“I’ve heard that cutting through the roots around the drip line of a tree or shrub with a shovel can encourage it to flower. Is that true?” -Ben

The technique you’re referring to is a rejuvenation practice known as “root pruning,” in which roots are cut in order to control growth. While it can work, it wouldn’t be my first choice. I’d start by making sure the plant is getting adequate light, water, and nutrients before resorting to such extreme measures.

Think of it this way: when you cut the roots of a shrub or tree, the plant draws in upon itself and puts its resources toward its own survival and continuation of the species. It does this by increasing flowering and fruiting and by compacting both its root ball and its growth. Root pruning is normally used to strengthen and prepare trees and shrubs for the shock of transplanting, and for training container plants (well-timed root pruning is an integral part of the practice of bonsai).

If a tree or shrub is overgrown and no longer blooming, root pruning may indeed rejuvenate it. Using a sharp shovel, make deep cuts into the soil around the plant in a circle at least 2-3 feet in diameter. Some gardeners cut the entire circle; others make cuts with spaces in between. Remember that the more roots you cut, the more stressed your plant will be, so compensate with regular watering for several weeks until new roots form. Prune roots in late fall or early spring when the plant is dormant.

About Crape Myrtles

With literally hundreds of sizes and colors available, crape (or crepe) myrtles are a terrific, low-maintenance choice for prolific blooms during hot, humid summers. Nowadays, many varieties are hybrids that maximize the colorful blooms of the common crape myrtle (Lagerstroemia indica) and/or the distinctive bark, cold hardiness, and disease-resistance of the Japanese crape myrtle (Lagerstroemia faurei).

Crape myrtles bloom in midsummer, with colors including white, lavender, purple, pink, magenta, and red. After blooming, they develop distinctive seed heads, then the leaves tend to fall toward the end of autumn, leaving the colorful, exfoliating bark for the winter.

Exfoliating bark gives year-round beauty.

Selecting Crape Myrtles

Crape Myrtles truly come in every possible size and shape, from knee-high shrubby dwarf plants to towering tree forms, so it is possible to choose a variety that exactly fits your purpose. When choosing crape myrtles for your yard, there are several factors to consider including:

• Height
• Natural shape (shrub vs. tree)
• Flower color
• Amount of bark exfoliation
• Disease resistance

Printable list of crape myrtle varieties (PDF 61kb)

Fading blossoms enrich the color palette of this deep red variety.

Planting and Growing Crape Myrtles

Crape myrtles can be grown in USDA hardiness zones 6-10, although in zone 6 they’re likely to die back to the ground in winter. They like humidity and, once established, can tolerate quite a bit of drought. They flower best in full sun (at least six hours per day). As for soil, most any kind will do, as long as it’s well-drained. The ideal soil pH is neutral to slightly acidic.

Ideally, crape myrtles should be planted in cool weather when they’re dormant. Dig a hole twice the size of the root ball. Soil amendments are usually unnecessary unless you’re amending the entire planting bed – small pockets of high-nutrient soil can prevent the roots from branching out properly. Plant your crape myrtle at the same depth it was in the nursery pot, and backfill with loosened soil. Then water thoroughly and apply 3-5 inches of mulch.

Seed heads can be removed, or left for late-season interest.

Water newly planted crape myrtles at least once a week if dormant and in cool weather, and up to five times a week if planted during hot weather or in very sandy soil. Water new plants regularly for about two months, and water during drought for better blooms and healthier plants.

Crape myrtles benefit from annual feeding with a general-purpose or high-nitrogen fertilizer, in early spring as soon as you see leaves. If you want to fertilize twice, do the second application about two months later. Slow-release fertilizer can help prevent rapid sucker growth that is vulnerable to diseases and insects. Take advantage of the toughness of these plants – too much fertilization can actually result in excessive leaf growth and fewer blooms!

Size and Pruning Crape Myrtles

Depending on the variety, crape myrtles can have different shapes. The miniature, or dwarf, varieties are generally bred to have lots of branches, and they tend to look shrublike and shouldn’t need pruning unless they are growing unevenly. Medium and large varieties tend to develop sucker growth, or small shoots at the base of the trunk. These may be pruned off if desired, and the entire plant may be pruned according to your tastes. For varieties that bloom before mid-July, deadheading can often result in a second blooming.

Crape myrtles bloom on this year’s new growth (sometimes called “new wood”), so prune during late winter before growth starts. Fall pruning, especially in warm climates, can result in a quick growth response that prevents dormancy and makes winter freezes potentially deadly.

There are two schools of thought, and quite a bit of debate, about larger pruning jobs. Some gardeners like to lop off all stems at a uniform height each year, leaving branch stubs in the winter that flush out into a ball of growth in the spring. This is useful if you want a uniform border and height control, but it can result in bunchy growth and knobby stems that may be more susceptible to aphids and disease.

Other gardeners decry this method as “crape murder” and adopt a less aggressive approach that conforms more to the natural size and shape of the plant. Most growers and researchers agree that only light pruning is necessary for plenty of blooms, so the choice is really yours.

To achieve a graceful tree shape that shows off the lovely bark, first remove all but 3-5 strong trunks. Then remove lateral branches on the bottom half of the tree. Make “heading back” cuts on long, leggy limbs to encourage branching. Don’t overprune in the beginning – make the basic cuts and then allow the plant to grow, and continue shaping over time.

The best decision about the size of your crape myrtle is made when you buy it. Buy the right variety to fit the space! If you buy a 15′ variety and try to keep it 7′ tall, you will prune yourself silly. Instead, buy a 7′ variety, and you will find yourself with an incredibly low-maintenance plant.

Pests and Diseases for Crape Myrtles

The most common scourge of crape myrtles is powdery mildew – particularly during hot, humid days followed by cool, dewy nights. Another common problem is leaf spot (Cercospora lythracearum), which looks like dark brown spots on the leaves, which then turn yellow and fall off. Both can be controlled with a general fungicide, and some cultivars are more resistant than others. Crape myrtles can also be affected by root rot (caused by poorly-draining soil), and sooty mold (caused by the excretions of pests such as aphids).

Further Information

• Crapemyrtle Varieties, Clemson University
• Crape Myrtle Culture, University of Georgia
• Crapemyrtle Q&A, U.S. National Arboretum
• Crepe Mytle Issues, Mobile Press-Register

Well pruned shrubs and trees are a hallmark of a carefully tended yard or garden. Foundation plantings are lush and full, and blooming shrubs display their blossoms on shapely branches that accentuate each plant’s unique style.

In addition to proper planting, watering, and fertilizing; pruning is an important practice for promoting plant health and enhancing the natural size and shape of landscape plants. Pruning is easy—a basic understanding of plant growth, and a few simple techniques, and you’ll be ready to go.

Tools

Most pruning tools have an arc-shaped blade, which makes short work of slicing through small branches. “Scissor action” pruners involve two sharp blades sliding past each other “Anvil cut” pruners have one blade slicing against a wide, flat surface. While scissor action pruners are more expensive, they usually make the cleanest, closest cuts.

Hedge clippers have long, straight blades. They are used for cutting small, green branches and tips and are best reserved for shearing formal hedges. Pruning saws come in a variety of shapes and sizes, with blades designed for larger branches and small trunks.

Make sure blades are kept sharp and oil them periodically. To prevent the spread of plant diseases, clean and disinfect pruning tools after use.

Proper Timing

Spring-flowering shrubs, such as these, should be pruned immediately after blooming:

• Andromeda
• Azalea
• Chinese Redbud
• Fringe Tree
• Kerria
• Mock Orange
• Philadelphus
• Pieris
• Roses
• Spiraea (early varieties)
• Mountain Laurel
• Viburnum
• Syringa (Lilac)
• Japanese Quince
• Pearlbush
• Star magnolia
• Weigela
• Rhododendron
• Deutzia
• Forsythia
• Lonicera

Shrubs that bloom in summer and fall, and shrubs grown primarily for their foliage, can be pruned in early spring, before growth starts:

• Abelia
• Callicarpa (Beauty Berry)
• Hydrangea
• Spirea (late varieties)
• Summersweet
• Crape Myrtle
• Snowberry
• Barberry
• Lagerstroemia
• Boxwood
• Buddleia (Butterfly Bush)
• Clethra
• Hypericum
• Bluebeard
• Shrub Althea
• Coralberry
• Chaste Tree
• Hibiscus
• Privet
• Ilex (Holly)

The soft, green growing tip of a branch is called the “terminal bud.” This bud produces a hormone that affects the growth of side branches. The biology of basic pruning is simple: if you remove the terminal bud, the lateral buds below your cut will be stimulated to grow into more branches. If you leave the terminal bud, the branch will grow longer instead of thicker.

Choosing the Branches

Start by removing any of the branches illustrated below that don’t belong.

Next, look at your shrub with a critical eye while considering the following questions:

• What is this shrub’s natural size and shape (rounded, arching, tree-like)?
• What is the design purpose of this shrub (hedge, foundation planting, specimen plant)?
• Does the plant growth need to be influenced to achieve that purpose?
• Is the shrub healthy and growing evenly?

A well-pruned shrub looks natural, and in most cases doesn’t look like it has been pruned at all. If a shrub’s natural shape does not suit your taste or needs, consider moving it and planting one that is better suited for that location.

Making the Cuts

There are five basic techniques for pruning shrubs. Most pruning jobs will involve a combination of techniques.

1. Pinching back: Simply use your fingers to pinch off the terminal bud of the branch. This will encourage lateral branches to form and can be a great way to prevent more pruning later on.

   

2. Heading back: This method removes the terminal bud, resulting in more branches. Cut the branch at an angle, about ¼” above a branch bud and sloping down and away from the bud. The branches about 6” to 8” below your cut will be stimulated the most, so keep that in mind when choosing where to cut. The bud nearest the cut determines the direction the branch grows, with the outward facing bud usually resulting in the best shape. If a heading cut is made in the middle of a branch with no bud, the result will be a flush of growth at the site of the cut.

   

3. Thinning: Thinning involves removing branches while leaving the terminal bud. Make the cut just outside the branch collar, which is the bulge where the branch meets the stem, but don’t leave a stub. Thinning can produce a more open, shapely plant, without altering its overall size, shape, or growth habit.

   

4. Renewal or rejuvenation pruning: Renewal pruning involves removing the oldest stems and branches at the base, then thinning or heading back the younger stems to promote regrowth. With rejuvenation pruning, the entire shrub is cut to stubs less than 12”. This drastic measure is usually done if a shrub has become an overgrown, tangled mass that is not blooming well.

   

5. Shearing: Shearing involves trimming off the tips of branches and is best used only for formal hedges. Shearing alters the shrub’s natural shape and promotes thick growth only on the exterior of the plant, which results in dead foliage and lack of growth on the interior branches.

   

For most shrubs, pruning is a forgiving task - once you learn how each plant grows, you can correct previous pruning mistakes as you go. With a little practice, pruning becomes intuitive and is a quick way to revitalize your yard or garden.