What’s the Difference Between Container Sizes?

We get a lot of questions about what the different container sizes really mean for your landscape. On every product page at Nature Hills Nursery, you'll see a tabbed navigation under the photos with detail about the plants for sale. You'll also find a Plant Sizes tab with a helpful comparison video.

This article goes deeper into the industry history behind how container sizes came to be, what the numbers actually mean, and why Nature Hills approaches container selection differently than many nurseries you'll find at your local garden center.

The short version: container size is about the age of the plant and its root system development, not the liquid volume of the pot. The bigger the container, the more developed the root system, and the faster a plant establishes in your landscape. That's what matters most.

• How Nursery Container Sizes Evolved
• The Trade Gallon vs. the True Gallon
• What the Container Numbers Actually Mean
• NCWM Weights and Measures Compliance
• Why Nature Hills Uses True 1-Gallon Containers
• Selecting the Best Container for Root Production
• How Big Is the Plant in the Pot?
• Life Cycle of a Container-Grown Perennial
• Pot Size Equals Plant Age
• Best Growth in Right-Sized Containers
• Compliance
• Wrap Up: The Root of the Matter

How Nursery Container Sizes Evolved

The nursery industry did not arrive at container size designations through careful planning. It happened the way most industry standards happen: through a quirk of history and market pressure.

After World War II, the U.S. government had a surplus of one-gallon metal cans that had been used for food storage. Nurseries purchased these inexpensive cans in bulk and began growing plants in them, labeling everything as a "1-gallon" plant. That practice set the trade standard for the entire industry and that standard has never fully gone away.

As the industry grew, container manufacturers began offering a wider range of pot shapes and sizes designed to suit different plant types rather than to match liquid volume. A #1 container holds considerably less soil than a true liquid gallon. A #3 container does not hold three gallons of water.

Most nurseries moved to broad size designations (#1, #2, #3, #5, #7) to give buyers a consistent language for comparing plant size and maturity across a wide range of actual pot volumes.

The Trade Gallon vs. the True Gallon

Here is one of the most misunderstood points in the nursery world. When a nursery lists a plant as a "#1 Gallon," most consumers assume that means the pot holds one true gallon of soil (128 fluid ounces, four quarts). It does not.

A trade gallon, the industry-standard #1 container, holds approximately 0.73 to 0.76 gallons of soil volume, about 183 cubic inches. That is closer to three quarts than four. The "1-gallon" name stuck from those post-war surplus food cans, and the size designation never got corrected as the industry evolved.

This matters because it created real inconsistency. A plant sold as a "1-gallon" at one nursery might be in a smaller pot than the same plant sold as a "#1 container" at another, even though both are technically compliant with the loose trade standard.

What the Container Numbers Actually Mean

The full trade container spectrum looks like this:

Notice that the numbers climb faster than the actual volumes. A #3 container holds about 2.5 gallons, not 3. A #5 holds around 3.6. The designations describe the size class, not the measured volume.

This is why the nursery industry and compliant growers like Nature Hills use the word "container" rather than "gallon" when describing plant sizes. See our full size guide for what each container size means in terms of plant age and what to expect when your plant arrives.

NCWM Weights and Measures Compliance

As the inconsistencies in nursery container labeling grew more visible to consumers, regulators stepped in. The National Conference on Weights and Measures (NCWM) Uniform Weights and Measures Law was enacted to bring consistency and transparency to plant sales across the country.

This law requires that every potted plant for sale include:

• Soil volume listed in both U.S. and metric measures
• Contents clearly labeled
• Common or botanical plant names

The standards are published in NIST Handbooks 44, 130, and 133 and are adopted across states, territories, Washington D.C., and the Navajo Nation. They affect everyone in the supply chain: container manufacturers, growers, label producers, and retailers alike.

The American Standard for Nursery Stock (ANSI Z60.2-2025), published by AmericanHort, complements the NCWM requirements by providing uniform language for buyers and sellers: how to measure plants, specify size, and determine appropriate container sizes relative to plant height and caliper. Compliant nurseries use container class designations, not just volume measurements, to meet the standard fully.

This is why Nature Hills uses #1 Container and #3 Container instead of "1-gallon" or "3-gallon" on product listings. The designation accurately describes the size class under these standards, rather than implying a specific liquid volume that the pot does not actually contain.

Why Nature Hills Uses True 1-Gallon Containers

Here is where Nature Hills takes a different path than most nurseries, and it is a deliberate one.

Most #1 container plants in the industry are grown in a trade gallon (the 0.73 to 0.76 gallon pot that dates back to the post-war surplus can standard). It is the industry minimum, and it is widely used because it is the most cost-efficient option for volume growers.

We grow a significant portion of our #1 container plants in a true 1-gallon container, also called a 19cm pot, which holds a full gallon of growing medium. That is a larger pot, more growing medium, and more room for root development than the trade gallon minimum allows.

Why does this matter? Root volume drives establishment speed. A plant with a denser, more developed root system in a larger pot will anchor faster and push new growth sooner after transplanting. The 19cm pot provides meaningfully more rooting space than the trade gallon standard, and that additional space pays off when your plant goes into the ground.

We label these plants as #1 Containers rather than "true 1-gallon" because that is the correct, NCWM-compliant size class designation. Using the trade size label keeps us aligned with industry and regulatory standards. But inside that container, you are getting more than what the minimum trade standard requires.

This costs more to produce. Larger containers mean more growing medium, more space in the greenhouse, and longer grow times. We make that investment because we believe the quality difference is worth it, and because we want the plant you receive to perform well in your landscape, not just look good in the box.

Selecting the Best Container for Root Production

Beyond volume, the physical design of the container affects root quality. This has been an active area of research and innovation in the nursery trade over the past two decades.

Early production containers were simple round plastic pots. As the industry learned more about how roots respond to container walls, new designs emerged: pots with ridges, air slots, and fabric weaves, all aimed at preventing the circling root problem that plagues traditionally grown container plants.

When a root tip reaches a solid plastic wall, it follows the wall and begins to circle. Over time, those circling roots can girdle the plant, restricting water and nutrient flow after transplanting. Newer container designs interrupt that behavior, prompting root tips to branch inward rather than spiral.

In addition to our standard nursery containers, we also grow some of our plants in Root Pouch fabric containers, which use a breathable woven material to encourage air pruning and a denser, more fibrous root ball. You can read more about how Root Pouches work and how to plant them in our Root Pouch planting guide.

Our containers must also be strong, flexible, label-compatible, and built for the rigors of shipping. A plant that arrives in poor condition because the pot failed in transit is a loss for everyone. We select containers that hold up through the full journey from our Ohio growing facilities to your front door.

How Big Is the Plant in the Pot?

Now you know the container story. But what about the actual plant inside it?

Container size and plant height are related but not the same thing. Many factors affect how large a plant looks at any given moment, including:

• Season and time of year
• Pruning method and timing
• Grower location and climate
• Species-specific growth rates

Life Cycle of a Container-Grown Perennial

Perennials are the clearest example of why you cannot judge a plant by its visible size alone. A Bleeding Heart in a #1 container looks completely different depending on when you receive it:

• In March: dormant, with roots in the soil and nothing visible above ground
• In May: 18 inches tall and in full bloom
• In October: dormant again, appearing to be nothing but soil

The container size and soil volume stay the same throughout the year. The root system keeps developing regardless of what you can see above the soil line.

Pot Size Equals Plant Age

The most reliable way to understand container sizes is to think about them in terms of plant age and root system development, not the volume of the pot or the above-ground height of the plant.

When producing new plants, growers match root system maturity to container size. A young liner goes into a small pot. As the root system expands, the plant is shifted into a larger container. The container tells you how long the plant has been in production and how developed its roots are, which is what drives long-term performance in your landscape.

In other words: a larger container means a more established plant, regardless of what the plant looks like above the soil line on the day it ships.

Best Growth in Right-Sized Containers

Getting the container-to-plant match right matters throughout the growing process, not just at the point of sale.

If a small plant is placed in an oversized container, the excess soil retains more moisture than the root system can use, increasing the risk of root rot. If a mature root system is crowded into a pot that is too small, roots circle, soil dries too quickly, and the plant can stress from moisture competition.

At our growing facilities, we match plant age and root mass to the appropriate container size at every stage of production. Plants are shifted into larger containers as the root system develops. This is why the container your plant arrives in reflects real production investment. It is not arbitrary.

Compliance

Nature Hills Nursery ships plants to customers in all 50 states. That means navigating a patchwork of state and local plant shipping regulations, plant health requirements, and consumer protection laws.

• Only legally-sized plants are shipped to regulated states
• Plants are grown under healthy, monitored conditions
• Containers are labeled correctly under the NCWM Weights and Measures standards
• Container designations (#1, #3, etc.) follow ANSI Z60.2 industry standards

When you order from Nature Hills, you are receiving exactly what is described: a plant in the labeled container class, grown to the appropriate maturity for that size, shipped legally to your location.

Wrap Up: The Root of the Matter

Container sizes in the nursery world have a complicated history that blends post-war surplus economics, market competition, regulatory pressure, and ongoing horticultural research. The result is a system that can look confusing from the outside but makes sense once you understand the story behind it.

Here is what matters for your garden:

• Container numbers describe plant size class, not liquid volume. A #3 container does not hold three gallons of water.
• Bigger containers mean more developed root systems. Root development is what drives establishment speed and long-term performance.
• Nature Hills uses #1/#3 container labels for compliance, because that is the accurate, standards-aligned designation, but we grow a meaningful portion of our #1 plants in true 1-gallon (19cm) pots that exceed the trade minimum.
• We invest in better containers because they produce better plants. The cost is real. So is the payoff when your plant establishes faster and performs better over time.

To see how each container size translates to plant age and what to expect from your order, visit our complete plant size guide. If your plant arrived in a fabric Root Pouch rather than a plastic pot, check our Root Pouch planting guide for instructions specific to that container type.

Happy Planting!