Evergreen Alders will grow up to 8 metres tall and 4 to 5 metres wide, but they love to be trimmed and can be kept at almost any height. If you want a neat hedge shaped screen, trim them 3 times a year, or if you just want to keep the trees small trim them once a year. The time of year for the trimming doesn’t matter – do it whenever you feel like.
If you’re planting a screen you plant them 2-3 metres a part. For an avenue plant them 6 to 7 metres apart.