Alnus cordata
Italian Alder is a stately conical-shaped tree that has naturalised in many parts of the UK. A very robust tree that can grow to 24 meters tall, it is often found growing in city parks and avenues as it can cope with urban conditions and pollution. The Italian Alder’s leaves are glossy green, and it has an attractive cone-like fruit.
Styles & Sizes: It makes handsome Medium to Large Bonsai, in most upright styles.
Position: The Alders love a Sunny position though it can take a partially shaded position too. In summer protect from drying out by placing in a humidity tray. In winter protect Alnus in a greenhouse as they don’t like their roots frozen.
Watering: Water thoroughly early in the morning especially in the summer as the Alder like moist soil and do not like to dry out at all.
Feeding: Feed with a balanced organic fertiliser. Organic manure, release its nutrients slowly ensuring that leaf sizes and internode distances stay small and controlled. If using a liquid fertiliser feed every two weeks, if feeding with a pelleted version feed when feed dissolves away.
Repotting: The Alders roots grow very quickly and massively so younger bonsai need to be root pruned every year. They like a water-retentive growing medium so use a blend of loam, well-mulched bark, sharp sand, in equal parts. Alternatively, you can use a mix of Akadama, Pumice and Well Mulched Bark in equal parts. Ensure that all the fines are removed in both mixtures.
Pruning: After the current year's extension have fully extended prune back to leave 3 active leaf nodes or lateral shoots per stem. Heavy pruning is best carried out in late autumn early winter when all leaves have been abscinded.
Wiring: Styling is best carried out with the ‘clip and grow’ method. If wiring is required, apply in autumn and protect with raffia to ensure branches do not scar, remove before the end of spring.