Strange wind tunnel effects

Loxley · August 2021

I have a high fence along the North East boundary of my garden, facing south west. The wind must get trapped by the buildings and fencing, because tall plants tend to lean away from the fence, and stuff at the back of the bed ends up almost flattened, showing that the wind funnels along the base of the wall in the direction of the arrows on the Google maps image. (North is up).

It's not a disaster, but I wonder if anyone else had noticed anything similar and managed to deal with it? I'm thinking of planting a couple of larger shrubs or small trees to bear the brunt of the wind, and had already decided to edit out a lot of taller perennials.

BenCotto · August 2021

I have heard of scaffolding debris netting being used as a garden windbreak. It won’t be elegant but it will be inexpensive and almost instantaneous.

Loxley · August 2021

I think I'd rather have flattened plants than a scaffold net, but the idea of some sort of pergola did occur to me, to absorb some of the force.

BenCotto · August 2021

Loxley said:

I think I'd rather have flattened plants than a scaffold net,

Don’t blame you. Me too.

Nanny Beach · August 2021

We have similar but the whole garden,back faces north.we are 10 minutes from the sea,in the next road to the south downs,wind come from that side which is our west. You can walk one road away,and there's no wind. It's flaming annoying.Taller plants are in front of fence mostly on the east side,a lot of staking involved.

Fairygirl · August 2021

I had the same at a previous house once we extended it. It was down the side of the house, and I planted some shrubs at the front boundary to filter it, and also had all my compost bins etc down that side, which helped. By the time it reached the back garden, where there was more planting, it had done the job.
Other than that, using shrubs to help support perennials is the best method.
A basic shelter belt of shrubs/trees is always necessary in any windy site, but careful placement is important, and you often need to have enough room to do it for it be effective. It's regularly very windy here, so anything light weight needs support or protection, or sometimes both. Even with that screening, it can be tricky.

jonathan.cole · August 2021

@BenCotto is right. With wind, porous objects (like hedges, scaffold netting or wind break netting) filter the wind whereas solid objects redirect it. That redirection causes turbulence.

It's been a very long time since I did anything with fluid dynamics, so take my comments with a large pinch of salt.

What I *think* is happening is that the W or WSW wind (which I am guessing is your main wind direction) is hitting the house side and causing a down-draught which then spirals out sideways along the beds in a vortex (figure 1).

To reduce the down-draught you can slow the wind with a tall wind break (most likely a tree), either by the fence near the house (figure 3) or at the windward end of the garden (figure 2). These will obviously take some time. This will obviously take time to grow. Mitigating the down-draught might be possible with some hedging against the fence and as other people have said anything decently shrubby will help slow the wind in the vortex.

You could probably build a pergola type structure above the windy bed that would block most of the down-draught, so long as the roof was slatted in a way that didn't block the westerly wind otherwise you'd just create more turbulence again (figure 4, if my dodgy sketch helps at all).

You can test the impact of things with some plastic windbreak fence on suitable canes etc. that you can move around to try different positions.

Loxley · August 2021

Thank you Jonathan, I really appreciate it. I was thinking of planting a couple of specimen Amelanchiers (or similar) in positions A and B so hopefully they will help. The red arrows are where I guess the downdraft is coming from (the neighbour's flat car port probably is adding to the issue!) The thick blue line is the area where the wind shuttles across the bottom of the wall, currently almost flattening my Aster. I might plant the base of the wall with something more resilient like Rosa pimpinellifolia instead.

Image: https://us.v-cdn.net/6030279/uploads/editor/4v/wp0kndaumupo.jpg

Loxley · August 2021

In fact I know it blows a hoolie over the top of that fence under the carport, the upper wire holding the clematis strains with the wind sometimes. Think the carport might gather the wind and then it escapes through that gap. The carport is in the gap between my end terrace and the neighbour's detached house.

jonathan.cole · August 2021

There's a lot there to redirect the wind, no wonder it's doing weird things!

Looking at your arrows I wonder if a chunk of the down-draught is coming from your house as well?

I'd expect the amelanchiers to help, but it's worth spending some time on a windy day observing what the wind is up to as well and thinking about how to slow it.

Good luck!

raisingirl · August 2021

Don't disagree with anything JC has said but just to add, some plants do lean away from a wall which may be exacerbating the issue.
I guess there's a reason you don't have plants overtopping the fence, but you would find something semi-permeable along there (trellis between the top of the fence and the underside of the car port?) would possibly dissipate the strongest effects. If you are getting a down-draught from your house wall, then a sturdy climber over that wall would help to slow it down and filter it. You do have to find something that will cope with bearing the brunt of it for that to work though.

Strange wind tunnel effects

Posts