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.
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.
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.
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.
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!
Plant Pot Size Guide
Pot sizes are listed in litres capacity. They are usually black plastic, although an increasing number are being grown in taupe coloured pots to enable waste pots to be collected at the roadside.
Please do not hesitate to contact us if you have any questions on 01423 330234.
Please note the above guide is for illustration purposes only and are not sized proportionally to one another.
9cm – We generally use our P9 pots to grow our stock on from, our most common p9 lines are Ilex aquifolium and some herb and herbaceous lines. Our p9 pots are generally square.
2L – Our 2L pots are ideal for the production of amenity plants grown for one year, most commonly used for our 2L herbaceous and shrub lines, this size is great as the plants are small enough to establish but large enough to make an impact when first planted.
3L – Slightly larger than a 2L, we generally use these for our garden centre plants and some amenity lines.
5L – A 5L is Ideal for the production of bigger shrubs with a larger root capacity, these can be seen across our nursery but generally found within our garden centre sales.
10L – This is our most common pot for ‘specimen plants’ that have generally been grown for two years +.
20L – Used for specimen shrubs such as Rhododendron and conifers and some small trees.
Needing pot dimensions? here's our guide to