How To Gardening How to prune dwarf Alberta spruce

How to prune dwarf Alberta spruce

By Nancy Norris | October 24, 2009

| Last updated on June 29, 2023

Trimming established trees for a more scale appearance

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How to prune dwarf Alberta spruce
In an effort to model conifer trees, garden railroaders usually go to the nearest garden center and find dwarf Alberta spruce shrubs. This classic, Christmas-tree-shaped evergreen has a nice, green color and a densely packed growth habit, giving it a fuzzy look. Picea glauca conica (aka. P.g. var. albertiana ‘Conica’) emerged onto the gardening scene when a pair of horticulturists waiting for a train noticed a “witches broom” growing on a white spruce in Alberta, Canada, 104 years ago. Every dwarf Alberta spruce since then is descended from that dense growth. The mature height in 10 years could reach five feet, or 10 feet in 20 years.

The following pruning discussion primarily deals with P.g. conica. There are smaller varieties, like P.g. ‘Pixie’ and P.g. ‘Jean’s Dilly’, which I rarely prune and use as town and home trees.

I’ve been teaching clients to use the following technique, but I don’t insist on it. Our garden railways are, after all, our personal thumbprints of expression. You might invent a better way, which I’d like to hear about.

The science

forest with station in garden railway
1. Bob Evans bought many dwarf Alberta spruce trees as bare-root cuttings in 1994. He planted a grove and watched as his forest became a hedge over the years. Letting them grow tall allowed stout trunks to form. Finally, he found information on what to do and now keeps trees pruned himself on his Los Arabis Creek Railway. Nancy Norris photo

In a dozen years of visiting countless garden railways, I’ve found that the most-planted tree in just about any state, except in the deep South, is the dwarf Alberta spruce. Like Christmas trees, most are kept in a dense cone, perhaps cleaned of branches near the ground. Years pass. Although a true dwarf shrub, the tree’s DNA creates a cone shape with a ratio of 2:1, height to width. They grow wider and wider, as they gain 2-4″ in height each year. Recognizing this dilemma, some space-conscious railroaders get out the hedge clippers (and, yes, chain saws) to shear the sides and top, occasionally finding brown gaps when finished. This crew-cut treatment will keep the tree small only so long, because the sun-starved inside of the branch eventually runs out of growing points (buds). Dead gaps often appear the next year because the bud-filled tips have been removed, leaving older, non-productive tissue that won’t sprout new growth.

The other issue is that shearing the tips makes the tree shrubbier and denser. The hormones in the tips say, “Oh yeah, cut off my terminal buds and I’ll give you more buds-a lot more” (photo 2). The term for this is “pinching back.” Call it what you like, it works only for a while; then you either have to like the dead look or replace the tree.

The timing

Before you run outdoors with magazine and pruners in hand, let’s talk about when to prune. Dwarf Alberta spruce is recommended for USDA Hardiness Zones 3-8, but I’ve seen healthy specimens in Zones 9 and 10, given afternoon shade and enough water.

In warmer climates, I recommend severely pruning spruce in mid to late autumn so as not to stimulate a new flush of growth, which can be damaged by freezing temperatures. By cutting off bud-bearing branches at this time, you save yourself extra pruning next spring because buds are set on the previous years growth.

Alternatively, prune spruce trees just before or after their spring growth and before intense sun on hot days can burn newly exposed leaves. Some experts say fall pruning also has an advantage because summer pruning can expose new cuts to insect damage.

Those in the colder, northern climates need to prepare their plants for a longer dormancy, so fall pruning may send the wrong message (although I’ve seen recommendations for fall pruning of spruces in Zone 4). After the buds have sprouted and hardened (no longer tender), usually in May or June, a severe pruning in late spring will allow more time to repair for the coming winter. It’s difficult to give advice for every situation in an international magazine so I suggest you test your pruning skills on just a few trees before making a costly mistake. One or two dead trees can model lightning strikes.

The technique

Tree with top pruned off
2. On his Ambitious & Tiring Railroad, a friend, Bob Fergusen, permitted the author to demonstrate pruning techniques on his dwarf Alberta spruce trees, all about 40″ tall by 20″ wide. The top of the tree in the foreground has been hacked off, revealing a dead spot inside. There’s lots of new growth around the apex. Nancy Norris photo

Let’s look at what to do if starting with a dwarf Alberta spruce that has been growing over 5 years in the ground (photo 2). In the photo, notice that a previous attempt to shorten the tree has produced lots of new growth around the dead apex; eventually this would make a bushy flat top. Even though I want to lower the apex, I start pruning at the bottom to see what the tree will tell me.

tree branch with scissors
3. To illustrate the pruning technique, this branch has been removed from the tree. The lower rail in the photo makes a nice, horizontal line to show where the author will prune that branch. Keeping the pruning shears horizontal prevents accidental cutting of other branches. Nancy Norris photo

Spruce branches have what is termed an “opposite arrangement” of branches. Knowing this habit, I prune much of the growth away from the top of each branch, leaving a bottom “branchlet,” and making sure that it has buds. To demonstrate this technique, I have placed a typical branch on a track in the orientation it was on the tree (photo 3). Opposite branchlets on the main branch point up and down, then left and right, and so on.

DNA tells the branch tips to point up, but there is a loophole, called “directional pruning.” We want our lower branches to look heavy and old, and to point outward or perhaps down a bit. In photo 3, the lower rail shows the cutting path I will take with my pruning shears on every branch of the tree, starting by pruning the strongest upward branchlet and leaving the weaker horizontal branchlet on the bottom. I’ll then cut smaller branchlets off that one and finally cut the terminal end to eliminate the strongest, longest tips. I’ll leave the shortest tips, with some buds.Finding the place to start cutting is tricky on a densely branched shrub, as in the branch in photo

3. Pick a branch (any branch) and fold up only the tip to expose branchlets attached to that main branch. If you see a decent branchlet underneath, cut off the big one you are holding up (where it meets the branch). If, when you lift the remaining branchlet, you see another good branchlet underneath, cut off the one you’re holding. Repeat this procedure on the entire tree, except the very top. If you see a cluster of branches coming off the trunk at one point, isolate a weaker one and get rid of the others. Less is more, but don’t model a sparse mountaintop tree in a lush grove.

Decide at what height you want the lowest branches, based on the full-scale tree you are modeling, then similarly decide on the height of the tree. I leave low branches to hide things I find unsightly and remove them to expose goodies. Sometimes the plant will grow one or more secondary trunks and you may need to decide to keep one or part of one to hide a bare trunk on that side.

The apex

Lowering the top is not as difficult as you might think, but harder than just lopping off the top three years of growth, as happened in photo 2. There’s a trick to it.

Using the tree’s “apical dominance,” choose a good-looking side branch a few inches lower than the intended top. Pick a lateral branch on the side of the tree you call the front. Unless you waited about 10 years too long, this branch will be flexible and you can bend it up, snug to the trunk.

tree with branches cut off
4. Sap drips from the terminal cut at the top of the tree but it will soon heal. On its right, the new leader or apex will be tied snug to the stump. Nancy Norris photo

In photo 4, I’ve chosen the branch on the right and cut off the top of the tree to leave an important, but temporary, stump. Photo 5 shows the placement of a temporary (green) twist-tie. Be sure to remove the tie and the stump after the branch has retained the “memory” of its new verticality. Having pruned hundreds of little trees, I occasionally find apices on which I forgot to remove the tie and find that a bulging gall has formed under the tie, while other branches have assumed dominance. This can be fixed using the above technique.

tree branche wired into place
5. Looking at the backside of the apex, we see the green twist-tie holding the lateral branch vertically against the top of the trunk, where the old top was removed. In a few weeks, when the apex remains vertical on its own, the stump will be cut off along with the tie. Nancy Norris photo

Aesthetic pruning

trees with scissors next to them
6. One down. . .now to clean up the branches. The top has been lowered only a few inches, by the author’s choice, but the tree has been reduced many inches on the sides. Note the shelf-like position of the branches. Nancy Norris photo

Finally, in photo 6 we see the results of a half hour of pruning the tree in the center. I decided to begin the bottom branches only 4″ from the ground to hide the street. In the process of pruning, I relieved the tree of two-thirds or more of its growth, not to mention the dead leaves piled up inside with snails, spiders, and a peanut hidden by a jay. Inside branches will be happy to receive the wind, sun, and rain, which will help keep the tree healthy. Spray it with the hose to repel the notorious spider mites during hot spells.

We garden railroaders are actually pioneers in this process of creating scale trees in our gardens. However, we can learn from the bonsai masters and from the tree itself. This method of pruning translates to many conifer species. Because we’re growing plants in the ground, our trees usually have more vigorous root growth than those in pots, helping us achieve greater success.

It may help to have a professional person start the process, which you can then more easily maintain. Such was the case in photo 1, in which a person who had taken a course in “Aesthetic Pruning” got the homeowner past the initial severe pruning so he could then keep them in scale. If you want to experiment, prune a few trees when you feel like it, then see what they do. Get your gloves on!

Learn more about dwarf Alberta spruce.

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