Mediterranean Spearmint is a vigorous, hardy perennial that will grow happily in a container all year long. Mint plants spread by roots that will eventually fill the container.
In just one growing season, this vigorous grower can become root bound, with roots filling up the container and leaving little soil. The plant becomes stunted, doesn't thrive and produces only small leaves.
Mint will do best if the root ball is divided each year in early spring.
Step-by-step instructions for dividing mint plants
First, lay down a tarp because this is a messy process! Remove the entire plant from the container. You will need a tool to help pry the plant out if the container does not have straight sides like this one. We use a Hori Hori (Japanese Digging Knife) but an old serrated kitchen knife will work as well. You will likely see that the thick roots have started to circle around the sides of the container and they may be quite bound together.
|Remove mint from pot using a Hori Hori|
|Thick roots of mint bound in the pot|
|Cutting root ball in half with a Hori Hori|
|Piece of root ball to be replanted|
|New bag of potting soil to replant into same pot|
|Fill the bottom layer first|
|Replace piece of root ball in center of pot|
|Refill with new potting soil|
|Trim back old stems|
|Newly divided and replanted mint|
|6 weeks later, grown back after dividing|
For pieces you are not keeping but want to compost, you should first shake out the potting soil from the roots and let the roots dry out in the sun for a few weeks so that they will not continue to grow. Mint roots are very resilient! Once they are completely dried out they can be thrown into the compost.