A year of native bonsai on a narrow balcony in south-west London
A balcony is a strange place to grow trees, and a small one is stranger still. After six years on a narrow ledge in Twickenham, this is my attempt to set down what the space has asked of the trees, and of me, through a whole year.
Written 16 August 2026 · looked at again 13 September 2026 · 8 minute read
The space itself
The balcony is on the third floor, about four metres long and a little over a metre deep, facing south-west across a row of back gardens towards the river. It gets no direct sun until late morning and then a great deal of it through the afternoon, much of it reflected off the pale brick wall behind. It also catches every westerly that comes up the valley. The combination is harsh in summer and surprisingly mild in winter, when the wall gives back some of the day's warmth at night.
Most of the trees sit on two long slatted shelves along the railing side, at about waist and knee height, with the larger hawthorns on the floor in the corner that gets most shelter. Nothing sits on the balcony rail itself. Quite apart from the risk to the tree, a pot falling three floors onto a path is not a risk I am willing to take, and the building's managing agent was clear about that when I asked, as I would advise anyone to do before putting anything heavy outside.
Space is the constant limit. I have room for about twenty trees if I am careful, and part of the discipline of balcony growing is deciding what not to grow. Each spring I pass on one or two trees that are not developing well to friends with gardens, where they can grow out as ordinary shrubs. It felt like a failure the first time I did it. By the third year it felt like part of the work.
Summer: water, and wind
In July and August water is the only thing I really think about. A small bonsai pot in full afternoon sun and a steady breeze can go from wet to bone dry in a few hours, and a native deciduous tree that dries out completely in summer will drop its leaves within a day and may not recover. On the hottest days I water early in the morning, check again at lunchtime if I am home, and water again in the early evening, soaking each pot until it drains freely.
When I am out all day, the smallest trees go into shallow trays of grit that I flood in the morning, so that they can draw water up through the drainage holes. It is not ideal for the roots, and I only do it on the hottest days, but it has saved more than one tree in a heatwave. For longer absences a neighbour two doors along does the watering, following a laminated card clipped to the shelf that shows which pots need what, and I return the favour with her tomatoes.
Wind is the other summer problem, less dramatic than drought but steadier. It dries the leaves at their edges and scorches the soft new growth on the most exposed trees, particularly the field maples, whose leaves are thinner than those of the hawthorn. A length of green windbreak mesh along the railing, fixed with cable ties at the height of the shelves, cut the worst of it by half and still lets through enough air to keep mildew down.
On the potting bench
- Water in the morning and the early evening, more in a heatwave
- Soak each pot until water drains freely from the bottom
- Shallow grit trays for the smallest pots on long days out
- Windbreak mesh along the railing at shelf height
Winter: letting the trees be cold
The most common question from visitors is whether I bring the trees in for winter. The answer is no. Hawthorn, field maple, blackthorn and hornbeam are native trees that need a proper cold period to go dormant and then to break bud properly in spring. Brought into a warm flat, they would start growing in January, produce weak, pale shoots in poor light, and fail. They need the cold far more than they need protecting from it.
What they do need protecting from is freezing solid in their pots. In the ground, roots are insulated by the soil around them. In a small pot on a balcony, a hard frost can freeze the whole root ball through, and repeated freezing and thawing can kill the fine roots. When the forecast drops below about minus three, I move the trees off the shelves and down against the wall of the flat, grouping the pots closely and packing the gaps with bubble wrap and old fleece.
In six winters I have had to do that perhaps a dozen times, and I lost one small blackthorn in a cold spell in 2022 after leaving it on the top shelf through one careless evening. The larger trees, with more soil around their roots, have never shown any damage. The wall does much of the work. London balconies are milder than most gardens outside the city, but milder is not the same as safe, and a clear, still night in January can still catch you out.
Living with neighbours, and the flat below
A balcony garden exists at very close quarters with other people's lives, and I have come to think that keeping the neighbours content is as much part of the practice as watering. The most important thing is where the water goes. Every shelf has a drip tray beneath it, and I water slowly enough that nothing runs off the edge onto the balcony below. The downstairs neighbour has a small table out there and a reasonable wish to keep her tea dry.
The same goes for mess. Repotting sheds soil and grit everywhere, so it happens on a tarpaulin that folds up afterwards, and prunings and old soil go into a bag rather than over the side. Leaves in autumn are swept every few days, partly to keep the drains clear and partly because a pile of wet hornbeam leaves blocking a shared drainpipe is exactly the sort of thing that gets mentioned at a residents' meeting.
The trees have also given me a reason to talk to people I would otherwise only nod to on the stairs. The neighbour with the tomatoes now has a small field maple of her own, grown from a seedling I found in one of my pots, and the couple on the top floor ask every spring when the hawthorn will flower. It usually does in May, briefly and heavily, and for about ten days that corner of the building smells faintly of the hedge it came from.
On the potting bench
- Drip trays under every shelf
- Water slowly, so nothing runs over the edge
- Repot on a tarpaulin, and bag the prunings
- Sweep up leaves before they reach the shared drains
Written on a south-west facing balcony in Twickenham, south-west London. What works here may need adjusting for a colder garden or a shadier ledge.