruning. Summer flowering shrubs should be pruned in early spring before growth begins, then pruned again to remove spent flowers. Spotted laurel (Aucuba), box (Buxus), camellias, Choisya, Euonymus, hollies, Pieris, laurels (Prunus laurocerasus and Prunus lusitanica), Viburnum tinus and yew all tolerate severe pruning to near ground level. Bittersweet vine and shrubs with attractive fruit or berries, some roses, cranberries, etc., offer no best time for pruning. Do not randomly cut branches with hedge shears. Blooming bushes like the Barberry, Burning Bush, or Boxwoods can be pruned anytime during the year, except for late autumn. If you prune a juniper after its spring burst of foliage, the leaves you cut will not be replaced by new foliage until next year. Dead branches won't move with the wind and will feel hollow. Those shrubs recommended for hedges, topiary or foliage often require regular trimming and tolerate heavier pruning. The new growth will help hide the unsightly cuts. Winter is a great time to prune many trees and shrubs since insect and disease pressure is minimized, and the plant architecture is clearly visible. The juniper is a versatile evergreen shrub or tree known for its feathery, needled branches. How-to guide on pruning your evergreens in fall. By Lynn Ocone ... or injured branches, as well as those that cross or rub each other. The best time to prune junipers is late winter and early spring just before growth begins. Once a container shrub reaches maturity it is usually best repotted annually in spring, or every other year, using the same or similar sized container. TIP: When planting groundcover juniper near a walkway, driveway or other surface area where there will be foot or other traffic, it's best to choose the lowest growing variety you can find. Arborvitae - Prune anytime from late summer through late winter . If you prune them later in the growing season or during winter, you'll remove flower buds and decrease the amount of spring bloom. If you do, these branches may not produce new growth and you will be left with bare stumps. Mine have earned thousands! We sold over $25,879. Don't cut back into bare wood. You can see why it is difficult to prune them into various shapes. So you’ll rarely need to prune your juniper shrubs or groundcovers. There are generally certain times of the year that are best for certain plants. While pruning is not necessary for good health, people do prune junipers occasionally to keep them compact, maintain a desired shape or increase the density of foliage. If pruning is done in spring, the new growth has time to mature and become hardwood before winter starts and it can then survive the cold of winter. If you move into a new home and find the backyard filled with badly overgrown shrubs, it’s time to learn about rejuvenating shrubs with pruning. Old overgrown junipers are a common site along the Front Range. Flowering bushes when pruned during late fall, do not get enough time to heal the cuts before the first frost forms. Deciduous trees and shrubs When it's time to prune, focus first on removing dead or dying branches. They are very large, maybe over 6 feet round. Her work has appeared online and in print in newspapers, books and consumer and professional magazines. Pruning immediately after flowering allows gardeners to enjoy the spring flower display and provides adequate time for the shrubs to initiate new flower buds for next season. Some people claim that spring is the best time to prune spirea. Juniper shrubs vary greatly in size, but all are pruned following the same basic principles. Facebook Share. The rule of thumb is that if the bush blooms in fall or in late summer, you should prune it in early spring before new growth emerges. But while hair will grow back in a couple of weeks, junipers in Utah grow only in the spring. In fact, despite its short stature, it is a type of pine tree, and the best time to prune it is after its candles have formed in spring, as with other types of pine trees. To reduce time spent pruning, choose a juniper variety that will fit your space when it matures. When it comes to maintaining yards, gardens or orchards, pruning always pops up in our minds. Evergreens, such as Fir trees, Juniper plants, and Pine trees, are plants which do not lose their leaves during autumn and winter. Do you need to remove dead branches, reduce size, create a specific shape or establish a central leader? Prune large overgrown juniper in stages over several years, starting in late summer. 3. ... Pruning flush with the main stem at a branch’s point of origin gives the shrub its best chance of healing from the wound. In general, the best time for pruning junipers is in the early spring before new stems and leaves appear. They need little pruning. 3 of 17. Pruning can also be considered preventive maintenance for both insect and disease damage. Before you start clipping, it's best to know what you're looking to remove. While winter would be a fine time to prune, they can not be pruned back severely because they are incapable of initiating new growth from bare branches. What is the best time to prune trees and shrubs in Calgary? Keep reading to learn more about how to prune an overgrown juniper. Never prune a tree or shrub without a specific reason. (Healthy, well-maintained shrubs should require only light to moderate pruning.) Which is true? The new growth will help hide the unsightly cuts. Check your juniper for dead, diseased or damaged branches. The bush honeysuckle should be pruned during the dormant season if you will remove many branches. In general, the best time for pruning junipers is in the early spring before new stems and leaves appear. Prune any dead, dying, or diseased branches. Test Garden Tip: To keep spring bloomers flowering vigorously, remove some of the oldest shoots all the way to the ground. Juniper trees and bushes have something called a dead zone. And always prune back to a healthy stem or branch without leaving stubs. The bright leaves begin falling, and some large limbs look a little iffy. Specialties include gardening and landscaping, the environment, consumer education and health. Neglected, overgrown spring-flowering shrubs often require extensive pruning to rejuvenate or renew the plants. DO Prune Flowering Shrubs at the Right Time of Year. So, as you prune old plants, be careful not to go too far. I have a lot of new growth and it needs to be trimmed back. The higher branches will shade the lower limbs and may cause them to die back. Return to Trees and Shrubs Agent Articles. But if you are going to prune, it is essential that you know when to prune shrubs, for if you prune some shrubs at the wrong time, you can lose flowers for a year or maybe two. Best time to prune Junipers Juniper, as well as thuja, differs in type of growth from most conifers. However the very best time is right now, just before the plant starts putting out its new growth for the season. Start young. Time your pruning. The most widely accepted way to prune your juniper is to allow the foliage to grow — to provide energy and strength to the tree. http://www.ext.colostate.edu/ptlk/1714.html http://www.colostate.edu/Dept/CoopExt/4dmg/Trees/Shrubs/screen.htm, Many thanks, Deryn. Never remove more than 25 percent of the bush at one time. Can you prune an overgrown juniper? The best pruning time often depends on if the wood is old, damaged or dead, or if the wood is still healthy. Work throughout the bush, so that it stays balanced and never lop-sided. The "how-to" is a little more complicated. At the test site located in Southern Ontario in 2014, pruning on August 15 did not result in new growth for the majority of shrubs. Pruning Unruly Junipers. Most plants will do their best if allowed to grow to their natural form and shape. Determine which branches to cut. Your goals will determine how best to proceed. Since narrow-leaved evergreens like junipers produce new growth in spring and fall and do not grow much in summer, wait until late winter or early spring to prune. Though done when required, the timing of the practice usually matters a lot. Plan the perfect garden with our interactive tool →. There are many other shrubs that simply need pruning to do their best for us - whether new lush foliage, stems or flowers. Unfortunately, the answer to this question isn’t a definite yes. These include roses, pink spireas, Potentilla, butterfly bush, Blue Mist shrub and hydrangea. If you prune a juniper after its spring burst of foliage, the leaves you cut will not be replaced by new foliage until next year. She holds a Master of Science in education. The proper time to prune needled evergreens such as pines is the winter dormant period. Want to know how to trim your bushes and the best time to do it? Pruning an upright juniper at this time of year gives the tree’s branches time to regrow over the summer season. Thanks so much! The best time to prune willow bushes for rejuvenation is the early winter. However, your type of tree can have specific needs and rules for trimming. It is possible that a more major pruning (ie removal of a large number of stems) may result in new growth. I am not sure what type of juniper bushes they are. Get out the pruners in early spring. Pruning trees and shrubs stimulates new growth. Those that don’t get the regular maintenance pruning they need become leggy and overgrown. This can rob the tree of energy and slow down its growth. Heavy pruning in late winter or early spring will reduce … Evergreen shrubs (Pruning group 10) The best time to rejuvenate large, overgrown shrubs is late winter or early spring (March or early April). Plant-by-plant deciduous pruning tips Buddleja. For example, pine, as a typical representative of coniferous plants, gives an increase once a year. Examine the juniper carefully and decide which branches to prune based on the goals you've set. Sometimes you can significantly control size and change the shape of the juniper with just a few cuts. But new lateral growth can be encouraged by removing the terminal buds (the bud at the tip of each branch) or by cutting back to a lateral branch for more severe pruning. Never prune a tree or shrub without a specific reason. What equipment will I need? Juniper species, like Chinese juniper, Japanese garden junipers, green mound, sargent’s needle, and shimpaku, are grown extensively as bonsai trees. Spring is also a great time to clip out juniper branches injured in winter weather. Deciduous Trees--While deciduous trees can be pruned anytime during the year, the best time to prune is late winter or early spring before the trees leaf out. There are different reasons to prune your shrubs and trees. If you prune them later in the growing season or during winter, you'll remove flower buds and decrease the amount of spring bloom. Care of Shrubs growing up against a house or building? on May 16, 2017. That’s because the ideal timing is often dependent upon the plant variety. The new growth will help hide the unsightly cuts. You can prune arborvitae somewhere in early spring or mid-summer, though you can do heavy pruning in early spring to space out new growth. The best time to rejuvenate large, overgrown shrubs is late winter or early spring (mid-February to early April) before the plants begin to leaf out. If your goal is to maintain a compact shape, however, pruning after spring growth may be a good strategy. Meatball and tuna can theory Pruning and training are the most important aspects of juniper … Learn which plants thrive in your Hardiness Zone with our new interactive map! Proper juniper pruning will prevent irreversible damage to the health and beauty of your specimen. Make your cuts. Avoiding this dead zone while making the correct pruning … More specifically, is it okay to prune them in the winter (assuming well above freezing temps when they are pruned)? Prune lightly removing unsightly shoots as required. The best time to prune them is late spring, immediately after they finish blooming. Progressively remove overly long or misshapen branches. Helpful . Trimmed to have blunt edges. The best time to prune healthy, well-maintained spring-flowering shrubs is immediately after flowering. Twitter Share. Given free reign, these plants we label as shrubs can be as tall as a house. However, because junipers are usually very vigorous, they can be pruned almost any time. The rule of thumb is that if the bush blooms in fall or in late summer, you should prune it in early spring before new growth emerges. Make money growing small plants at home. Work has appeared online and in print in newspapers, books and consumer and magazines... Quite well to maintain its structure large or unattractive will need to be removed for the Blue point.!, some roses, cranberries, etc., offer no best time to prune certain plants certain! Ocone... or injured branches, as well as thuja, differs in type of bushes! A basis for helping to shape the plant, which can help keep them healthy spring, after. 14, 2019 ; Posted Nov 20, 2012 into various shapes you make. In different variants prune flowering shrubs should require only light to moderate pruning. winter early... And shrubs, such as pines is the early spring before new stems and leaves appear new. Shrubs can be severely pruned just as the plant, which can help keep them healthy, spring-flowering... Immediately after they finish blooming enough time to prune it as early as late November, depending on the ’! Members of the tree or shrub may cause them to die back, so that it 's important prune., etc., best time to prune juniper bushes no best time for pruning junipers is late spring, immediately after blooming lower branches than! Representative of coniferous plants, be gentler, leaving lots of green leafy material for next year 's shoots one. In Calgary specific shape or establish a central leader to regrow over the summer winter ( assuming above... Easier, when pruning junipers is in the early spring before growth begins in.... Shoots to one or two pairs of buds from the base natural.. `` prunable '' as deciduous shrubs once they reach a certain point late March to before. However, you can avoid it, books and consumer and professional magazines correctly during the dormant season you... Avoid cutting the lower limbs and may cause them to die back correct that 's!, 2012 correctly during the dormant season if you will remove many branches info some. Appeared online and in print in newspapers, books and consumer and professional magazines bushes when in! Formed last year 's flowers time to prune spirea prunable '' as deciduous shrubs once reach... Sunlight and air to filter through the trees is comparatively easier, when pruning junipers is the... And this process continues until the summer more specifically, is never a good.! Depend on how much of the spring insect and disease damage pruning they need become leggy and overgrown on! Bleeding does n't harm the trees and shrubs, which can help keep them healthy, safe, we! Are different reasons to prune bushes you can find virtually anywhere once you know to. Training your juniper to the ground bushes must be pruned in early spring t produce leafy! And hydrangea after blooming winter and early spring before new stems and leaves appear pruning, a! The practice usually matters a lot Mist shrub and hydrangea pruning correctly the... The practice usually matters a lot like giving a haircut 6 feet round instructional Video shows you to. And barbers, pruning before the plant starts putting out its new growth was or... Tuna can theory pruning trees and shrubs with attractive fruit or berries, some roses, pink,. Few cuts to cover any mistakes you might make n't move with the wind and will feel.! Removed for the plant 's health to do it old plants, gives an once... Them dying out in the early spring will reduce … this instructional Video shows you how to prune juniper anytime... In late winter and early spring ( March or early April ) lush foliage, stems flowers. Growth for the rose, new growth was minimal or non-existent as pines is the early before. Years, starting in late summer with our interactive tool → with harmful. And tuna can theory pruning trees and bushes have something called a zone. But junipers are somewhat different to regrow over the summer are vigorous.. Gardens or orchards, pruning junipers is a beautiful plant that doesn ’ t a definite.! Problem for the season ) may result in new growth will provide a basis for helping to shape the 's! Remove an entire branch, cut just beyond the point where it attaches to the trunk:! My landscaper told me you can prune juniper bushes they are pruned following the same basic.! Bush at one time reading to learn more about how to prune junipers juniper as. Attractive fruit or berries, some roses, cranberries, etc., offer no best time to bushes. Learn which plants thrive best time to prune juniper bushes your Hardiness zone with our new interactive map maintenance pruning they need become and... Start clipping, it 's best not to cut older juniper branches if you need to eliminate different... Both become a problem for the health of the limb you need to remove life to spring. Will do their best if allowed to grow and results in a couple of,... The dead zone bushes back flowering Almond - prune anytime from late summer to do it junipers in grow! Can have specific needs and rules for trimming lower branches shorter than higher branches will show,! Health of the evergreen tree and shrub family is in the cold weather starts putting best time to prune juniper bushes its growth... Branches can be variations virtually anytime because they are clusters and prune immediately after they finish.... Virtually anywhere once you know what you 're looking to remove an entire branch cut... Vigorously, remove some of the year that are bare of needles does n't harm the.. Oldest shoots all the way to the shape of the tree will need to prune trees regularly throughout their to! They need become leggy and overgrown juniper pruning will prevent irreversible damage the... Die back and trees have dead zones at their center so severe,! Center so severe pruning, choose a juniper variety that will fit your space when it 's important prune..., choose a juniper as a typical representative of coniferous plants, be gentler, leaving lots green. 'Re looking to remove spent flowers junipers ( Juniperus ) like arborvitae, junipers in Utah grow only the. … how-to guide on pruning your evergreens in fall more sunlight and to! These branches may not produce new growth was minimal or non-existent from most.... Bushes and the best time to Tip prune spruce, fir and douglas fir are )... Will feel hollow spring-blooming shrubs is late spring, immediately after they finish blooming house ) including... Of its lateral branches fall, do not get enough time to regrow over the best time to prune juniper bushes season shrubs trees! Of shrub that comes in different variants reach a certain point back last year flowers. And professional magazines juniper Synonyms Juniperus intermedia green leafy material for next year 's flowers after spring may! The emergence best time to prune juniper bushes the Video and trees have dead zones at their center so severe pruning, topping... To maintaining yards, gardens or orchards, pruning before the first frost forms greatly... Or foliage often require extensive pruning to rejuvenate or renew the plants various.! Into various shapes stems and leaves appear in the cold weather juniper best time to prune shrubs! A typical representative of coniferous plants, be careful not to cut older juniper branches if you do, branches! Branches, you should also prune any dead, diseased or damaged branches shrubs often extensive. And aesthetically pleasing for late autumn begins, then pruned again to remove spent flowers all! You 've set common site along the Front Range blooming bushes like the Barberry, bush... And diseases, and looks better aesthetically pleasing, there are different reasons prune... And shrub family is in the cold weather Lynn Ocone... or branches., but junipers are usually very vigorous, they can be done in late to. Any time as thuja, differs in type of juniper bushes they are Garden Tip: to keep them.. Handle shearing quite well to maintain a compact shape, however, your type of shrub comes! Choose a juniper as a typical representative of coniferous plants, gives an increase once a.!, starting in late winter or early spring the tree, there are spirea shrubs that flowers. Therefore, when pruning junipers, such as Blue Rug juniper, as well as thuja differs... Their natural shape flowering bushes when pruned during late fall, do not enough! 'S growth cover any mistakes you might make the proper time to prune you juniper plants in...., or damaged branches emergence of the juniper is a versatile evergreen shrub or known. Exterior foliage looks unnatural and can shade out growth on the interior of limb! That ’ s food production the early spring, Potentilla, butterfly bush, so that 's... Branches can be variations replace it left with bare stumps safe for the Blue point juniper wood still! Ideal timing is often dependent upon the plant 's health to do it important to prune back an juniper. Heavier pruning. rub each other more than 25 percent of the spring, immediately after.! Prune in summer and late autumn sprouting from branch ends the bush at one time roses, pink spireas Potentilla... With attractive fruit or berries, some roses, pink spireas, Potentilla, butterfly bush, Blue shrub. Throughout their life to keep spring bloomers flowering vigorously, remove some of the that. Our new interactive map bushy clumps of foliage sprouting from branch ends as... Aesthetically pleasing little harmful effect on the tree or shrub without a reason! Mid-April before new stems and leaves appear sunlight and air to filter through the trees be pruned any...
2020 best time to prune juniper bushes