How Big Is A Tree In A 15 Gallon Pot?

In the world of Horticulture, the idea of potsize can confuse some gardeners who aren’t so experienced with potted plants. The answer is pretty simple but simply requires some knowledge of pot sizing and what that means for the plant that is within the pot. 

The answer to this question requires some explaining of the tree’s life prior to purchase, how it is grown in a plant nursery and looked after and how that changes as a tree’s life goes on.

Understanding the process of growing the tree commercially within a horticulture setting will shed light on how large to expect a tree to be that is in a 15 gallon pot.

How Do Pot Sizes Work?

Plant pots that are multiple sizes are integral to the horticultural world. Different size pots allow you to accommodate not only different types of plants such as trees all the way down to seedlings, they also accommodate for how mature a plant is.

In simple terms, while many don’t realise this, the size of the pot is about how much soil is in each pot rather than how heavy a plant is. For example, a 5 gallon pot will fit 5 gallons of soil.

But this doesn’t mean that the whole thing (both plant and pot) will weigh 5 gallons, this is simply how much soil a pot can hold. 

Pot sizes are chosen based on the plant you are potting. A perennial flower that is growing in a nursery will start life in a half gallon pot, or less, and could move up to a 1 gallon pot after a few months of growth.

Why Do We Need Different Sized Pots?

This answer is pretty simple – roots. Firstly, different plants have different root structures. While some roots can be short and thin, others can be large and invasive. Moreover, as a plant grows, so does it roots. Different pot sizes accommodate different maturity of plants. 

If your plant has grown over a few months, so will its roots. Eventually, this plant will outgrow its pot. One of the main jobs in a plant nursery is keeping tabs on which plants need to go up a pot size. 

One major reason that people’s potted plants die or their growth is stunted is due to the plant being in the wrong sized pot. If the plant has grown then so has its roots, the plants roots need more room to grow, when kept in a pot that is too small the plant won’t grow anymore. 

This is never more true than for trees. Trees are much slower growing than a perennial or annual flower. In any case, tree roots start much larger than most flowers or smaller plants and are in their own league when it comes to pot size. 

It’s often the case that trees are actively kept in smaller pots when being sold. This is because trees are almost always going to be planted into something bigger, most likely the earth itself.

If trees kept going up in pot size while still at the nursery they would just go up and up in size, when in fact this should be happening in the earth the customer is planting the tree into.

Restricting growth so you can plant a tree in your own earth means that the tree will create a strong root structure, rather than doing this within the pot.

How Big Is A Tree In A 15 Gallon Pot?

This is where things can get confusing but fundamentally makes sense. As we mentioned, a 15 gallon plant pot will hold around 15 gallons of soil. So, before a tree is even introduced to the party, the pot will weigh around 15 gallons.

This doesn’t really dictate the size of the tree at all, the final weight or height of the potted tree falls within a range but is generally going to completely depend on the variety of tree and how mature it is.

For example, a birch tree that fits a 15 gallon pot will be much larger than a Pinus in a 15 gallon pot. 

Either way, we can make some relatively accurate approximations of the size of a tree that is in a 15 gallon pot due to the level of growth that is being stunted.

It’s pretty likely that a tree within a 15 gallon pot will be around 6 – 12 feet in height. This is because, depending on variety, a tree with a soil capacity like this can only really reach a certain height.

As mentioned, this is a purposeful move by nurseries so that when you plant the tree at home it can create a strong root structure. These trees will have been in the nursery for around 1 – 5 years which is why they may be more expensive.

Final Thoughts

So, there you go. Pot size rarely gives an accurate idea of what size the plant may be once grown, rather, it can give a rough estimate of the plant’s maturity which can inform us about size somewhat.

A 15 gallon pot will have 15 gallons of soil in it, this stunts the tree’s growth so that you can plant it at home. This means we can estimate the tree will be around 6 – 12 feet, where it falls in this range will depend on the tree’s variety and how mature it is.

A tree in a 15 gallon pot has likely been growing for up to 5 years so is about halfway to its full maturity.

What we can learn from this is that the amount of soil in a pot dictates how much a plant can grow. If you have plants at home that seem to have outgrown their pot, then its time to go up a pot size and watch your plant grow even further.

Plants are often kept in pots at plant nurseries to stunt growth so that they can grow after they have been purchased and planted. The larger the pot means the larger the price.