Jooni

An exemplary photo of a Pieris/ Andromeda bonsai

Pieris/ Andromeda

2 Species

Species

Pieris japonica Pieris japonica 'Forest Flame'

Pieris, also known as Japanese andromeda or lily-of-the-valley shrub (Pieris japonica), is an evergreen, acid-loving shrub with interest all year: glossy leaves, bright red to bronze new growth in spring, and drooping clusters of white or pink bell-shaped flowers from late winter into spring. A Pieris bonsai is an outdoor tree all year round; it is hardy to about -20°C (-4°F) in the ground and needs only root protection and shelter from drying winds in a hard winter.

Its needs for lime-free soil and rainwater, and its fairly slow growth, make it best suited to growers with some experience or careful beginners. Note that all parts of the plant are toxic to people and pets if eaten.

At a glance Pieris japonica

Difficulty
Intermediate
Placement
Outdoors
Light
Sun to partial shade
Watering
Moderate
Min. temperature
-10°C (14°F)
Foliage
Evergreen

Fertilizing

Feed your Pieris bonsai from the end of flowering until late summer, using an acid (ericaceous) fertilizer suitable for azaleas and rhododendrons. Apply organic fertilizer cakes every four weeks or liquid fertilizer every two weeks at the dose on the label.

  • Do not feed a freshly repotted tree for about four weeks.
  • If leaves turn yellow between green veins, add an iron supplement (chelated iron).
  • Stop feeding in autumn so the new growth can harden before winter.

Placement

Keep your Pieris bonsai outdoors year-round in a bright spot with morning sun and shade from the hot afternoon sun, which scorches the leaves. It prefers mild summers and suffers in strong heat, so a sheltered, airy spot with good air circulation is ideal.

The plant itself is very hardy, but roots in a pot need protection once temperatures fall below about -10°C (14°F). Move it to a cold frame, unheated shed or sheltered spot on the ground, out of drying winds and protected from late frosts that damage the flower buds and tender new shoots; never keep it in a heated room.

Pruning

Prune right after flowering, once the flowers have turned brown: remove the spent flower clusters and shorten shoots to shape the tree. Pieris forms next year's flower buds during summer, so finish pruning by early summer if you want flowers.

  • Pinch new shoots during the early years to build ramification and keep foliage dense.
  • Never strip all foliage from a branch, as this causes dieback; always leave some leaves.
  • Wire young shoots carefully and remove the wire after about three months, before it marks the bark.

Keeping the tree in a small pot and pinching regularly helps reduce leaf size.

Repotting

Repot every 2-4 years in spring, just after flowering, or in early spring if you are willing to lose that year's flowers. Trim about a quarter of the roots from the sides and bottom to keep the root system compact.

Use a lime-free, acidic soil (pH 4.5-5.5), such as kanuma or an azalea mix with some pumice, that drains well while staying moist. After repotting, keep the tree out of sun and wind for a few weeks and water consistently.

Watering

Keep the soil evenly moist but never waterlogged, and never let the root ball dry out completely. Underwatering quickly dries out the leaves, while constant wetness causes root rot.

Water with rainwater or other lime-free water whenever possible, as hard tap water gradually raises the soil pH and causes chlorosis. Watering needs increase in summer and after repotting, when the disturbed roots are more sensitive.

Seasonal care

  • Spring: The tree flowers from late winter into spring; remove spent flower clusters once they turn brown and protect the tender red new shoots from late frosts. Repot just after flowering if due, and start feeding with an acid fertilizer.
  • Summer: Give morning sun but shade from the hot afternoon sun, and water more often as the soil dries faster. Pinch new shoots to build ramification, but finish pruning by early summer because next year's flower buds form during summer.
  • Autumn: Stop feeding, leave the newly formed flower buds untouched and keep the soil slightly moist. Prepare winter protection before the first hard frosts.
  • Winter: Keep the tree outdoors and protect the roots once temperatures fall below -10°C (14°F), for example in a cold frame or unheated shed, out of drying winds. Water sparingly with rainwater, but never let the root ball dry out.

Common problems

Pieris is generally robust as long as its soil stays acidic and well drained, but a few problems come up regularly.

  • Yellowing leaves (chlorosis): Caused by hard, limy tap water or soil that has turned alkaline, which locks up iron. Water with rainwater, use a lime-free mix and feed with an acid fertilizer or an iron supplement.
  • Pale, mottled leaves: The typical sign of andromeda lace bug, which sucks sap from leaf undersides and leaves dark specks of excrement there; it is worst in hot, sunny spots. Inspect the undersides from late spring and treat with insecticidal soap or a suitable insecticide.
  • Root rot: Waterlogged soil encourages Phytophthora, causing wilting and branch dieback even when the soil is wet. Use a free-draining mix, keep the drainage holes clear and avoid overwatering.
  • Brown, scorched leaves: The result of intense afternoon sun, drying winter winds or a root ball that has dried out. Provide afternoon shade, shelter the tree from wind in winter and water consistently.