Potting-up tomatoes: why, what, how & when

Do you Have to Pot Up?

Why do you pot up? What is potting up? How do you pot up? When do you pot up? Do you have to pot up?

All great questions. Let’s dive in. To start, look closely at the photo below.

This is an excellent comparison of tomato seedlings that have and have not been potted up. Believe this or not (I’d prefer the former!) all of the tomato seedlings in the photo were planted on the same day. The ones on the left have not been potted up yet. The seeds were sown and haven’t been planted into a larger container yet unlike all of my other tomatoes. They have, unfortunately, stayed in a 6-cell pack container thus far in their growing journey. They will be root bound and stunted. Whereas, the tomatoes on the right were “potted up.” The difference in their health, in their leaf and stem size is visibly evident.

The photo above displays why it is important to pot up.

When you pot up, you are giving the plant more growing space which ensures a larger, healthier and therefore, happier plant. One that will be strong enough to be planted outside when the time comes.

So, what exactly does it mean to “pot up?”

Potting up literally means to plant a seedling into a larger container.

When do you pot up tomatoes?

I start my tomatoes in either a 4 or 6-cell pack. When they grow to be 2-3 inches tall with a couple sets of true leaves, usually about three weeks or so, I pot them up to a larger container ranging in size from 4 to 8 inches (depending on what I have clean and ready!). If I plant into a 4 inch pot, I might even pot up one more time depending on how well they’re growing.

How do you pot up tomatoes?

I fill the larger container with a pre-moistened mix of seed starting soil and regular potting soil. Feel free to add a small handful of compost or worm casting. These seedlings will be in their new container for several weeks longer than where they were first started and will need more nutrients. After your seedlings develop their true leaves, you can also start to give them an occasional feed with diluted fertilizer.

After the soil is added, I tap out any possible air bubbles and make a large and deep hole with my fingers. Drop your seedling into its new space, placing it as deep as possible. Don’t be afraid to go right up to the leaves.

Tomato plants greatly benefit from having their stems buried deep. Roots will form all along the stem when buried under the soil. You should be burying the stems like this both when you pot up as well as when you plant them outside.

Do you have to pot up?

No. Many gardeners bypass this extra step by planting the seed straight into a large enough container where it will stay until it’s ready to be planted outside. Potting up is your preference and can also largely depend on the scale of your growing. Some deem it too time consuming. For me, potting up is one of my favourite parts of starting seeds because it allocates time for me to focus on my plants. It is when I can fully check in with their progress and take my time with them. I’ll take any excuse to get my hands dirty.