Screening and planting distance
Broadly the Eucalypts offered are either subalpine trees or high altitude forest trees. The subalpine trees are not so fast growing, occur as more isolated individuals but are multi-branching and more wind firm to withstand exposure in their native environment. The high altitude forest trees occur in groups and grow much faster but protect one another from wind. If grown as isolated specimens in an exposed area the leverage exerted by the wind is much greater and can lead to leaf tear, wind scorch or even worse windthrow. So the trees can be divided into two categories of growth habit:
1) Fast growing at 1½-2½ metres a year, tall and tending to shed their lower branches after 3 to 5 years. They will usually be open at the bottom with a single trunk when mature. These species should be selected where an early rapid growing screen is required and where it will not matter that they will eventually be bare at the bottom. Such a situation would be where the screen is some way from the property. e.g. E. dalrympleana, E. glaucescens, E. gunnii and E. urnigera.
2) Less fast growing at 1-1½ metres a year (which is fast compared to most trees), multi-branching with a wider crown and lower leaf cover. They have a smaller mature height. These species should be selected where you require a screen much nearer your property. e.g. E. coccifera, debeuzevillei or kybeanensis. Bear in mind that most of these species will not have leaf cover right down to the ground when mature.
E. archeri, E. parvula and E. subcrenulata fall in between these two categories being moderately fast growing in the early stages but also remaining more branching.
As a screen, where low shelter is not required, plant the faster growing species at 1.8 to 2.5 metres (6ft to 8ft) spacing. Within four years the crowns will have joined. Later it may be necessary to thin them out. Alternatively coppice every other plant on alternate years to keep a thick lower screen.
A popular planting method is to mix slower growing and faster growing alternately at 1 to 1½ metre spacing as a single row. Alternatively plant as a double row staggered 2.5 metres apart and 2.5 metres spacing. The rapid growers providing much earlier screening but then as they open out at the base the slower growers are filling the gaps with their wider crowns. The faster growers are then removed or coppiced.
If you wish to establish a copse or spinney; plant at 3 to 4.6 metres (10ft to 15ft) spacing interplanting with shade tolerant shrubs or small trees. It is probably more interesting to mix faster growing and taller species with slower growing smaller species. For single ornamental specimens use a spacing of at least 4 metres.
The distance that you decide upon will influence their final crown habit. This is because of the competition between trees for the available light. Planted closer together the trees will tend to grow more narrow and have a higher crown than those planted at a wider spacing. Bushy trees will be less bushy at a close spacing. Tall, narrow trees will have a wider crown when planted wide apart.
Occasionally because of their very rapid growth the crown development may appear to be in advance of stem thickening. The tops may lean and be floppy after the first year. If this occurs prune back the leading shoot in March to thicker growth lower down the stem. This is preferable to staking and should cure the instability.