Fraxinus pennsylvanica 'Cimmaron'

Cimmaron Ash is a named cultivar of Fraxinus pennsylvanica, the North American Green Ash, chosen for its uniform symmetrical shape and its autumn colour. Where the ordinary species turns yellow, this selection colours orange to brick red. It is a deciduous shade tree used mainly in streets, car parks and public open space.

Yes. 'Cimmzam' is the registered cultivar name and Cimmaron is the trade name it is sold under, so Fraxinus pennsylvanica 'Cimmzam' and Cimmaron Ash are the same plant. You will also see it written Cimarron with a single m, which is a common misspelling rather than a different tree.

Autumn colour and crown shape. Cimmaron colours orange to brick red and holds a notably even, symmetrical crown, which is why it is specified for matched avenues and street rows. Claret Ash gives the deepest purple-burgundy autumn display and a broader crown. Golden Ash turns clear yellow and carries bright yellow stems through winter. All three are deciduous shade trees of a similar scale.

It reaches 12 to 15 metres tall with a canopy 8 to 12 metres wide at maturity. That takes several decades in most Australian conditions. It is a genuine shade tree, so it needs open ground and clear airspace, not a courtyard or a narrow verge under powerlines. Site it with the mature width in mind from the start.

Growth is moderate to fast, around 40 to 60 centimetres a year while the tree is establishing its framework, then slower as it matures. Regular deep watering and a good mulch ring through the first three summers make the biggest difference. On compacted or unimproved ground expect the lower end of that range until the roots spread.

An established tree handles moderate drought and the dry, reflected heat of paved surrounds, which is why it is a common street tree selection. It is not a dry country species though, and prolonged drought without any supplementary water shows up as early leaf drop. Young trees need consistent watering for the first two to three summers.

It is one of the standard choices for these situations. The symmetrical form means a planted row grows up matched, the trunk lifts to give vehicle and pedestrian clearance, and the tree tolerates compacted soil, pollution and reflected heat. Give each tree adequate soil volume and keep it well clear of underground services and building footings.

Colour comes on through April and May in most districts, later in warm coastal areas. The glossy green foliage moves through orange to a deep brick red and holds for a few weeks before dropping, staying on the tree later into winter than most other ash. Cool nights and a bright, dry autumn produce the strongest colour, while a mild humid autumn gives a shorter, softer display.

Water deeply through the first three summers, mulch widely and keep turf and weeds off the root zone while the tree establishes. Prune in late winter when the branch structure is exposed, removing crossing limbs and lifting the lower branches gradually to the clearance you want. Mature trees need little beyond deadwood removal and clearing the autumn leaf fall.