Most commonly, growers use caliper, container size, and height (inches or feet) for units of measurement for nursery stock. Why do we need multiple units? Because all plants are uniquely different and grow differently. In any of those 3 size units, it’s safe to equate a smaller number with age, weight, and price. We aim to stock a range of sizes for any one species; however, not all sizes are always available.
The simplest way to understand the sizes of nursery stock is to understand where the plant was grown. Plants listed in container sizes are raised in plastic containers. Plants listed in caliper or height sizes are raised in the ground on the farm - they sit for many years (before you're aware they exist) to become a larger - instant gratification - size. And, again, it’s safe to equate a larger size with maturity, weight, and price.
To help make sense of all the options, let’s start small and work our way up.
Container Grown Trees are very popular these days, but not all container sizes are equal. Containers are light-weight, easy to transport in bulk, and allows us to offer certain trees outside of standard harvest dates. A lower container number (i.e #5 Container) generally means a younger, lighter weight, and lower price plant. And vice versa, a larger container number (i.e #25 Container) generally means the plant is more mature, heavier weight, and higher price.
A quick note about containers. The term “gallon” is a moniker carried over from the past when growers used to grow plants in milk jugs. Although still commonly used to describe the size – it’s not technically accurate. Nursery containers are not volumetrically accurate to milk gallons. In addition, container manufacturers often have different sizes for the same container, meaning the size of an empty #10 container may vary slightly among manufacturers.
You will find perennials in sizes as small as Pint and as large as #5 containers. A #1 container is the most common size for perennials. Perennials are only available in container sizes.
You will find trees, shrubs, and evergreens in sizes as small as #5 containers and as large as #25. Once you surpass a #25 Container size, shrubs and evergreens measure by height (in inches or feet), and trees measure in caliper.
Caliper is the measurement of the diameter of a tree trunk, in inches. These trees are planted as babies in farm fields and grown to more mature sizes. When they’re harvested, the root zone is wrapped in burlap, set in a wire cage to protect the root mass, and safely held together with twine – called balled & burlapped (B&B) plant stock. Johnson’s Nursery measures caliper at 6” above the root flare. In our inventories, you’ll see 1.5” caliper (the smallest size we’re willing to sell a field-grown tree) and up. A homeowner is likely able to transport a smaller tree from 1.5” to 2.5” caliper without professional help. We recommend delivery beyond that size.
If you want instant gratification, then you will likely encounter this additional note about about field-grown plants. They've been sitting in the ground for years, so they are acclimated to their environment on the farm. All plants react differently to harvesting - having their roots cut. Harvest windows and dig times directly impacts the availability of mature trees, shrubs, and evergreens. Plants are living things and they all react differently to harvesting at certain times of the year. For example, Birch and Oak trees only tolerate a spring harvest. We harvest as many as possible, then that's it until next year. Maples on the other hand are a popular tree that will harvest well in spring and fall. Customers keenly aware of this pre-order spring-only harvest plants in fall/winter. The "best" looking plants are tagged in the order in which we receive them - first come, first serve.Why are larger plants more expensive? We encourage you to read about Tree Cycles to better understand how long plants take to grow from seed to salable.
There are even larger caliper trees in our inventory, such as 6.5” Caliper and even 8” Caliper (and beyond); however, they come with a price. For years, these larger trees occupy valuable space and resources and receive professional care. Larger trees have much larger root masses and are significantly heavier. They require larger machinery and more labor to harvest and transplant. To put this into perspective, the weight of a 1.5” caliper tree can be 250lbs; the weight of a 6.5” caliper tree can be between 2500-4500lbs – depending on the type of tree. Johnson’s Nursery often manages specimen tree and evergreen projects where a single tree occupies an entire semi.
Shrubs and evergreens that are larger than a #25 container measure by height - inches or feet. These plants are field-grown, balled & burlapped stock. The concept is the same as our discussion about trees and caliper size above. Since they're not the same form as typical trees (a trunk and canopy up top), field-grown evergreens and shrubs are measured by their height.
People like options. The largest percentage of tree inventory grows in single stem form. Roots lead to one trunk, which leads to a canopy up top. You can expand this topic by understanding nursery stock shapes, which discusses how some trees grow as single stem, multi-stem, or shrub form options. Multi-stem and shrub form trees are measured by height.