How to trim large (forsytha) hedge

(Question)

My husband and I recently purchased a 19th century, Toronto-area farmhouse, including a hedge that may be almost as old.

The property is generally in need of updating, and there has been little, in the way of proper landscaping. I’m systematically changing that. The forsythia hedge, in particular, is gloriously approx. 50′ in length, 7′ high, and 5-6′ deep. It is full, healthy, and decades out of by-law compliance. And therein lies the problem.

I need to trim the height (and may even consider trimming the depth, at some point), but I’m all of 161cm, myself. And the 50′ length doesn’t lend itself very well to taught string lines. (I’m wondering if a board laid on the top of the hedge, with a level, might be a better plan? You know…cut the initial section to the desired height, then move the board and level along, as I go?)

You’d think my just-under-seven-feet-tall hubby would be the natural choice to tackle this job. But you’d have to think again. So, it’s up to shrimpy me. In fact, the hedge is so deep, once on a ladder, at the top of the hedge, I can’t even sufficiently reach across the entire width of the hedge, necessitating another pass on the other side, to trim the top, on that side.

I’ve been satisfied with the trimming I’ve done at past properties, on reasonably-sized yews and euonymous, by eyeballing the task, and using an electric hedge trimmer. But this stand-alone hedge on the front of the property is more of a challenge for me. I can’t afford to make any big mistakes.

I plan to trim it down to 5′-ish after next spring’s flowering (as per information found on the Internet about the best time to trim forsythia, unless you advise otherwise). At that point, I may opt to trim-back the depth, as well, as it may then be deeper than it is tall…which may look odd.

Very practically, any experience with getting a nice, flat, level top on such a tall, long, deep forsythia hedge? I’m stymied as to how to even begin, short of the ladder plus ‘board and level’ theory.

Any additional information or cautions would be appreciated, as well. :) At the very least, I don’t want to damage this established hedge.

(Answer)

Your new property sounds fabulous, but owning a century farmhouse myself, I know how much work can be involved maintaining the building and the landscape. And this forsythia hedge  sounds wonderful but does present a challenge. You mentioned that the old forsythia is in good shape, so we will assume that it only needs trimming to reduce the size, and not to re-stimulate blooming. The information that you found on pruning the forsythia after it blooms is correct as it flowers on old wood.

The only way I know to ensure a straight line for a formal hedge to use a string guide, even if the hedge is tall. When the hedge is long you just use multiple stakes along the 50 foot length, or prepare a shorter guide and prune the hedge in sections. The tool made for pruning tall plant material is a gas-powered, long reach pole hedge pruner which allows for the lengthy reach you need for the task. These can be purchased or rented, if you have your mind set on doing this job yourself. That said, there are some gardening chores that are often better and safer left to reputable professionals, as they have the tools and the know how. It may end up being cheaper, than purchasing the equipment yourself.

Here are a couple of great sites on pruning hedges if you decide to do it yourself:

https://www.finegardening.com/how-to/articles/trimming-hedge.aspx

https://www.bbc.co.uk/gardening/basics/techniques/pruning_prunehedges1.shtml

I hope that you will enjoy your property and its landscape for many years to come.