What Is Portland’s Planting Zone and What Does That Mean?

If you’ve done any research on what trees do well in Portland, Oregon, you may have come across a planting zone number, either in the information online about a plant or on the tag at the nursery. The official name of this number is the USDA Plant Hardiness Zone, and if you follow the link here, you can find your plant hardiness zone in the United States.

But what is it, and how can you use it? A quick answer is that it’s a system of determining what trees and other plants will survive and thrive in certain areas of North America, using data gathered and maintained by the US Department of Agriculture. By using this historic and current data, you’ll be able to determine whether a certain plant will thrive in your yard.

A quick look at the map indicates that Portland is in Zones 8b and 9a. Zone 8b has average low temperatures of 15 to 20 degrees Fahrenheit. Zone 9a averages lows of 20 to 25 degrees. This means that the minimum temperature in our zone is 15 to 25 degrees. Plants that are hardy enough to survive those temperatures are recommended for planting in Zone 8b or 9a. Deciduous trees are popular in Zone 8, but Oregon supports evergreens well too. Fruit trees can be a little tricky in this zone, but apricots, figs, pears, pecans, and walnuts all can be found in the Portland area.

Here are our five favorite trees to plant if you’re living in Zone 8b or 9a in Portland, Oregon.

1. Monkey-Puzzle Tree

This is a tree that Portland is famous for, and you’ll find them all over the city. The name comes from the fact that it’s “such a monumental maze that, legend has it, someone once said that even a monkey could get lost climbing it.”

It’s an unusual coniferous tree that can grow to be enormous—over 80 feet tall in most cases—and is extremely long-lived. Get this: monkey puzzle trees can live for a thousand years. While the tree is native to Chile, most of these trees planted in Portland date from the 1905 Lewis & Clark Centennial Exposition, where little starts were sold or given away as souvenirs. All these ancient Portland monkey puzzles are simply still children.

This tree’s root system is interesting in that there’s one large taproot and a smaller system of more shallow roots closer to the surface, so be sure you find the perfect spot to plant this, away from sewer lines and other underground work.

2. Autumn Blaze Maple

This is a fast-growing maple variety that will reach a height of 40 to 60 feet and a width of 20 to 30 feet. It’s a shade tree that will grow three to five feet per year under ideal conditions. The best part about it is the gorgeous orange to crimson red colors it will turn in the fall.

The autumn blaze maple is developed from two classic American trees to produce this vibrant color palette: the red maple and the silver maple. With this combination, you get the fast-growing aspects of the silver maple and the strength of the red maple. Not only that, but this tree is adaptable to many growing conditions, though it still prefers well-drained soil conditions, like most maples. This tree is also resistant to insects and disease and tolerant of pollution, which makes it a great tree for both urban and suburban environments.

3. Hemlock

These trees can be fussy when you’re trying to establish them, but once they’re established, they don’t require much care. The most difficult part of planting hemlock is not how to plant it but where to plant it. Hemlocks prefer acidic soils that are moist but not wet and will require frequent watering. They are riverbank trees, like weeping willows. If the area you want to plant a hemlock tree in is elevated or frequently dry, you may want to reconsider and plant another tree that will have a better advantage in that spot.

However, if you have an environment they like, hemlock can be the envy of your neighbors. Hemlocks are known for their graceful, drooping branches. They are conifer trees that can range from 30 to 200 feet tall, depending on which kind you plant. You can identify hemlock from its scaly bark, which can also look deeply furrowed. Another thing to consider: hemlocks handle ice storms better than most trees, but their roots tend to be shallow, so pay attention to whether you get many windstorms in your area before planting hemlock.

4. Sassafras

This tree is a cold-hardy specimen and grows in Zones 4 to 9. It is much easier to grow than hemlock since it enjoys soil that is not only heavy in clay, loam, and sand, but also in acidic soils. It enjoys adequate drainage and grows in part shade and part sun conditions.

More good news: a sassafras tree has a surface root system, which doesn’t cause many problems, such as tangling with underground sewer systems and so forth. It does, however, have a very long and deep taproot. Be sure about where you plant sassafras because transplanting can be extremely difficult.

Once the sassafras has been established, you won’t need to do much pruning other than establishing the shape of the tree. It tends to split into multiple trunks but can be trained into one trunk. And this one also has gorgeous fall colors: expect orange-pink, yellow-red, and scarlet-purple, after a summer of vivid green leaves.

5. Juniper

This evergreen is easy to identify, with its fresh green scent that can’t be matched. Once you establish a juniper’s shape, it doesn’t need a lot of retraining or pruning to keep it. There are more than 170 varieties of juniper, which range from ground cover to shrubs and trees, so be sure you know how tall your juniper will grow before you purchase it. Some of these varieties can have needles or overlapping scales on their branches, and some varieties of shrub can have both types. A juniper will appreciate an area with full sun or light shade and can thrive in any soil condition.

If you have more questions about what trees to plant in our zones in Portland, Oregon, contact your experts at Mr. Tree Service today!