Smaller understory trees for a tight spot

I recently received the following question about how to choose a smaller understory tree.

I have a small backyard, and I’d like to add a two or three small deciduous trees or shrubs that will form distinct trunks…There are some good native understory trees, like redbuds, witch hazels, hornbeam, etc. These all come in standard varieties and dwarf varieties.

The redbuds, for example, have dwarf varieties like Rising Sun and Hearts of Gold, which supposedly reach a height of 10 to 12 feet. The standard variety gets at least twice that big. I’d like a plant in that spot that stays 10 feet or less…

Is it better to choose a dwarf variety or to plant the standard variety and prune it?

 

Great question.  There can be many different goals to pruning. However for the majority of the pruning I do, one goals as I have written about before is keeping your plants smaller.

Minimize Pruning Needs

Most people do not have the time or skill required to make their tree look it’s best, especially when trying to limit it’s size. Even if you can, you might not want to have to do it.

I am all for trees that look great and stay small enough to fit their spot without a lot of pruning.

In fact in my own yard, I have resisted doing size control on my ornamental trees. I prefer to buy trees that will mature to an appropriate height for their spot. I have talked about some of my favorites in past posts, including:

• Fox Valley River Birch which grows about 12 feet in 15 years instead of a Heritage River Birch which can get 40-70 feet tall.
• Vanderwolf Limber Pine which grows 40-50′ tall and only 20′ wide instead of a white pine which could grow to 60-80′ tall and 40′ wide.
• Threeflower maple and Paperbark maple, two outstanding trees which won’t get much taller than about 25 feet.

Heck, I have even written an entire post about why we should consider planting smaller shade trees for our landscapes.

Most trees Can Be Kept Much Smaller

That said, most trees can be kept quite a bit smaller than their normal height with consistent pruning. The under story trees I listed below can be kept to around two thirds of their normal height with an annual pruning regimen. I also included one shrub that can also provide some distinct trunks with pruning.

Dwarfs will do it on their own

A dwarf cultivar of these trees could meet your size requirement needs and require less (or no) pruning. If you want to find a dwarf version I  would look it up in Dirr’s Manual of Woody Landscape Plants* which you might be able to find at a local library. You could also just Google “dwarf” + the plants name.

How to Choose

Which to choose is probably more of a question of what you can find.  Depending upon what you find, you will have one of three choices:

1. If the dwarf version of the tree you want is available in a size large enough you would be happy with today. Buy it. 
2. If not, get a smaller sized dwarf version of the tree and curse me for suggesting you buy a dwarf because it is taking forever to grow!
3. Buy the regular version of the plant and commit to learning how to prune it annually.

Some Good Understory Trees

Paw Paw (Asimina triloba)

• Shade tolerance of light to full
• Size: 15 to 20′ high and wide
• Growth rate: Medium

I started with this tree with big tropical like leaves because if you like how it looks, it meets the needs of a small understory tree with distinct trunks. It can be difficult to transplant and should be planted as a small tree (3-6′) to have better luck with it. It is a great native tree for gold to yellow fall color.

It will be more open growing in deep shade. If you only plant one, you will not get fruit as you need two different cultivars for fruit to be produced. I have never pruned these. But their form looks fairly simple to prune back with simple heading cuts on 1st year wood.

American hornbeam, Ironwood (Carpinus caroliniana)

• Shade tolerance of light to full
• Size: 20 to 30′ tall and wide (6 – 9 meters)
• Growth rate: Slow. Averages 8-10 feet in 10 years.

Does best in moist soils, but tolerates drier sites. Can be difficult to transplant and is best planted small. Moderately slow grower. It has a good yellow to orangish fall color. Seems to tolerate pruning fine, but does not look it’s best with heavy pruning. Light and frequent pruning is better then one heavy pruning session every few years.

Common witchhazel (Hamamelis virginiana)

• Shade tolerance of light  to full
• Size: 20 to 25′ tall, 15 to 20 feet wide
• Growth rate: Medium

Yellow, fragrant, strap like flowers in fall. They are often at the same time the leaves have colored yellow and are still on the tree. Does best in shade and moist soils. I personally struggle with getting these trees to look natural. They can be pruned heavy but their alternate branching with severe angles make them a challenge (at least for me!)

Redbud (Cercis canadensis)

• Shade tolerance of light to medium
• Size: 20 to 30′ tall and 25 to 35′ wide
• Growth rate: Medium (1 to 2′ per year)

Rosy pink purple flowers open on bare branches in early spring. Pale yellow fall color. Enjoys moist well drained soil. Does not tolerate water stress well especially drought. Can bounce back from a severe pruning and grow four feet in a year. You have to anticipate that and prune it quite a bit smaller than you want it to be the next year.

Pagoda dogwood (Cornus alternifolia)

• Shade tolerance of light to medium
• Size: 15 to 25′ tall and wide
• Growth rate: Slow(<1′ per year) until well established, then medium (1-2′ per year)

Interesting horizontal layered branching. White flowers in late spring not as showy as flowering dogwood, but still attractive. Fruit turns from red to  dark blue in late summer. Does best with cool shaded moist sites.

Light pruning is best as these trees have an architectural effect with their layered branches already. May not be the best candidate for heavy size control pruning. It is better to use light pruning to enhance the plants natural branching patterns through thinning out small branches, etc.

Serviceberry, Juneberry (A. x grandiflora)

• Shade tolerance of light to medium
• Size: 15 to 25′ tall, 10 to 20′ wide
• Growth rate: Medium

White flowers appear in early spring and are followed by very tasty edible blue berries in early summer (June). You will have to beat the birds to them if you want to indulge. Does best in moist soils, but tolerates dry sites. Yellow to red fall color can be excellent.

Service berry are best kept smaller through annual less severe pruning. Try to avoid making large pruning cuts if possible on service berry as it can effect its health as well as ruin the natural aesthetics of the tree in my opinion.

Highbush cranberry (Viburnum trilobum )

• Shade tolerance of light to medium
• Size: 8 to 12′ tall and wide
• Growth rate: Medium

White clusters of flowers in spring, followed by bright red fruits in the fall that often last well into winter. Fall foliage color ranges from yellow (more in shade) to red (more in full sun). This is a shrub that can tolerate heavy pruning and develop a nice branching structure.

These are my favorite shrubs to prune, as they can be developed over a few years into a near sculptural form. That is unless it is attacked by viburnum borer and half of the plant dies. If you are near a natural area this is more likely to happen. You can control borer with insecticides.