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The Proper Pot Size for Plants in Container Gardening

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Looks aren’t everything when it comes to choosing containers for plants. The size of the containers plays a major role in how well your plants grow. The amount of soil in the pots and the pots’ height and width determine how well the containers fit your planting needs. Choosing the correct pot size is key to a thriving container garden.

Size Significance

The plants you grow in your container garden need enough space to grow well. Their roots need space to grow within the pots without becoming root bound. A large container allows soil to retain moisture better than a small container; so the container’s plant won’t dry out quickly. Bigger isn’t always better, though. If you plant a small specimen with a shallow root system, then an oversized container can make it difficult to keep the right moisture balance in the soil.

Height vs. Width

The size of a flowerpot involves a few dimensions. Height is often an obvious measurement of a container. Plants with deep roots need tall pots so the roots have plenty of room to grow downward. Plants such as many succulents that have shallow root systems don’t need deep containers. The width of a container is also a consideration. For example, a tall, narrow pot won’t work well for a large plant. A wide, short pot, however, would work well for an arrangement of several succulents.

Plant Size

Deciding what you’ll plant in your container garden is essential before choosing the garden’s pots. Match the containers to the plants, but don’t look at the plants’ initial sizes. Instead, use the plants’ mature sizes as a guide for choosing pots so the plants have room to grow. A tomato plant (Solanum lycopersicum) that is a seedling might fit into a 6-inch-tall pot, but soon it will outgrow the space and need a much larger container. As a general guide, choose a pot with room for at least 1 or 2 gallons of soil for herb plants and annual plants that bloom. Perennial flowering plants, vegetables and large plants need pots that can hold at least 5 gallons of soil. A large pot also is necessary when more than one plant will be in the container. Give each plant enough space to grow fully.

Upgraded Pots

If you already have an established container garden, then re-potting some of its plants in larger containers as the roots outgrow their spaces may be needed. Perennial flowering plants in particular often need to be transplanted into larger containers. If water seems to run through a container without soaking into the soil, then the container’s plant may be root bound and in need of a transplant to a bigger pot. Choose a container that is a few inches larger than the old pot.

Based in the Midwest, Shelley Frost has been writing parenting and education articles since 2007. Her experience comes from teaching, tutoring and managing educational after school programs. Frost worked in insurance and software testing before becoming a writer. She holds a Bachelor of Arts in elementary education with a reading endorsement.

The Proper Pot Size for Plants in Container Gardening. Looks aren’t everything when it comes to choosing containers for plants. The size of the containers plays a major role in how well your plants grow. The amount of soil in the pots and the pots’ height and width determine how well the containers fit your …

Plant Pot Sizes: The Complete Guide

Why are there so many different pot sizes on the market?

Nurseries sell plants at different stages of growth. Most are grown in the ground and then transferred into a pot. Thus a 1 year old tree may be transferred into a 9L pot, a 3 year old tree into a 18L pot. Others are transferred from pot to pot, from a 3L to a 9L for example.

Thus a tree may start out in the ground, before being transferred to a 9L and then a 15L, and so on. A nursery may start out with 300 trees and sell 150 bare root, 100 9Ls and 50 15Ls. Although, not all nurseries do this. Thus a tree may remain in a pot it was initially transferred to.

Different nurseries sell their plants at different stages of growth and use different size pots. This increases the number of pot sizes on the market.

Is pot size a good measure of value for money?

No. You don’t want a larger pot of soil, but a healthy tree with a well established root system and lots of growth. Thus, you should look at the height on arrival and the age of a tree. For larger tree sizes, looking at a tree trunk’s girth is a good measurement of value.

One particular pot size may seem very competitive in comparison to another, but this does not mean you are getting better value. Some nurseries set up complicated irrigation and fertiliser systems ensuring trees receive the best possible nutrients, while others do not go to such lengths.

Similarly, the age of a tree is not the be all and end all. A well fed tree will grow faster than a poorly fed tree. This is why you look at the height on arrival also.

Are smaller or larger pots better value for money?

The younger the tree you purchase the easier it will establish and easier it will be to train. The older the tree you purchase the greater the instant impact it will make and the less you will have to wait for fruit.

Why are 9cm pots not marketed in litres?

Interestingly, 9cm refers to the pots diameter, as opposed to height. All pots smaller than 1L are listed this way, probably because receiving a 0.43L pot sounds a bit rubbish.

Are all trees supplied in pots?

Trees can be sent from late autumn to early spring when they are dormant without any soil – these trees are known as bare root. Potted trees can be transferred anytime in the year, although are best purchased and planted in the colder months as to avoid water stress.

9cm Pot

The smallest pot size available. Plants supplied are usually herbs and shrubs. Many hedging plants are sold this way, allowing you to grow a hedge on the cheap.

2-3L Pot

Climbing plants, both fruiting and ornamental, as well as shrubs are sold at this size.

Roses are sold at this size as their roots grow deeper than other shrubs.

The smallest pot size, you’ll likely be able to buy a tree at.

9-12L Pot

The standard size for 1-3 year old trees. Trees are transferred into this larger pot size, either from the ground or 3L pots.

As young trees are transferred to these larger pots after the bare root season ends in spring, buying in Autumn is recommended, when the tree has adapted to the pot and had more time to grow. A downside of this is that some varieties may have sold out by this point, so for lauded trees buy early!

This is the first size standards are available at. Standards have a portion of the trunk cleared of stems for ornamental value.

Trees above this size are marketed as producing an instant impact.

15-100L

Trees are available in a large number of pot sizes in this range – 15, 18, 25, 30, 45, 50 and so on – with larger pots containing older, more mature trees. The greater the maturity, the greater the instant impact.

Fully grown trees are supplied at this point and at great cost, due to the cost of delivery and years in the nursery.

Approximating Plant Pot Sizes

Litres are difficult to approximate without prior knowledge. Below, you can see our infographic of the relative size of different litre plant pots.

Calculating Plant Pot Sizes

Comparing plant pot sizes is difficult as they vary in shape by manufacturer. At small sizes plant pots are flat-topped cones, while larger sizes are more structurally stable cylinders. This is why we recommend you calculate a pot’s litreage yourself.

Most plant pot sizes are measured in litres, which is a measure of volume, calculated from a shape’s cubic centimetres. A cylinder’s cubic centimetres is calculated from the equation πr 2 h. Thus to calculate you plant pots literage, you need to measure your pot’s height and radius with a ruler. If your plant pot isn’t an exact cylinder, but a flat-topped cone, it is best to approximate calculating a cylinder.

If your pot is a square or rectangle, calculating the cubic centimetres is easier. Simply, multiply the height by the width by the diameter.

Now you have calculated the cubic centimetres of you pot, simply divide by a thousand to arrive at litres.

Too complicated? Below you can see the measurements of various cylindrical pots that were visualised in the above infographic. In our calculations we have presumed the radius is two/thirds of the height.

In the table, you can see that a 3L pot is 44% larger than a 1L pot. Luckily, a cylindrical 3L pot will always be 44% larger than a 1L pot, regardless of the ratio of radius to height.

From the table, you can calculate how much larger a 25L pot is to a 1L pot by calculating percentage change. Simply minus the old height from the new height, then divide by the original height and then multiply by hundred. ((26.16-9)/9) x 100. Thus the percentage change is 190.67%.

We know this is correct as if we multiply 9 by 2.9067 (converting the percentage to a decimal) we arrive at 26.16.

Jorge works in the Primrose marketing team. He is an avid reader, although struggles to stick to one topic!

His ideal afternoon would involve a long walk, before settling down for scones.

Jorge is a journeyman gardener with experience in growing crops.

Why are there so many different pot sizes on the market? Is pot size a good measure of value for money? And learn how to calculate the perfect pot size!