How to Choose the right tree to plant.

Aug 6, 2019

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A young black gum tree (Nyssa sylvatica) blazing away in autumn.

You might have heard the famous saying: "The best time to plant a tree was twenty years ago. The second best time is now." Well, here you are now, planting a tree. So what is the right tree to plant? It can feel like sort of a big decision, because if all goes well, that tree will probably outlive you. Sometimes it's hard to know how to choose the right tree to plant. There are several important things to consider: your climate or hardiness zone, the growing conditions, the ultimate size of the tree, and your purpose for the tree.

At first it might seem overwhelming when you think about all of the factors detailed below. Don't let this information daunt you; let the process be fun. I think of it as a treasure hunt, or solving a puzzle. It's much more satisfying to look out at a tree that you chose carefully based on good information, than to walk past a tree that you plunked in before realizing that it was going to rain messy fruit all over your parked car. Plus, when someone compliments you on your beautiful tree, you can bend their ear about all of its wonderful characteristics and benefits. Your enthusiasm may in turn spur them to plant a tree. Thus we grow a forest.

How to choose the right tree to plant

Most of us don't have unlimited space around our homes where we want to plant trees. The opportunity to plant one doesn't come around all that often. That's why it's important to choose carefully when you do plant a tree.

There are so many options when it comes to choosing trees, it can be overwhelming. Tree species vary widely in terms of their structure, height, behavior, and growth rate. And your particular site conditions can also affect how a tree will grow, even compared to others of the same species growing just down the street.

Before you take a trip to your nearest tree nursery, or place an online order, here are four steps to think through when deciding on your tree.

Step 1: Know your hardiness zone

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The USDA Hardiness Zone Map is a guide for growing plants, based on the average annual winter minimum temperature. There are 13 zones; the lower the zone number, the colder the conditions get in that area.

The United States Department of Agriculture has developed a Plant Hardiness Zone Map that helps to determine which plants will grow well in any given spot. The map is based on how cold it tends to get in the winter. More than any other factor, extreme cold limits the range of a plant's survivability. That's why you won't find palm trees flourishing in northern Minnesota, unless they are inside a heated greenhouse. Clicking on the link or map above will take you to the USDA website, where you can input your ZIP code to find out your hardiness zone. You can also try the lookup tool below from plantmaps.com. Be aware that the USDA updated its hardiness zone maps in 2012. Different maps and lookup tools may retrieve slightly different results for your area, so try more than one.

It's important to understand that the hardiness zone rating doesn't mean that it will never get colder than the minimum temperature shown for your zone. Nor that you will experience temperatures that low every winter. The latest USDA maps use data collected from 1976-2005, based on the daily minimum temperatures during that 30-year period. When deciding what to plant, note the zone range listed for each species. If you are at one end of the range, your tree might or might not survive if an extremely cold winter hits.

Another key consideration relating to hardiness zones is your micro-climate. The micro-climate refers to the site-specific conditions right where you situate a plant. If your site is protected from the prevailing winds, or bordered by pavement, it might be slightly warmer than the surrounding area. Conversely, if you're on a hill in an open, windy spot, you might experience colder than average conditions. No plant hardiness zone map can precisely predict micro-climate conditions, so look around and think about how other plants in your vicinity have fared, and whether you've noticed warmer or cooler temperatures than what has been predicted for you.

Step 2: What are the growing conditions?

In order to thrive, a tree needs three key things: sunlight, water, and soil nutrients. Each species has a different range of preferences for each leg of this tripod. Some trees can handle dry shade, while others require abundant moisture and full sun. Some do fine in a lean soil, but others require a fertile loam. A lot of trees will survive if the conditions aren't to their liking, but if you want your tree to grow to its full potential, it helps to learn a bit about the growing conditions.

Shade Tolerance

Look at your planting site. Do buildings or other trees cast shade there for much of the day? You might need to take a whole day and check the site in the morning, early afternoon, and late afternoon/evening. A site considered to be in "full sun" receives at least six hours of sun per day. All trees appreciate sunlight, but some are better adapted to growing in lower light conditions than others. Those are known as shade tolerant trees. Species that require full sun are shade intolerant, while those that can take a mix of sun and shade have intermediate shade tolerance. Wikipedia has a nice list of tree species based on shade tolerance to get you started.

Soil Moisture

Think about the soil where you will plant your tree. Is it in a sidewalk median, where there is little exposed soil/vegetation that gathers rainfall? In the middle of your yard? Next to your gutter downspout? On a rise? The answer to those questions will begin to tell you something about how much moisture will reach the soil in your tree's root zone. Also note the texture of the soil at your planting site. Is it heavy and clayey, or loose and sandy? Is it dark brown and rich in organic matter? The more clayey and the higher organic matter content, the greater moisture retention the soil will have. Sandier soils drain quickly, so water quickly seeps down and away from the root zone.

Note that you will need to water your tree for the first two growing seasons after planting, no matter what your soil is like, when it does not get adequate rainfall. It takes a couple of years before the root system grows large enough to be drought tolerant.

Soil Nutrients

Trees have the nearly magical capability of photosynthesis, whereby they spin sunlight, water, and air into sugar (a primary form of energy). But they also need nutrients to grow roots, branches, and leaves. Roots draw up nutrients from the soil and transport them up to where they are needed. If you ever examine a bag of plant fertilizer, you might see three numbers separated by dashes, like 10-10-10, or 30-0-0. The three numbers relate to the three major plant nutrients: Nitrogen (N), Phosphorus (P), and Potassium (K). Additional micronutrients required by trees include calcium (Ca), magnesium (Mg), sulfur (S), boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn).

Some trees are very sensitive to soil nutrient availability, while others are more adaptable. Usually, however, you can adjust the nutrient levels based on a fertilization regime. The ideal scenario is one where you pick a tree species that won't need much fertilization. You want a tree that requires little maintenance given the conditions you offer it.

It can be very helpful to get a soil test to learn more about your site conditions; read my article on interpreting soil test results for more information. Note that you should not fertilize your tree at the time of planting because it can cause a flush of leaves to grow before the root system has a chance to catch up. This can lead to a stressed plant and increased susceptibility to drought, pests, and disease.

Step 3: What is the ultimate size of the tree?

It's easy to pick a tree based on a pretty photo or eloquent description. However, be sure to check on the tree's ultimate height and spread before you plant. Will there be room for the tree once it is full grown? Do you want a 100-foot tree casting a large circle of shade around it, or would a smaller specimen fit the surroundings better? Remember that you might never see the tree at its full size, but future generations will. You don't want them to have to cut the tree down in its prime because it outgrew its site.

Another aspect to consider is the tree's form. There are five basic tree shapes: columnar, vase shaped, round, oval, and pyramidal. A venerable oak has a full, round form. A Lombardy poplar, on the other hand, is decidedly columnar. Elms are classic vase-shaped trees. Try to visualize your tree at maturity and think about how its form will benefit or hinder nearby activities. If you have your heart set on a certain species, it's possible that there are cultivars selected for a certain form, such as compact height, or a more pyramidal shape. See this page about plant terminology for more on deciphering the difference between cultivars, hybrids, and varieties.

Again, try to choose a tree that will reach an appropriate size for its surroundings. You don't want to feel you must prune your tree every year to control its size. That makes for a lot of work, and is also often unsightly and unhealthy for the tree. Allow your tree to grow to its natural size and shape by choosing wisely.

Step 4: Think about your purpose for the tree

Finally, and perhaps most importantly, consider your needs and your purpose for the tree you are planting. Are you looking for a shade tree to cool your home in summer? A beautiful flowering ornamental? A fruiting or nut-bearing tree to attract wildlife? A privacy screen? These questions will help to guide your decision. Maybe you liked the look of a tree you saw elsewhere in your neighborhood. If you can, ask the owner what they like and dislike about the tree. Once you find out what it is, read up on the species to discover its traits. Maybe it has beautiful, fragrant flowers, only to later drop messy cones all over the yard. Or perhaps it is trouble free, with little care required.

If you can, contemplate the wildlife benefit of any tree you choose to plant. Native trees are often the best suited to local conditions, and possess the added benefit of playing host to wildlife. Planting a non-native ornamental tree is fine, but think of it as statuary. Non-native trees are much less likely to host insects that feed on their leaves. Wildlife needs those insects! Birds and mammals depend upon the insects that eat tree leaves for a significant portion of their diet - in fact, native trees form the basis of the food web. By planting a native tree that is well adapted to your site, you will be supporting the natural ecology of your area. Things will literally come alive: birds, bees, butterflies, moths, and all manner of creatures will appear to enrich your environment. Check out this article to learn 10 great reasons to add native plants to your landscape.