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Plant a Border - pot sizes.

Updated: May 4, 2023

Plant pots. Something that we all need to think about when we're buying our plants. The environmental impact of plastic pots is something that needs careful consideration but that, for now, is for another day. Let's have a look at plant pot sizes.


plant pot sizes a useful guide

The pot on the left is what's known within the industry as a 9cm pot. The one on the right is a 3 litre pot. One is clearly bigger than the other. The one on the right is 4 times the size of the one on the left! Now why's that an important consideration when buying plants? Well the size of the pot is critical to your plant's development and it's chances of survival. When you buy your plants online it's important to buy plants that have been grown in the size of a pot that provides not just the cheapest plant but that also represents the best value. Some suppliers avoid making the size of the pot that clear. Those plants might look inexpensive when compared to others - those grown in the 3 litre pots for example - but in the long run they can often mean much slower plant development. Plants that are supplied in a 9cm pot are often less than a year old. What that means is that some varieties can be more difficult to plant straight into your garden and to get established.

Plants in a 3 litre pot are usually older and have had extra time to develop. They'll have been potted on as they've grown and developed a strong and healthy root system.

Here's those pots again. Let's think about how much of a difference there is between a 9 cm pot and a 3 litre pot. Well having racked my brain to remember how to work out the capacity of the shape of that 9 cm pot - it's neither a cube nor a conical frustum (!) - I gave it the benefit of the doubt and assumed it was a cube.

And a 9 cm cube has a volume of 0.7 litres. So a smaller pot by far when compared to it's 3 litre cousin. 4 times smaller........ That means that a plant in a 3 litre pot has 4 times the amount of growing medium and space to develop a strong root system. And that has to be a good thing for eventual plant development and growth. So that plant in a 9cm pot might not be the bargain that you first thought - particularly if it fails or if you're hoping to make more of an impact with your planting scheme. In addition the images of the plant that you think you are buying are often stock images, and don't represent the true size of the plant that you'll actually receive. And there's one final thing you need to think about. Not just the size of the pot and whether you want to buy your plants in 9 cm pots or 3 litre pots. It's also the price that you end up paying for them. I had a quick "price check" when I started researching and writing this. One of the 2021 and 2022 favourites for the herbaceous and wildlife borders has been Salvia Royal Bumble. Ignoring all those who offer 9 cm pots, or 3 x 9 cm pots, or 2 litre pots the best I found was one in a 3 litre pot for £22.99. But they're sold out anyway! I then read the price again and asked myself the question how much?! I'm selling mine, delivered to your door for free if you're within a 25 mile of Frome and subject to a minimum order for a lot less.


Make sure when you're looking at plants - either online or in garden centres - you're comparing equivalent pot sizes. Not apples with pears.


And if you do happen to be looking online it might also be worth asking yourself whether that image of the plant is an image that is of the actual plant that you're about to buy.


That way you'll not be in for a surprise when your plants get delivered!

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