Zelkova forest planting: spacing five trunks on a 42 cm slab

A forest planting is read as a piece of landscape, not as five trees. Almost all of the work is in the spacing, the height ratios and the single empty space you leave open. This record covers how the group was laid out, why one trunk is deliberately thinner, and how the planting is rotated twice a year to keep the roots balanced.

Sourcing trees that will match

All five trunks came from the same batch of two-year-old zelkova seedlings, cut back to 12 cm in their first spring so they would throw a broom of shoots from one point. Matching provenance matters more than matching size: seedlings from the same batch grow at similar rates, so the group stays in proportion for years instead of one tree running away. At planting in 2017 the trunks were 1.8, 1.6, 1.5, 1.2 and 1.0 cm in diameter, and heights were set at 54, 46, 41, 33 and 28 cm.

The layout: heights, spacing and the gap

The tallest trunk sits about 14 cm from the left end of the pot, leaning very slightly left. The second tallest stands 9 cm to its right and slightly behind, which creates the depth that a flat row of trees never has. The remaining three are grouped to the right, with the shortest placed nearest the front so the eye passes over it. Total canopy spread is 38 cm on a 42 cm pot. The critical decision was leaving the right-hand 11 cm of the pot almost empty — the open ground is what makes the trunks read as a forest rather than as a hedge.

The deliberately thin trunk

The 1.0 cm trunk is not an oversight. A group where every trunk is a similar weight looks manufactured. The thin one sits at the far right, angled slightly away, and gives the composition a sense of continuing past the edge of the pot. It is also the tree that will be allowed to grow relatively freely for the next few seasons, while the dominant trunk is pinched hard, so that the ratio between them widens rather than closes.

Broom structure by pinching, not cutting

Zelkova builds a broom head by repeated division. From mid May, shoots on the main framework are pinched when they reach five leaves, back to two. From mid July the same shoots are pinched again at three leaves, back to one. Repeated over six seasons this turns each primary branch into a fan of fine twigs with no wire needed — the only wire on this planting is 1.5 mm on the dominant trunk, applied once in June 2020 to correct a 5 degree lean. Any shoot growing straight up from a branch crotch is removed entirely, because it will thicken the branch out of proportion.

Watering a 5 cm deep pot, and rotating the group

The soil volume in this planting is small enough that it can dry out in a single hot afternoon. From May to September it is watered twice a day, morning and early evening, and it is checked at midday on any day forecast above 30 C. In winter it is watered about every fourth day, and the whole pot is covered with a 15 cm mulch of dry leaves to stop the shallow root mass freeze-drying. The planting is rotated 180 degrees in April and again in September: without the rotation the trees on the shaded side lose vigour and within three years the group reads lopsided.