You are standing in a nursery aisle, looking at a plant with a woody stem, a rounded crown, and a tag that says "large shrub." Next to it sits a plant of nearly the same size labeled "small tree." Two plants, two words. So which is it? Once you know what botanists and gardeners actually check, the labels make sense.

Plenty of people are asking. In Google Trends data for the US over the past 7 days, top related searches for the seed term "shrubs" included "trees and shrubs" with a score of 100, "shrubs plants" (96), "what is shrubs" (85), "what are shrubs" (64), "tree shrubs" (60), "shrub" (58), "bushes" (54), "flowering shrubs" (49), and "shrubs and bushes" (25). Top scores are relative interest, scaled so the top related search for a seed equals 100; they are not search counts. These were top related searches, not rising ones, so there is no growth percentage to report.

Trees and shrubs: what the words actually mean

The honest starting point is that there is no single official line. Both trees and shrubs are woody plants. The difference is in how the stems are arranged and, by convention, how tall they get.

The Royal Horticultural Society (RHS), in its plant-type pages, describes trees as having a permanent woody structure, usually a single trunk and a network of branches. On its shrubs page, the RHS says shrubs tend to produce multiple woody stems that sprout from low down. It also admits that it can sometimes be hard to distinguish between a large shrub and a small tree.

Single trunk versus multiple stems

Structure is the first test. A tree, in the usual sense, sends up one main stem and holds its leafy branches high above the ground. A shrub sends up several stems from near the soil line, so the plant looks like a clump rather than a column.

The wording varies slightly from source to source, but the idea is the same. The St. John's Abbey Arboretum says shrubs have several main stems sprouting at ground level instead of one trunk, and that they are usually, though not always, shorter than trees. A 2016 paper in Frontiers in Plant Science by Frank Götmark and colleagues defines a tree as a tall perennial plant with a single free-standing woody stem, and a shrub as a short perennial plant with multiple free-standing woody stems branching at or near the ground. So even the plain version comes with "usually" attached.

The "walk under it" test

Popular Science, in its article on the difference between a tree, a shrub, and a bush, quotes the ornithologist David Allen Sibley with a rule of thumb: if you can walk under it, it is a tree; if you have to walk around it, it is a shrub. The same article quotes him concluding that developing a precise definition of a tree is difficult and unrewarding.

How tall is a shrub? The height conventions

Height is where the numbers show up, and where the sources disagree. Here are three conventions, each from a named source.

Notice the gap. A plant 15 feet tall would be a tree by the Cornell convention and a shrub by the National Park Service one. Neither is wrong; they draw the line in different places.

The University of Florida IFAS Extension post explains why a fixed cutoff is shaky: sunlight, water, soil conditions, soil pH, nutrient availability, and genetics all affect mature height. The post calls the Cornell definition "not a perfect definition, but it is a starting point." We agree with that framing.

Bushes, flowering shrubs, and other words people use

"Bush" is the everyday word, and it is looser than "shrub." Popular Science quotes Deanna Curtis, a curator at the New York Botanical Garden, who looks at visible structure: if a plant is so dense that you cannot even tell whether there is a trunk, odds are it is a bush. In casual speech, "shrubs and bushes" are used almost interchangeably, and that is fine.

"Flowering shrubs" is a different kind of phrase. It adds a trait, flowering, that has nothing to do with form. A flowering plant can be a tree, a shrub, or neither. So when you search for flowering shrubs, the word "shrub" is doing the structural work, and "flowering" is only telling you what the plant does in season.

The phrase "tree shrubs" points straight at the overlap this article is about. For another place where the word "tree" gets stretched, see our guide to whether palm trees are trees.

Why the line is fuzzy

Several things blur the boundary between trees and shrubs. A few are worth naming.

• Multi-stemmed trees. Götmark and colleagues write that trees can have multiple stems, and they propose that such trees may be told apart from shrubs by stem form as well as height.
• Intermediate forms. The same paper says it is sometimes difficult to identify a woody plant as a tree or a shrub, and that intermediate forms exist.
• Continuum, not categories. Popular Science presents woody plants as lying along a spectrum, with exceptions in both directions: shrubs that can grow into trees, and trees that can be pruned or bred to look like shrubs.

The words are tools for communication, not rulings from nature.

One plant, two labels: Vitex agnus-castus

A good example of the fuzzy line is Vitex agnus-castus, the plant behind the common name chaste tree. The name says "tree," yet horticultural guides tend to say more than that. The North Carolina State Extension Plant Toolbox describes it as a deciduous tree or shrub with an erect, open, rounded habit, and its plant type lists both Shrub and Tree.

The same page says the plant is usually grown as a shrub, about 10 to 15 feet tall. It adds that in warmer climates it can be trained to grow as a small, single-trunk tree or a large shrub, and that in tree form it can reach heights and widths of up to 20 feet. Its attribute listing gives a height range of 8 to 20 feet.

Read that against the conventions above. At 10 to 15 feet with several stems, it passes the multiple-stem test for a shrub and stays under the National Park Service 20-foot tree line. At 20 feet with a single trunk, it sits at the edge of the Cornell tree line. Same species, same name, and the label depends on the form and the source. If you want to read more about the name itself, see our post on what chaste tree berry is.

Our take on shrub, tree, and bush

We think the most useful definition is the simple one. Look at the base of the plant. One trunk rising from the ground means tree. Many stems rising from near the ground means shrub. Height is a convention layered on top of that, and it changes depending on who wrote the guide.

We also think it is fine to let the labels flex. The plant does not change species when its form changes.

And "bush" deserves more respect than it gets. It is not a technical term, but it is an honest one. Use "shrub" when you want to be precise about stems.

Why we carry it at PRSPR

We wrote this botany guide as part of our Learn library, and it sits alongside our Chaste Tree. This article is about how trees, shrubs, and bushes are told apart and where the line gets fuzzy, nothing more, and so it is not about the product. Here is what the listing states:

• Name: Chaste Tree.
• What it is: a dietary supplement made with Vitex agnus-castus (chaste tree berry).
• Price: $37.99.

It is made in a GMP-certified facility and third-party batch tested. You can see it with the rest of our line in the Vitamins & Supplements collection.

See Chaste Tree at PRSPR

FAQ

What is a shrub?

The Royal Horticultural Society says shrubs tend to produce multiple woody stems that sprout from low down. Cornell University, as quoted by University of Florida IFAS Extension, describes shrubs as woody, perennial plants with a number of stems usually produced from near the soil line.

What are shrubs compared with trees?

Trees usually have a single trunk and shrubs have several stems, according to the RHS. Height conventions differ: Cornell uses about 12 feet, and the National Park Service, as reported by Popular Science, uses 20 feet.

Is a bush the same as a shrub?

In everyday speech, mostly yes. Popular Science quotes Deanna Curtis of the New York Botanical Garden saying that if a plant is so dense you cannot tell whether there is a trunk, odds are it is a bush. "Shrub" is the more precise word.

Can a plant be both a tree and a shrub?

Sometimes the label depends on form. The North Carolina State Extension Plant Toolbox lists Vitex agnus-castus as both Shrub and Tree, and says it can be trained as a small, single-trunk tree or a large shrub. The RHS notes it can be hard to distinguish between a large shrub and a small tree.

How tall can a shrub get?

Cornell says shrubs are generally less than 12 feet, with some exceptions reaching 20 feet or more. Götmark and colleagues note that shrub heights range from about 0.2 meters to about 10 meters.