How do I garden in a wind tunnel between buildings?
Why a narrow gap between buildings accelerates wind rather than sheltering from it, what that does to plants, and how to break the flow without creating turbulence that is worse.
- Difficulty
- intermediate
- Time
- 40 min
- Read
- 4 min
Short answer
Wind squeezed through a gap speeds up, so the space between two buildings, along a passage or at the corner of a block can be substantially windier than the open ground either side. Solid barriers make it worse by creating turbulence and eddies downwind. What works is permeable filtering — mesh, slatted screens, hedges — plus low, tough, small-leaved planting and containers heavy enough not to move.
Urban and suburban gardens produce some of the windiest spots in the country, which surprises people who associate wind with open countryside. The mechanism is funnelling, and it is why a courtyard between two blocks can be unplantable while a field a mile away is fine.
Step by step
- Find where the acceleration actually happens.Tie ribbons or strips of plastic bag to canes at head height across the space and look at them on a windy day. You will usually find a narrow band of much stronger flow through the gap, with calmer eddies to either side.
- Understand why solid barriers fail.Wind hitting a solid fence or wall goes over the top and comes down hard on the other side, producing turbulence and often a windier spot a few metres downwind than there was before. It also concentrates pressure on the barrier itself.
- Filter rather than block.A screen that lets roughly half the wind through slows the flow smoothly and shelters ground for a surprising distance downwind — considerably further than the height of the barrier. Slatted panels with gaps, woven willow or hazel, and mesh all do it.
- Use planting as the permanent filter.A hedge or a row of tough shrubs is the best permeable windbreak there is: it filters, it does not create turbulence, and it improves rather than degrades. It needs establishing behind temporary shelter on a really exposed site.
- Choose plants built for it.Small, tough, narrow or divided leaves; flexible stems; low growth; a willingness to be battered. Large soft leaves shred, tall thin stems snap, and anything that needs still air to set fruit will struggle.
- Plant low and let it thicken.In a wind tunnel, low planting sits in the slower boundary layer near the ground. Tall specimens stand up in the fastest flow, need staking permanently, and rock.
- Deal with containers properly.Wind-tunnel gardens are usually paved, and pots blow over. Use heavy pots, plant low, group them, and secure anything tall.
- Expect to water more.Wind is a drying force. Constant airflow across foliage removes moisture far faster than still air, which is why plants in a windy site need more water than the rainfall suggests.
Tips
- A permeable barrier shelters ground for a distance of several times its own height downwind. That means a modest screen protects far more than people expect, and a tall solid one protects less than they expect.
- Corners of buildings produce the strongest local acceleration. If one corner of the garden is unplantable, look at what is happening upwind of it.
- Wind chill and desiccation do more damage in this situation than physical breakage. Evergreens browning on the windward side are the classic symptom.
- Trellis with a climber on it becomes a solid barrier once the climber fills it. If you want a filter, choose an open climber or accept that the panel will behave as a wall.
- Anything you build has to be engineered for the loads. A screen in a funnelled site takes far more wind pressure than the same screen elsewhere, and cheap panels fail.
Common mistakes
- Putting up a solid fence or a close-boarded panel to block the wind — It creates turbulence downwind that is often worse than the original flow, and in a funnelled position it takes the full pressure and blows down.
- Planting large-leaved or tall specimens in the funnel — They shred and snap, need permanent staking and rock in the ground. Low, small-leaved and tough is the planting palette a funnelled site allows.
- Assuming a sheltered-feeling courtyard is sheltered — Enclosed spaces with gaps at either end are among the windiest positions there are. Test it with ribbons rather than judging by how enclosed it looks.
Questions people ask
Would a solid wall work if I made it tall enough?
No — height makes the downwind turbulence worse rather than better. The principle is filtering, not blocking, and it holds at every scale.
Can I grow anything tall at all?
Yes, once you have established shelter and if you choose flexible, small-leaved species and stake them low for their first years. Building the shelter first and planting into it is the order that works.
Does this apply to balconies and roof terraces?
Very much so, and more severely — wind speed increases with height, and the edges and corners of a building produce strong local acceleration. Permeable screening, low tough planting and secured heavy containers are the same answers.