Aeonium arboreum 'Zwartkop'
Aeonium arboreum 'Zwartkop is a striking, tree-like succulent cultivar prized for its large rosettes of glossy leaves that deepen from green to a near-black burgundy in strong sun. Selected from the branching species Aeonium arboreum, it is one of the most widely grown and recognisable of all aeoniums. The cultivar name is Dutch for "black head"; the plant is also widely known as the black rose and is sometimes sold under the German form of the name, Schwarzkopf.
Care follows that of the parent species, Aeonium arboreum; the notes below cover only what sets the cultivar apart.
Description
'Zwartkop' forms an upright, branching subshrub with bare, woody stems topped by spoon-shaped rosettes that can reach 15–20 cm across on established plants. The leaves are smooth, slightly glossy and edged with fine translucent lashes typical of the genus. Colour is the whole point of this cultivar: in bright light the rosettes turn a deep chocolate-to-blackish maroon, usually retaining a greener heart around the growing point where the newest leaves emerge. In shade or during the growing season the same rosettes revert toward green, so the famous near-black tone is very much a response to light and stress rather than a fixed pigment.
Like most aeoniums it is winter-growing and tends to rest through the heat of summer, when lower leaves may shed and the rosettes close up tighter. Small yellow, star-shaped flowers appear in conical clusters on mature rosettes; as with all Aeonium, a rosette that flowers is monocarpic and dies after blooming, though the branching habit means the rest of the plant carries on.
Cultivation
Grow 'Zwartkop' as for Aeonium arboreum: a free-draining but not purely mineral mix (aeoniums appreciate a little more organic matter and moisture than desert cacti), bright light, and water during the cool growing months while easing off in hot, dry summer dormancy. See Watering and Repotting for general technique.
The one point that matters specifically for this cultivar is light. The dark colour only develops under strong, direct sun; in low light the rosettes stay green, stretch, and lose their compact form. Give it the brightest spot you can — a sunny windowsill, or outdoors in mild climates — but introduce full sun gradually, as the dark leaves can scorch if moved abruptly from shade. It is not reliably frost-hardy and is best kept above freezing.
Propagation
'Zwartkop' is propagated vegetatively to keep it true to type, since seedlings will not reliably come out dark. The easiest method is stem cuttings: remove a rosette on a length of stem, let the cut end callus for a few days, then root it in a gritty, barely-moist mix during the growing season. Branches and offsets root readily this way. See Propagation — cuttings for a full walkthrough.
Common problems
- Green rosettes / etiolation — too little light; the plant loses its dark colour, stretches, and the rosettes open up and become leggy. Move it somewhere much brighter.
- Summer leaf drop — usually normal dormancy behaviour rather than a fault; the plant sheds lower leaves and rests. Keep it on the dry side and it will flush again as temperatures cool.
- Rot — from waterlogged soil, especially if watered heavily during hot summer dormancy. Use a free-draining mix and let the soil dry between waterings.
- Pests — mealybugs (white fluff tucked into the rosette and leaf axils) and aphids on flower stalks are the most common; see Pests and diseases.
See also
- Aeonium arboreum — the parent species
- Aeonium — the genus overview
- Propagation — cuttings · Soil and potting mix · Watering · Repotting