Juniper procumbens 'Nana'

Juniperus procumbens 'Nana' is probably the most commonly sold bonsai in the world. Most garden centre "starter" bonsai are this species, and most of them die within a year because they're sold with the label "indoor bonsai" when in fact they're emphatically not.

Kept outdoors year-round in full sun, given a free-draining substrate and watered when the soil starts to dry, J. procumbens is one of the easier species in cultivation. It tolerates cold well, doesn't mind dry air, recovers from pruning, and wires beautifully into the cascading, windswept and informal styles it suits naturally. Kept on a windowsill, it slowly browns from the inside out and dies over six to eighteen months. The single biggest favour you can do a juniper is to put it outside and leave it there.

Junipers want to dry slightly between waterings — not completely, but the surface should feel dry before you water again. In most UK summers this means every 1–2 days; in winter, every 3–5 days. Overwatering is the more common killer than underwatering: roots in saturated, cold substrate rot fast, and root problems on a juniper aren't visible above ground until the foliage starts greying out, by which point it's usually too late.

When you do water, water thoroughly — until it runs from the drainage holes. Light, frequent watering keeps only the top of the substrate wet and encourages shallow rooting.

Junipers tolerate hard tap water without complaint.

Feed lightly. Liquid feed every two weeks during the growing season (May–September) at half strength. Slow-release organic pellets in spring and early summer. Stop feeding by mid-September.

Junipers respond more to consistent light feeding than to heavy doses; an overfed juniper produces coarse, juvenile-looking needle foliage instead of the refined scale foliage you want.

Very free-draining is the priority. Junipers tolerate poor substrates better than they tolerate wet feet.

Repot every 3–5 years. The window is later than for deciduous trees — wait for clear signs of root activity (new white root tips visible at the drainage holes, or new shoot extension above) before disturbing the roots. In the UK this typically means late March to mid-April for the south; April through to early May further north.

Junipers don't tolerate aggressive root pruning. Remove no more than a quarter of the root mass on healthy trees; less on older or weaker specimens. Don't bare-root a juniper — leave the inner core of the root ball undisturbed and work only the outer roots.

Keep the freshly repotted tree out of strong sun and wind for at least three weeks afterwards.

Junipers are pinched, not cut. Pinch out the soft growing tips through the growing season — June through August — using your fingers (clean nails, no scissors on foliage; scissors brown the tips). Pinch each shoot back to where you want growth to extend from. Don't pinch the whole tree at once — work in waves through the season so the tree always has some active growth driving sap flow.

Major branch removal happens in late winter or early spring, before new growth begins. Cuts heal slowly on junipers — leave deadwood (jin and shari) where you can rather than cutting flush, since deadwood is a feature of the species.

A common beginner mistake: heavy scissor-cutting through the foliage pad. This browns every cut tip and the tree looks scorched for months. Use fingertips on green growth, scissors only on woody branches.

Wiring is fundamental to juniper styling and the species takes wire very well. Apply in late summer (August–September) for shaping completed through winter, or in winter on dormant trees. The bark is reasonably forgiving but wire can still mark if left too long — check every couple of months and remove before it bites in.

Junipers will hold a position better than most species — wired branches retained for 6–12 months will usually stay in place after the wire comes off.

Informal upright, cascade, semi-cascade, windswept, literati, root-over-rock. Junipers suit dramatic, asymmetric styles and benefit enormously from deadwood features — jin (stripped dead branches) and shari (stripped trunk areas) make a juniper read as ancient and weather-beaten. Most refined juniper bonsai feature substantial deadwood.

Avoid formal upright (chokkan) and broom (hokidachi) — they don't suit the species' natural growth habit.

Properly hardy in the UK with minimal protection. Down to -10°C they need no help at all if grown outdoors in a normal pot. In a hard freeze (below -10°C sustained for several days, rare in most of the UK), shelter from wind helps.

The bigger winter risk is sudden temperature swings on south-facing benches — a sunny February day can warm a pot enough to start sap flow, and a hard freeze that night damages the partially-active roots. A position that gets winter morning sun rather than afternoon sun is ideal.

Never bring a juniper indoors. Even for a few weeks. Even "just over Christmas". Junipers need cold dormancy and the indoor environment is fatally dry for them.

From semi-hardwood cuttings in late summer (August–September) — very high success rate, the standard propagation method. Air layering is possible but slow. Junipers are rarely grown from seed for bonsai because seedlings produce juvenile needle foliage for years before maturing to scale foliage.

Junipers are generally healthy outdoors but have a few specific problems worth knowing. The species' biggest enemies are not pests but watering errors and the wrong location.