I have noticed box blight affects the top part of hedges and topiary more than the base. The top is where the fungal infection seems to thrive, causing the most defoliation and stem damage.
My approach with box blight infections is to treat the hedge twice a year with a commercial grade fungicide and encourage the gardener or homeowner to adopt good gardening practices such as watering from the base, regularly sterilising clipping tools and clearing up as much fallen box leaf litter as possible.
So far this approach has had good success. The fungicide helps stop the infection getting worse and gives the box hedge a chance to recover. But unfortunately you can’t kill box blight. Once a hedge has become infected, it becomes a case of managing the disease rather than finding a cure. There is always a chance the infection will flare up again as fungal spores can remain active for up to 6 years.
The hedge in the photo above did recover. But as most of the damage from the blight infection was concentrated on the top, I was left with a hedge that had lovely new growth on the sides and twiggy patches along the top. So I cut the box hedge with a curved top using the fresh growth on the sides to hide the twiggy areas that were taking longer to recover.
This did improve the appearance and I also noticed the incidents of reinfection on the top were reduced. The repeated fungicide treatments were obviously a factor but it started me thinking whether cutting the box with a curved top was better for the health of the hedge?
Before I explain my reasoning I should add there is not scientific basis behind this theory! It’s based on my experience of working with box hedging and topiary.
A flat top is the popular choice for box hedging. This has be the same for centuries. Parterres and knot gardens created with box hedging used to be meticulously cut with flat tops using hand shears. Now we have the luxury of battery and petrol powered hedge trimmers that over time create a far tighter finish on the box than hand shears. This looks great but has the downside of reducing the air circulation into the hedge and creating conditions perfect for a fungus to thrive in. Cutting the box with a curved top improves the air flow into the hedge and discourages the box blight fungus.
The main difficultly with this approach is convincing the garden owners as most still prefer the look of a flat top. Changing the fashion to curved tops will take time. Personally I like the look of a curved top but it doesn’t work on all designs. The flat top suits formal parterre designs whereas curved tops work on more informal, organic designs like the snaking box hedge in the photos below. What do you think?