Transplanting Tomatoes – When To Transplant Tomato Seedlings

Shortly after your tomato seeds have germinated, they will begin to grow rapidly. Soon, they should outgrow the small seedling cells in which they were planted. This means it is time to up-pot your tomato plants!

Transplanting tomatoes is fairly easy and it comes down to 3 main factors: Timing, delicate handling, and technique. In this article, I will share my method for transplanting tomato seedlings into larger pots. Let’s get started!

Tomato seedlings
Tomato seedlings 17 days after sowing seeds.

What is Transplanting & Why Do It?

First, I’d like to address some common questions about transplanting tomato seedlings. Namely, what it is and why bother doing it as opposed to planting seeds in larger pots to begin with.

What is transplanting?

The process of transplanting tomatoes involves re-potting smaller plants into a larger container. This means moving the entire plant, roots and all, into a larger soil space.

I like to start my tomatoes in small seed cells (around 1″ in diameter), transplant them to 3.5″ pots, and then finally move them outside into their final location. These two moves allow the plants to keep on growing at their natural rate without becoming rootbound.

Transplanting tomato seedlings

Transplanting is fairly easy, but it does require some additional effort, careful handing and proper timing. So why bother transplanting at all?

Why not just plant seeds directly in a large pot?

This is an excellent question that is frequently asked about many types of annual plants, including tomatoes. The answer is threefold: To save space, to prevent overwatering, and to encourage faster growth.

If you were to plant your tomato seeds directly in a 5 gallon container, the seed would sprout, but the initial, tiny plant would have way too much soil. This soil retains more water than a small plant can drink, and so the damp soil may become moldy or otherwise unhealthy. Keeping young plants in smaller pots prevents this and provides just the right amount of water to the small root systems.

Tomato seedlings

Another reason is to save space. Large pots take up more room, and since I plant my tomatoes indoors, having them in smaller pots saves a lot of space in our home. If you only have 1 or 2 plants this may not be a concern, but any more and you’ll want to keep your tomatoes compact until they are outdoors.

And finally, keeping your tomatoes in proportionately-sized pots encourages faster overall plant growth. I’m not sure of the science behind this, but direct sowing in smaller pots has always lead to faster growth for me!


When To Transplant Tomato Seedlings

As your plants grow above the ground, so too does the root system below the soil’s surface. If you leave your tomatoes in a small pot for too long, the roots can become entangled, effectively strangling the plant from below.

This is called a ‘rootbound’ plant, and transplanting at the right time will help prevent it from happening. So, timing is everything! Don’t miss the boat on transplanting tomato seedlings at the right time.

In short, transplant tomato seedlings into larger pots about 2-3 weeks after sprouting. The plants should have 2-3 sets of ‘true’ leaves and the root system should be reaching the bottom of the pots.

Tomato seedling leaves

If you are unsure whether your plants are ready to be transplanted, take a peak below the soil’s surface. You can do this by gently massaging the seed cell from the outside, loosening the soil and root system. Then, turn the plant on it’s side and carefully pull the plant out of the cell.

If the roots are reaching the bottom of the soil, then you know your plant can be moved into a larger pot. This is the perfect time to up-pot tomato seedlings and prevent them from becoming rootbound.

With your plants ready to be transplanted, all that is left is to get your supplies together and make the move!


Choosing a Soil For Tomatoes

For planting tomato seeds, I recommend using a seed starter mix that is free of fertilizer and large pieces of wood. However, once they outgrow the seedling cells, the plants are ready to handle normal potting mix.

I recommend FoxFarm Happy Frog or Ocean Forest if you plan to use bagged soil. I recommend buying these from your local nursery or garden center, as online ordering is expensive and has become risky, with counterfeiters selling fake soil.

You can also mix your own soil using 1 part each of vermiculite, peat moss (or coco coir), and organic compost (like rotten manures and broken down kitchen scraps). This mix will be rich in nutrients from the compost, and will drain well and hold moisture.


How To Transplant Tomato Seedlings

Now comes the fun part. Moving your small tomato plants into a larger home is easy and quick, but only if you make the right preparations first.

Supplies needed:

  • Larger pots (I like these reusable 3.5″ plastic pots)
  • Potting mix (this is when you can switch to normal potting mix)
  • Mixing bowl or bucket
  • Water
  • Plant labels
  • Gloves (optional)

I like to work outdoors if possible, and hopefully you can find a warm day to get outside for your transplanting. The process can be a bit messy, as you are working with soil and moving plants from one home to another.

How To Transplant Tomato Seedlings

  1. Label pots.

    Always start by labeling the new pots into which your plants will be moving. This keeps you organized so you won’t forget which plant variety is which. Until the plants begin to fruit, you may otherwise be unable to tell the difference, as they look similar.Labeling tomato pots

  2. Pre-moisten potting mix.

    Pour enough potting mix to fill all the larger containers into a mixing bowl or bucket. Add water slowly and mix the soil thoroughly until it sticks together when squeezed, but does not drip water. This pre-moistening step helps the soil absorb water more readily.

  3. Fill pots about 2/3 full with soil.

    Add the pre-moistened soil to the larger pots where your tomatoes will be moving to. Leave about 1/3 of room at the top to add more soil after the transplanting.Preparing soil for transplanting tomatoes

  4. Dig a hole in the soil.

    Make a large indent in the soil to accommodate the tomato root ball. You can use your thumb or a stick to do this.

  5. Remove tomato plants from seed cells.

    Gently remove the tomato plants from their seed cells. It helps to start by gently squeezing the seedling cell trays from the outside, loosening the roots and soil within. After this, the plants should easily slide from the cells when turned on their sides.Tomato seedling root ball

  6. Move plant to larger pots.

    Make the move as quick and painless as possible! I don’t bother loosening the root system, as it seems to do more harm than good in my experience. If you got the timing right for transplanting your tomatoes, the roots won’t need any loosening. Place the plant roots directly into the prepared soil hole.Transplanting tomato seedlings into soil

  7. Add more soil around plant, burying stems.

    Tomato plants can easily form new roots along their stems. These are called ‘adventitious’ roots, and they can help young plants become established more quickly. It is safe to bury the stems by 1/2 inch or so when transplanting, and can actually benefit the plants in the long run. Fill the pots to within 1/2 inch of the surface of the pots, compacting until you feel slight resistance as you go.Berkeley Tie Dye tomato seedling

  8. Water and return to grow area.

    Give the plants a thorough drink of water, allowing them to drain, and then move them back to the grow area (under lights or in a sunny window). That’s it!

After your tomatoes have made the transition to their new homes, they will likely take a few days before continuing to grow larger. The roots need some time to settle in and adjust to the new soil medium.

Next Steps…

After your tomato seedlings are moved to larger pots, they will continue to grow much larger, and fast! Within just a few weeks, they should be much larger and ready to make the final move to the outdoors.

This will involve another transplanting, whether it be into the ground or into a larger final pot. I recommend using 3-5 gallon pots for growing large tomato plants. The process of moving outside is just about the same as moving your seedlings, only on a larger scale (more soil, etc.).

As your plants continue growing, you will likely need to prune, especially if you have chosen indeterminate varieties, as they produce sucker shoots that should be removed regularly.

Hardening Off Tomatoes

When you do make the move outside, don’t just pop them out into direct sunlight! The tender plants that have been growing indoors will surely end up burned by the intense light.

Learn more about hardening off tomatoes here >

Instead, slowly transition the tomato plants out into the variable outdoor elements. These include not just direct sunlight, but wind, precipitation and hungry wild animals. I like to start the process on overcast days or in the shade, and then slowly start to introduce increasing amounts of direct sunlight.

From indoors to fully acclimated outdoors usually takes 1-2 weeks. Hardening off can be started about 2 weeks before the plants will be moved outside permanently on warm days (above 60°F/15°C). Just don’t leave them out overnight if the temperatures are set to dip below this!

Fertilizer

Along the way, your plants will likely need additional feeding, as tomatoes grow fast and use a lot of nutrients. See here for a great list of recommended tomato fertilizers and how to properly feed tomato plants.

Essentially, younger tomato plants require plenty of nitrogen to grow lots of leaves and branches. After a month or so, I transition to a lower nitrogen blend and higher levels of phosphorus and especially potassium for big harvests.

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I hope this article helps you transplant your tomato seedlings at the right time, and with ease. It is a great way to spend time with your plants and care for them as they grow larger and mature. From here, you’re well on your way to bountiful harvests later in the season!

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