29 January 2018

Shrubs Prune and Rejuvenate

15-feet tall Burford Holly shrubs
This is an ideal time of year to prune shrubs either to reshape, clean up or completely rejuvenate them.

Rejuvenation or renovation pruning can mean taking shrubs completely to the ground or just above the ground. When done to healthy shrubs, they will quickly grow from the stump and via new stems.

The Burford Holly shrubs in front of our house began as one-gallon container size from Lowe's. They were precisely planted the same distance apart and allowed to grow there with minimal trimming for 16 years. Now they are 15-feet tall and 20-feet wide.

 Since they are evergreen, they are a great privacy screen from the dog walkers, bicycle walkers, cars and pedestrians. In addition, I can sit on the screened front porch in privacy. However, they've reached a point where they have to be rejuvenated: They are too big for their space, too tall to top prune and have almost leaves inside their woody structure.

Not all shrubs are amenable to this hard a cutting so pruning back by one-third or one-half is quite a bit safer. Shrubs that have lots of twigs and stems are likely candidates. These include Burford Holly, Dogwood and Viburnum. Junipers will not re-grow from that dead center; they must be removed and replaced.

Older shrubs that have not been pruned in several years become poorly shaped and have quite a bit of bare wood inside. Cutting them back hard, focusing on the older stems and branches for removal, makes the entire shrub younger with newer branching.

Alden Lane - January pruning
One way to go about the process is to remove one-third to one-half of the growth late-winter and then finish the pruning and shaping when new growth begins in the spring. We're removing a bit less than half of the green branching, all the dead and damaged branches and most of the crossing branches.

After removing dead, broken and diseased limbs, remove crossing branches. All cuts should be made just outside a swollen branch collar, leaf or leaf bud.

Avoid damaging the bark: Don't wiggle the pruning tool, use tools with sharp blades and use the right size pruner. Never leave a stub - see bottom center illustration on right.

One of the goals of pruning is to allow sun to filter into the center of the shrub so new growth can be forced away from the outer edges. On our mature shrubs there is as much as 3 or 4 feet of bare branch inside with a foot or two of green growth at the end of the branch.

Rose pruning El Paso Master Gardeners
Rose pruning is a different topic but the illustration is helpful to indicating what and where to make cuts when you are dramatically reducing the size of a shrub.

Pruning outside and inside, top and bottom, carefully selecting what to remove and precisely where. I always look for an outward facing branch or leaf node so the next growth faces outside the shrub and toward the light.


Pruning Flowering Shrubs - Rutgers University
It's so important to cut at the right place and at the correct angle. A bunch of wrong cuts will leave you with a shrub that will not re-grow. Here's another chart that illustrates the best practises.

Stand back and look at the shrub frequently during the process. Walk away, get a drink of water, come back and reassess what you are doing. I never just keep cutting. I step back, walk away, look at it from a distance and then resume the shaping process.

Heading back cuts branches at a bud. Thinning removes an entire branch at its origin, whether that's  the ground or a larger branch. No matter what you've been told in the past, it is no longer considered wise to dress the cut surfaces with anything - sealer, paint.

Now sunlight can go into the center of
our Burford Holly shrubs to encourage
new growth inside.
If you are pruning a spring flowering shrub, remember 'prune after bloom' is usually safe, though there are exceptions. Spring flowering shrubs bloom on last year's growth so pruning early removes the flowers.

Summer flowering shrubs bloom on new growth so they are pruned now before spring growth has begun.

Summer-flowering shrubs (prune before spring growth begins)
Botanical NameCommon Name
Abeliaglossy abelia
Buddleiabutterfly bush
Callicarpabeautyberry
Caryopterisbluebeard
CeanothusJersey tea
Clethrasummersweet
Hibiscusrose of Sharon
Hydrangea macropyllabigleaf hydrangea
HypericumSt. Johnswort
Iteasweetspire
Potentillacinquefoil
Rhussumac
Rosa spp.rose
Spiraea x bumaldaWaterer spirea
Symphoricarpos/coralberry
Vitexchaste tree

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