When to transplant tomato seedlings | 3 Easy ways to know

Transplant tomato seedlings when they have grown their second set of leaves and are at least 3-4 inches high. The second set of leaves are an indicator that the tomato seedling has established a strong enough root system to be planted out. Wait until the risk of frost has passed and the warmer Spring weather has arrived.

Transplant seedlings when the weather has changed in Spring. Some areas will get late Spring frosts so you may need to give them some protection if this is predicted. Frost can damage young tomato seedling leaves turning them white and causing sunscald.

For more on preventing tomato plants from being damaged by sunscald, check out my previous article here.

When to transplant tomato seedlings

Knowing when to transplant small tomato seedlings out into garden beds or pots is important to help them to thrive. Delicate seedlings that are planted out too soon can be damaged by frost, direct sunlight or their roots can suffer damage from the move.

1. When the second set of leaves grow

Tomatoes grown from seed will take 4-6 weeks to reach the size where they are ready to plant out. Buying seedlings from your local nursery is the easiest way to save time.

This year I have bought large seedlings which are around 10 inches high. These have their third set of leaves and large established root systems.

This is not necessary but will enable you to buy individual plants of a specific species which is great if you have a small space like me.

2. When the plant reaches 3-4 inches

Once a tomato plant reaches around 3-4 inches high it will have established a root system that will be equally as long. The stem will have strengthened up and the roots will be close to reaching the bottom of a small pot.

Most tomato seedlings will sold from nurseries in a punnet that has 6-8 plants. These will be sold when they are ready to be planted out into garden beds.

It is best to harden off the tomato seedlings by transferring them gradually into full sun. Move the plant out into the full sun for a few hours in the morning for 1-2 weeks. This will help the plant to adjust to the move into a full sun position and avoid sunscald.

Small 3 inch seedlings grow to 10 inches in a matter of weeks.

3. When the risk of frost has passed

Once the Spring weather has arrived and the chance of frost is lower, then tomato seedlings can be planted out into a garden bed or larger pot. For most areas this will be Mid-Spring however for sub-tropical climates this could be early Spring or even late Winter.

Pelleted chicken manure is perfect for newly planted tomato seedlings.

What happens if you transplant tomato seedlings too early?

Tomato seedlings that are planted out when they are too small might suffer root damage or wilt quickly. The plant could dry out quickly as it would have a less established root system. The delicate roots can easily be damaged when they are moved and the plant will not be able to absorb water or nutrients.

How long can seedling stay in trays?

Seedlings can stay in trays for 2-4 weeks after bringing them home. You will need to look after them well and they will survive better in a greenhouse. For tomato seedling that are 3-4 inches high and have grown their second set of leaves they will be fine to plant out straight away.

If you are planting the tomatoes in a full sun position and it is very warm, move them out into the direct sunlight gradually. You can start with a few hours each day for the first 2 weeks and then plant them out.

Slowly transition tomato seedlings out to full sun positions.

At what point do you transplant tomato seedlings to bigger pots?

Tomato seedlings in small trays of 6-8 can be planted out to bigger pots once they have grown their second set of leaves. It is best to choose a pot that is a few inches bigger to start with and grow the plant up to 10 inches.

I bought my tomato seedlings at this size and they were ready to plant out into my garden beds straight away.

Tiny seedlings planted out into large garden beds or pots do run a greater risk of pest attack, being stepped on by pets or people or becoming too damp and cold in the ground. A tiny seedling can be moved into a pot that is 4-5 inches across.

For more on the right pot size for tomatoes, check out my previous article.

When to transplant tomato seedlings | Summary

Transplant tomato seedlings when they are 3-4 inches high, have grown good sized second leaf sets and they are standing straight and strong. If you see the roots of the tomato seedling start to stick out of the bottom of the seed tray, they are ready to plant into a larger pot or out into your garden bed.

Plant tomato seedlings out in Spring to give them enough time to establish and grow ready for Summer. In regions with milder winters, you can even grow your seedlings in a protected spot outdoors. I had planted a seed in the middle of Winter and it is now a full size bush with flowers and it is only the beginning of Spring.

For cold regions you will need to wait for frosts to have passed before planting out new tomato seedlings so they don’t suffer sun damage.

Happy planting.