Size is mostly set by the roots
Rootstocks
If you want a reliable crop, the RHS says, it’s worth investing in a good-quality grafted tree of your chosen variety, bought from a reputable supplier. RHS Cherry trees sold commercially are usually grafted onto the roots (rootstock) of a different variety that controls the tree’s size and vigour, the RHS says. Ungrafted cherries grow into large trees that aren’t suitable for smaller gardens. RHS
Many fruit trees are grafted onto rootstocks, the RHS says. These rootstocks control the vigour of the plant, allowing the cultivation of trees in a smaller space than if they were grown on their own roots. Rootstocks can also improve disease resistance. RHS For cherries, that page lists the rootstocks Gisela 5 or G5, described as semi-dwarfing, and Colt, described as semi-vigorous. RHS
The most popular cherry rootstocks, the grow guide says, include ‘Gisela 5’, a semi-dwarfing rootstock that restricts trees to 3–4m (10–13ft) tall, so suitable for smaller gardens and containers. RHS Trees trained as fans on ‘Gisela 5’, that page says, will reach about 1.8m (6ft) tall and 3.5m (12ft) wide. RHS
On the rootstocks page, Gisela 5 or G5 is described as semi-dwarfing, suitable for bush, pyramid and fan, starting to fruit in three or four years, with an ultimate height as trained as a bush of 2.4-3m (8-10ft). Staking is permanent; spacing 2.7m (9ft). RHS
How tall is a tree on Gisela 5?
The RHS grow-your-own cherries page says ‘Gisela 5’ restricts trees to 3–4m (10–13ft) tall. The RHS rootstocks page gives an ultimate height, as trained as a bush, of 2.4-3m (8-10ft). Both figures stay in view. Fan-trained sizes on the grow page are listed separately.
‘Colt’ is a semi-vigorous rootstock, the same guide says, producing trees 6–8m (20–26ft) tall, or when fan trained 2.5m (8ft) tall and 5.5m (18ft) wide. RHS Acid cherry trees, which are less vigorous, reach about 3.5m (11ft) on ‘Colt’, the RHS says. RHS
Colt is described there as semi-vigorous, suitable for bush, half standard and fans, starting to fruit after three or four years, with an ultimate height as trained as a bush of 6m (20ft). Many soils are tolerated, including clay and light, chalky soils. Staking is permanent; spacing 6m (20ft). RHS
How tall is a tree on Colt?
The RHS grow-your-own page says ‘Colt’ produces trees 6–8m (20–26ft) tall, or 2.5m by 5.5m when fan trained, with acid cherries reaching about 3.5m on this rootstock. The rootstocks page gives an ultimate height, as trained as a bush, of 6m (20ft). The “as a bush” figure and the wider 6–8m range are not identical, so both stay in view.
Eleven metres, or a rootstock tree?
Britannica says sweet cherry trees are large and rather upright, attaining heights up to 11 metres (36 feet). The RHS says ungrafted cherries grow into large trees that aren’t suitable for smaller gardens, and that commercial trees are usually grafted onto a rootstock that controls size — ‘Gisela 5’ or ‘Colt’, at a few metres, not eleven. The 11-metre figure describes the species; garden trees on a rootstock are kept much smaller.