Flowering Dogwood ‘Rainbow’ · Cornus florida ‘Rainbow’

Cornus florida 'Rainbow' is a slow-growing deciduous small tree reaching 4 to 6 metres in height, forming a low-branching rounded crown of horizontal tiered habit. The cultivar is distinguished by its variegated foliage: leaves carry a broad cream to yellow marginal band against a green centre across the full growing season, then turn deep red to purple in autumn. White bracts surrounding the true flowers open in April and May, producing a four-bract display at branch tips.

The species is cold-tolerant to well below minus 20 degrees Celsius in its native eastern North American range, but performance in Germany is limited not by absolute winter minima but by late spring frosts and incomplete wood ripening in cool summers. Reliable ornamental performance is therefore confined to the milder Klimaregionen: the Oberrheingraben (Upper Rhine valley), the Niederrheinische Bucht (Lower Rhine basin), and the Cologne lowland. The tree is marginal east of the Elbe and above 400 metres in the voralpenland (pre-Alpine foothills), where late frosts damage the opening bracts. Site away from frost pockets and provide a windbreak on exposed positions.

Standortansprüche (site requirements) are exacting. The species demands moist, fertile, slightly acidic to neutral loam with reliable drainage, and tolerates neither strongly calcareous substrates above pH 7 nor compacted urban soils. Mulch retention through the first three summers is essential, since the shallow root system desiccates rapidly under direct sun on free-draining sand. Partial shade is preferable on southern exposures; full sun is acceptable only where summer soil moisture is secure.

Disease pressure governs specification. Cornus florida is the principal host of dogwood anthracnose (Discula destructiva) and is also susceptible to powdery mildew, spot anthracnose, and crown canker; reserve the tree for individual planting positions where stress factors can be managed. This is not a candidate for Stadtbaumeignung (street tree suitability): salt tolerance and compaction tolerance are both low, and the cultivar carries no entry on the GALK-Straßenbaumliste. Its legitimate role is as an isolated specimen in a Kurpark, residential garden, or sheltered Landschaftspark margin, where the variegated foliage and spring bract display carry the design.