#3 Plant Container Size: Dimensions, Volume, and Uses

A #3 on a nursery tag is a trade size, and it’s usually called a 3-gallon pot. The pot is about 11 inches across and 9 5/8 inches deep, but it usually holds a bit less than the name suggests, which matters when you’re comparing prices or planning a container garden. For young trees and shrubs, this mid-range size often turns out to be a smart buy, because smaller plants tend to recover from planting faster than big ones.1OAKTrust. Post-transplant Establishment and Economic Value of Three Tree Species from Five Container Sizes

How Big a #3 Pot Is and How Much It Holds

The # sign marks a size class used across the nursery trade, not a measured gallon. Sizes such as #1, #3, #5 and #7 climb in steps, so a #3 sits between a one-gallon and a five-gallon pot. Older tags and some stores simply say “3 gallon” for the same pot. The label tells you the pot size, not the plant’s age or height.

Some nurseries note that a #3 pot actually holds about 2.5 gallons, not 3.6Nature Hills Nursery. What Do Nursery Container Sizes Mean? The # system is an industry trade size, and pot makers vary slightly in shape and taper. So two #3 pots from different growers may not hold quite the same amount of soil. When you buy potting mix to refill or repot, plan on roughly 2.5 to 3 gallons per pot.

What Grows Well in a #3 Container

#3 pots usually hold more mature nursery plants than small pots, giving a fuller look right after planting while leaving room to grow.7Sheridan Nurseries. #3 Plant Container Size: Dimensions, Volume, and Uses Common shrubs such as viburnum, privet and Indian hawthorn are often moved up from one-gallon pots into this size.8Journal of the American Society for Horticultural Science. Relationship of Plant Growth and Actual Evapotranspiration to Irrigation Frequency Based on Management Allowed Deficits for Container Nursery Stock Young trees such as red maple and baldcypress are commonly sold from #3 pots.9Arboriculture & Urban Forestry (AUF). Effect of Container Size at Time of Planting on Tree Growth Rates for Baldcypress [Taxodium distichum (L.) Rich], Red Maple (Acer rubrum L.), and Longleaf Pine (Pinus palustris Mill.)

Perennials and herbs suit the size too. Clump-forming perennials such as hostas, daylilies and coneflowers are commonly sold in a #3 and fill it with a dense root mass. A #3 often holds a perennial clump large enough to flower in its first season. Woody herbs such as rosemary and lavender do well because they prefer a snug pot with good drainage over a huge volume of wet soil. Mint and similar spreaders are sensible choices here, since the pot confines roots that would otherwise take over a bed.

Root type decides how well the shape suits a plant. Shallow, fibrous-rooted plants like azaleas grow larger tops in wider pots, but extra depth makes no difference.10HortScience. Effects of Container Dimension and Volume on Growth of Three Woody Ornamentals Deep-rooted plants like holly grow better as pots get both wider and deeper.11HortScience. Effects of Container Dimension and Volume on Growth of Three Woody Ornamentals So the wide, shallow-ish #3 shape is a good fit for shallow-rooted shrubs, while deep-rooted ones may outgrow it sooner.

Vegetables work in a limited way. A 3-gallon container can hold about six turnips, two broccoli or kale plants, one or two cabbages, or one Brussels sprout or cauliflower.12LSU AgCenter. You can grow vegetables in containers A single tomato in a 3-gallon pot, though, gave noticeably less fruit than one in a 5-gallon container.13Scholars Archive at Oregon State University. Invest in Vegetables: A Cost and Benefit Analysis of Container Grown Roma Tomatoes (Solanum lycopersicum cv. ‘Roma’) and Italian Basil (Ocimum basilicum cv. ‘Italian’) A #3 works for leafy and root crops, but go bigger for tomatoes if harvest matters.

A plant has outgrown its #3 when roots poke out the drainage holes or form a mat on the surface. Other signs: the pot dries out within a day of watering in summer, the plant tips over easily because the top is far heavier than the pot, or new growth slows even with regular feeding.

At the store, a #1 is cheaper but gives less instant effect in a bed. A #5 looks finished sooner but costs more and is heavier to plant. For most shrubs in a home border, #3 balances cost, weight and visual impact.

The plant tag helps you decide if #3 fits. Look for the mature height and spread, since a #3 is only a starting container, and the eventual size shows whether the plant will go in the ground or need a much larger pot. Dwarf or compact shrub varieties can live in a #3 for a season or two on a patio, while full-size trees are meant to go in the ground soon.

Why #3 Trees and Shrubs Often Settle in Faster

Trees from #3 and #7 containers had less water stress after planting and returned to normal sooner than trees from larger containers.14OAKTrust. Post-transplant Establishment and Economic Value of Three Tree Species from Five Container Sizes Their roots spread out by a larger share after planting, so they grew faster and caught up quicker, giving more value for the money.15OAKTrust. Post-transplant Establishment and Economic Value of Three Tree Species from Five Container Sizes

A plant carries only the roots in its root ball when it’s moved, so recovery depends on how quickly those roots reach into new soil. A small plant has a modest top to feed and a root ball that is a larger share of the whole, so new roots catch up with the demand for water sooner.

In one planting, #3 baldcypress had the best growth and highest survival five years later.16Arboriculture & Urban Forestry (AUF). Effect of Container Size at Time of Planting on Tree Growth Rates for Baldcypress [Taxodium distichum (L.) Rich], Red Maple (Acer rubrum L.), and Longleaf Pine (Pinus palustris Mill.) They were large enough to be noticed and not trampled, but small enough to avoid severe transplant shock.17Arboriculture & Urban Forestry (AUF). Effect of Container Size at Time of Planting on Tree Growth Rates for Baldcypress [Taxodium distichum (L.) Rich], Red Maple (Acer rubrum L.), and Longleaf Pine (Pinus palustris Mill.) With much larger trees, size differences in growth rate tend to disappear.18Arboriculture & Urban Forestry (AUF). Effect of Container Size at Time of Planting on Tree Growth Rates for Baldcypress [Taxodium distichum (L.) Rich], Red Maple (Acer rubrum L.), and Longleaf Pine (Pinus palustris Mill.) Transplant shock shows up as leaves that wilt or scorch even when the soil seems moist, and new growth that is small or stops for a season.

To care for a newly planted #3 tree or shrub, water deeply and regularly through the first growing season, since roots are still confined near the original root ball and the surrounding soil may stay drier than it looks. Keep a few inches of mulch over the planting area, pulled back from the trunk, to conserve moisture without causing rot at the base. Hold off on heavy pruning or fertilizing so the plant can put its energy into new roots first.

Checking and Handling the Roots at Planting

Roots that wrap around the inside of smooth, rigid plastic pots can later circle the trunk and choke the tree.19Arboriculture & Urban Forestry. Nursery Production Alternatives for Reduction or Elimination of Circling Tree Roots Tight or glazed planting holes can cause the same problem in the ground.20Arboriculture & Urban Forestry. Nursery Production Alternatives for Reduction or Elimination of Circling Tree Roots So dig a wide hole with rough sides, not just a pot-sized pocket.

A circling root thickens as the tree grows and can press against the trunk or other roots, restricting water and nutrients. The harm often doesn’t show for years, so a tree can look healthy at planting and decline later.

To unpot a #3, water the pot an hour beforehand so the root ball slides out intact. Tip it on its side and press the pot walls rather than yanking the stem. Then look at the outer roots. White tips pointing outward are good; thick roots wrapping around are a warning. Gently tease circling roots outward with your fingers before setting the plant in.

Slicing the root ball at planting had only a slight effect on drought tolerance afterward.21Arboriculture & Urban Forestry. Effect of Tree Size, Root Pruning, and Production Method on Establishment of Quercus virginiana And shaving the outer roots each time a maple was moved up to a bigger pot reduced how firmly it later anchored in the ground.22Arboriculture & Urban Forestry (AUF). Effect of Container Type and Root Pruning on Growth and Anchorage After Planting Acer rubrum L. into Landscape Soil Gently teasing out circling roots is usually enough; heavy shaving isn’t a must.

Set the top of the root ball level with or slightly above the surrounding soil. Burying the trunk base invites rot. Backfill with the soil you dug out and water deeply to settle it.

Pot Materials and Root Health

Root-pruning containers produce more fine roots and much less circling than standard plastic pots.23Acta Horticulturae. Plant Container Size: Dimensions, Volume, and Uses Fabric pots showed almost no root growth along the sides.24Acta Horticulturae. Plant Container Size: Dimensions, Volume, and Uses If you keep a plant in a container for years, a fabric #3 is a good choice.

Roots that reach the wall of a root-pruning or fabric pot meet air or openings and stop growing in length, so the plant branches behind the tip instead of wrapping around. That means less work correcting roots at planting.

There are trade-offs. Fabric lets air and moisture pass through the sides, so the soil dries faster than in solid plastic and needs more frequent watering. Fabric pots are soft-sided and can bulge or slump, so they need a flat surface and may look less tidy on a patio. Roots can grow into the fabric over time, so lifting a plant that has stayed a long time may take care.

Heat is the other issue. Soil in plastic containers ran about 6 °C (about 11 °F) hotter on average than in wood pulp, fiber or coir pots.25HortTechnology. Substrate Temperature in Plastic and Alternative Nursery Containers In black containers in sun, root temperatures passed 40 °C (104 °F), a level that harms roots and growth.26HortScience. Root Zone Temperatures of Viburnum odoratissimum Grown in the Multipot Box System and Conventional Systems: Measurement and Analyses of Temperature Profiles and Predicting Root Zone Temperatures So shade the sides of black pots on a hot patio or group them closely.

If you’re planting within weeks, the nursery plastic pot is fine. For a year or more on a sunny deck, pick a light-colored or fabric pot. To cool a hot pot, slip it inside a larger decorative pot, place it where afternoon shade hits the sides, or mulch the soil surface to slow drying.

Watering, Feeding and Drainage in a #3 Pot

Watering container plants based on soil moisture instead of a fixed timer cut water use by 21% to 40% with no loss in growth.27Agricultural Water Management. Substrate water status and evapotranspiration irrigation schedulingin heterogenous container nursery crops Plants were watered less often and less water ran out the bottom.28Agricultural Water Management. Substrate water status and evapotranspiration irrigation schedulingin heterogenous container nursery crops So check the soil with a finger an inch down before watering.

A #3 dries out faster than you’d expect. A plant with a large leafy top can use up the stored water in a day on a hot, windy afternoon, and a pot that lasted two days in spring may need daily watering by midsummer.

For a #3 shrub on a patio in summer, water until it drains from the bottom, then stop. In hot weather it may need water daily. A saucer left full can rot roots, and morning watering lets the leaves dry.

A coarse layer at the bottom of a pot usually lowers how much water the pot holds, rarely raises it.29PubMed Central. Effect of drainage layers on water retention of potting media in containers The effect is bigger with coarse, airy potting mixes.30PubMed Central. Effect of drainage layers on water retention of potting media in containers Skip the gravel layer; for soil that stays soggy, use a coarser potting mix and make sure the drainage holes are clear.

More slow-release fertilizer grows bigger plants faster but washes more nutrients out.31HortScience. Controlled-release Fertilizer Application Rates for Container Nursery Crop Production in Southwestern Ontario, Canada The right amount varies by plant; spirea needs less than weigela or hibiscus.32HortScience. Controlled-release Fertilizer Application Rates for Container Nursery Crop Production in Southwestern Ontario, Canada Follow the label’s middle rate unless you want maximum growth.

Pale yellow leaves can suggest too little feeding, though overwatering can cause them too. A white crust on the soil or burnt leaf edges suggests too much, and flushing with plain water helps clear extra salts.

Reusing or Recycling Empty #3 Pots

Most recycling sorters can’t detect black plastic pots, so they end up in landfills.33Association of Professional Landscape Designers. Plant Container Size Dimensions Volume and Uses Sorting machines use light to identify plastic type, and carbon black pigment absorbs that light, so an unidentified pot is treated as waste. Pots are often made of mixed plastics and must be cleaned of soil and residue.34Association of Professional Landscape Designers. Plant Container Size Dimensions Volume and Uses Sunlight makes old pots brittle and unrecyclable.35Association of Professional Landscape Designers. Plant Container Size Dimensions Volume and Uses Reusing pots or returning them to a nursery take-back program is usually the better option.

To reuse a #3, scrub out old soil and rinse with a mild bleach solution to remove disease. It works well for seedlings, divisions or vegetables. Stack spares out of the sun to keep them from cracking.

Many garden centers and nurseries accept clean pots back, since they can reuse them for their own growing. Neighbors, community gardens and school gardens often welcome spares for starting plants and sharing divisions. Recycling programs differ, so check your municipality’s guidance instead of assuming pots are accepted.