Pruning A Juniper Hedge

A friend asked me recently about pruning a juniper hedge I thought the exchange would be helpful to a wider audience, so our exchange is below:

Question:
I just bought a house that has a 40 foot long Juniper hedge along the driveway. It's healthy and has been trimmed regularly, but it's a 5' by 5' rectangular box. I'd like to trim it back at least a foot on the north side, where it's overgrown the driveway, and shape it so that it's more triangular... wider at the base, narrower at the top… When is the best time to trim them back? Can I do it this winter? How much can I safely trim back? Should I do the butchery myself, or hire a professional that knows what they're doing?

Response:
The short answer is that junipers aren't trivial to prune. But finding a professional who ‘knows what they’re doing’ isn’t trivial either

I’ll assume that you’re plant ID is accurate and I’ll do my best to give you a longer more constructive answer. There are entire books written to answer a question like this so I’ll only hit a few of the high points.

A hedge narrower at the top than at the bottom is actually healthier for the plant since it allows sunlight to reach all the leaf surfaces. But, make it more of a trapezoid than a triangle, flat or rounded on top. Or better, yet a shape nature intended.
Regular trimming is essential for a juniper because it doesn’t produce much new growth from old wood – this does make it difficult to cut back severely.

For a healthy shrub that responds well to pruning (not a juniper) the guideline is to never take more than 1/3 of the wood off in any one season. So I wouldn’t recommend cutting it back to 1 foot. You’ll need to do it gradually over many seasons. Also, you need to be prepared for it to look really ugly until it starts to recover and if it doesn’t recover be prepared to replace it.

The best way to prune a juniper is to grab the tip of a branch that is too long and follow it back to a connection to a larger branch or all the way to the base of the plant and cut it off there. This will give you a much more natural look and is healthier for the plant. I NEVER prune with hedge trimmers – use pruners or loppers. The best time to prune is in late winter – mid-Marchish, just before sugaring season, depending on the weather.

If you do decide to hire this out look for someone who is a Certified Landscape Professional (http://www.nhlaonline.org/certification/certified-professionals.cfm, http://www.melna.org/professional.html), they have demonstrated knowledge in many horticultural practices, including pruning. You could also look for a licensed arborist.
I hope that helps.

Happy Gardening,

Patty Laughlin, NHCLP, AOLCP

Owner/Head Gardener

Lorax Landscaping

Epping, NH