We often tend to plant young trees too closely together. If you are about to plant a forest, look at some mature trees and notice how far they spread out as they grow. If you have already planted trees too closely, transplant a few as they mature. If you feel your young trees seem too far apart, include other types of shrubs or flowers between them. As the trees grow, they'll eventually crowd out the smaller plants. Remember to plant forest trees in irregular patterns rather than in evenly spaced rows. Also, it helps to plant trees in odd, rather than even, numbers.

On a layout it is often preferable to "see the trees through the forest." One way to do that is to have one tree in the grove noticeably taller than the others, sort of a "grandfather" tree. Then mix the size of the other trees to convey the impression of older and younger growth.

Conifers prefer acidic soil and fairly regular water. Drip irrigation systems on a timer work very well because they provide a regular and constant watering schedule.

WHAT VARIETIES TO CHOOSE

One of the most popular small conifers is dwarf Alberta spruce. It grows slowly and well in most areas. Choose varieties adding only an inch or so each year in your climate. You may choose from several colors, ranging through the greens to blue. At full maturity, after thirty to fifty years, such trees usually reach no more than six feet. They make good background forests.

Another reliable, easy grower is Juniper communis compressa. It has a tight, columnar form between three and six inches wide and ultimately reaches a height of five feet. It looks similar to a miniature Monterey cypress and you may plant such trees closely together. They look very good flanking the front door of a house or the edges of a drive.

By contrast, pinus aristata Sherwood compacta needs extra space. It is a dense, bushy miniature bristlecone pine, eventually growing to 14 inches wide and about two feet high. The young trees are symmetrical and narrow-crowned with a mature appearance. Let each individual tree stand out; keep from crowding them. As the tree matures, thin out the finer branches to emphasize the major structure.

Many outdoor railroaders tend to favor pinus mugo valley cushion. It is very symmetrical and picturesque if you prune it to one major trunk but it requires no thinning. It will grow two feet tall and a foot across. Other varieties of pinus mugo grow much faster and some reach six feet in height and 12 feet in width.

In Los Angeles, Outdoor Railroader contributor Peter Dwan created the appearance of a beautiful forest in a very small area using Juniper procumbens nana. The tree normally stays close to the ground but Peter trained one stem of each plant with bonsai wire. As a result the trees stand upright. If you let the branches cascade, the tree will look like a beautiful fir. It grows anywhere, and if one side is bare, face that side to the sun; it will soon fill with new growth. Prune it as necessary, as often as six times per year, to achieve the size and shape you want. And thin the tree heavily once each year to expose the branches.

THE UNDERSTORY

The understory of a forest is the part closest to the soil. The lowest branches of each conifer variety we have mentioned reach right to the ground. The result is a beautiful green background forest. For diversity, you may want to mix understory plantings with the conifers in the foreground of your layout. To do that, prune the lowest branches of the foreground trees up to a third of the height of the trunk. Then plant such shade-loving plants as dwarf azaleas and rhododendrons, fuschia procumbens, dwarf bamboo, certain campanulas, dwarf hosta (miniature lily), dwarf impatiens wallerana, or vinca minor (dwarf periwinkle) beneath those trees. They'll add dramatic color to your forest.

Finally, don't forget you may plant some foreground trees far apart to create an open park land. Between them you may place more colorful plants needing a sunnier exposure.

Next time we'll look at how to use trees on your layout to help define individual scenes.