Chinese elm

If a friend asks which bonsai they should start with, Chinese elm is the right answer. It tolerates over- and under-watering, recovers fast from pruning errors, back-buds reliably on old wood, and develops a beautiful flaky bark surprisingly quickly. It works outdoors year-round in most of the UK, and unlike most outdoor species it will also tolerate spells indoors — useful if you're new and not yet confident with winter protection.

The trade-off is that it isn't the most refined or revered species in bonsai. A great Japanese maple is a great Japanese maple; a great Chinese elm is a great Chinese elm. But it's the species that teaches you most quickly what it feels like when a tree is happy.

Chinese elms are thirsty but tolerant. Water when the surface of the soil starts to dry — typically daily in spring and autumn, twice a day in high summer. Unlike maples they shrug off occasional dryness and recover well from a missed day, but consistent dryness causes leaves to crisp and drop.

They also tolerate slightly wetter feet than most deciduous species, which makes them forgiving of the inconsistent watering most beginners do. Don't take this as licence to leave them sitting in waterlogged soil — they'll still rot eventually — but a soaked pot after heavy rain isn't a crisis.

Tap water is fine. Rainwater is better. Either works.

Feed weekly with a balanced liquid feed from when leaves harden in spring (April) through to early autumn (mid-September). Chinese elms grow fast and will respond visibly to feeding — a well-fed tree pushes long extensions that you'll need to manage with regular pinching. An underfed elm sits and sulks.

Slow-release organic pellets (biogold or similar) work well alongside liquid feed; apply spring and early summer.

Reduce nitrogen from late August so the wood ripens before the cold. A high-K feed for a few weeks before dormancy helps hardiness.

Free-draining, moisture-retentive, slightly acidic to neutral. Chinese elms are less fussy than maples about substrate and will perform well in a fairly broad range of mixes.

Repot every 2 years for young trees, every 3 years for mature ones. The window is wider than for maples: late February through to mid-April depending on region. The ideal moment is just as buds begin to break.

Chinese elms tolerate aggressive root work — you can safely remove up to half the root mass on healthy trees. Comb the roots out radially, prune cleanly, and re-pot into fresh substrate. Water in heavily and keep out of strong sun for two weeks afterwards.

This is where Chinese elms shine. They back-bud reliably on old wood, tolerate hard cutbacks, and develop ramification quickly.

Structural pruning in late winter (February). Through the growing season, let new shoots extend to 6–8 leaves, then cut back to 1–2 leaves. Trees in development can be allowed to run further. Trees being refined need constant pinching from May through September — every two to three weeks in vigorous growth.

Don't be precious about hard pruning. An elm that's been cut back to bare wood will push new buds within weeks if it's healthy. This is the species to learn pruning on.

Wire after leaves harden in early summer, or on bare branches in winter. The bark thickens and develops character with age, but it doesn't mark as easily as maple bark — wire bites are less of a crisis. Standard anodised aluminium for most branches; copper for thicker structural work.

Watch growing branches closely — elms thicken fast in summer and a wire applied in June can cut in by August.

Almost any style works. Informal upright is most common, but Chinese elms make excellent broom-style trees (the natural habit of the species in the open), and they're widely used for clump and forest plantings because of how readily they back-bud. Their tolerance of hard pruning means you can radically restyle an existing tree without killing it — useful if you've bought commercial nursery stock that needs rethinking.

Hardier than they look but with a caveat: trees grown from indoor or greenhouse stock (most imported Chinese elms sold in the UK) haven't developed full winter hardiness and need more protection than the species technically requires.

For a tree that's spent its life outdoors in the UK, no protection is needed down to about -3°C. Below that, shelter from wind. Below -7°C, into an unheated greenhouse or cold frame.

For a newly imported tree, treat it as half-hardy in its first winter — keep it in a frost-free but cool space (a porch, an unheated conservatory) and acclimatise it gradually over a year or two of full outdoor seasons.

A common mistake is to keep a Chinese elm indoors permanently because the garden centre tag said "indoor bonsai". This is the species that started that confusion. It will survive indoors for a year or two but will be permanently weakened — it needs a proper dormant period to thrive long-term.

Easy from semi-hardwood cuttings in early summer (June) with rooting hormone — high success rate. Also from seed if you can find it, though cultivar names won't come true. Air layering works well in May–June.

Generally trouble-free. The species' Dutch elm disease resistance is a major advantage; most ailments are minor and recover quickly.