Pricking Out Tomato Seedlings – The Complete Guide

To successfully grow tomatoes from seedings, understanding when and how to go about pricking out tomato seedlings is important. 

Getting your timings right and following the correct procedures can help make sure that your tomato plants grow well and provide an abundant harvest of fruit later in the growing season. 

Why Is Pricking Out Tomato Seedlings Important?

Tomatoes that have been sown into a seed tray or propagator will be growing relatively close to one another, and in quite shallow growing medium. The young plants need to be moved to their own individual pots, filled with a rich and fertile growing medium that will support their continuing growth. 

If you leave them within a seed tray for too long as the seedlings grow, competition will be too great, root systems will not be able to continue to develop healthily, and the growth of the young plants can be significantly stunted. Damping off can also become a problem. 

It is important to prick out these young tomato plants at the right time, to avoid any check to their growth. And to make sure that their root systems can continue to grow healthy and strong. 

Note that pricking out will only typically be required where you have sown your seeds into a seed tray, and not from the beginning in their own individual pots. You can if you wish sow individual tomato seeds into individual pots or soil blocks from the beginning. But of course this will take up more space indoors at a time when windowsill/ propagator space may be at a premium. 

When To Prick Out Tomato Seedlings

Pricking out tomato seedlings is a job that you will typically get to in early spring, though it may be late winter depending on when you sowed your tomato seeds indoors. 

Tomato seeds can be sown at different times depending on where they are ultimately to be grown. 

Timing is important when it comes to pricking out tomato seedlings and it is vital not to undertake this job too early – nor leave it too late. 

Keep a close eye on your young seedlings. And prick them out as soon as they have developed their first pair of true leaves. Unlike the first two cotyledon leaves, these leaves will be shaped like the leaves you expect to see on a mature tomato plant. 

What Growing Medium To Use When Pricking Out Tomato Seedlings

Tomatoes that are pricked out of a seed tray should be potted on into their own individual containers or into soil blocks. 

There are a wide range of different containers that you might choose. For example, you might use old yogurt pots with holes pierced in the base of each one, toilet roll tubes or other bought or home-made biodegradable pots. Or you might use a soil blocker to avoid the need for small pots altogether. 

These containers should be filled with, or soil blocks composed of, any good quality peat-free multi-purpose compost. The mix should be moist, rich in organic matter and fertile – to give the tomato seedlings what they need to continue to grow well. 

How To Prick Out Tomato Seedlings

Once tomato seeds have germinated and tomato seedlings have two true leaves above the cotyledon leaves:

Before you start pricking out seedlings, it is a good idea to gather everything that you will need. You don’t want to have to put everything down to find other elements once you begin. 

Fortunately, you don’t need a lot to get this job done. You will just need:

• Containers or soil blocks in which to place the seeds that you are pricking out. 
• The growing medium for those containers, or to create the blocks. 
• A delicate tool that you can use to gently lever the seedlings from their current growing positions. And perhaps another tool to make the holes in which to place them. 
• Labels (to keep track of what all your seedlings are) and something to write on them. 

While you are pricking out seedlings, it is also handy to have access to water so you can rinse your hands between times, as you might want to label up some seeds before you prick out some more. 

The process itself is very simple:

• Step One: water the seedlings around an hour before pricking out to make the process easier, and lessen transplantation shock for the young plants. 
• Step Two: Make a hole in the growing medium in new pots or soil blocks in which to place the seedling you prick out. (Two tools are traditionally used in horticulture for pricking out procedures, widgers and dibbers. Widgers are shaped like a very thin trowel or spatula and are often used to lift out seedlings without damaging the roots. Dibbers are thin, pointed, pen-like tools used to make holes, and sometimes to firm in seedlings when pricking out. However, I would certainly not say that these tools are essential for new gardeners. You can make do perfectly well without them. I usually use a small wooden stick (a lolly pop stick could work just fine) for pricking out, both for easing up the seedlings and for making the holes. You might also use a small spoon and a pencil – or other small implements that you have lying around.)
• Step Three: Grasp a tomato seedling gently, holding it by the leaf rather than the stem. It is best to hold the seedling by a leaf because if you do accidentally break a leaf, this won’t kill the plant, but if you break the stem it is usually game over. 
• Step Four: Using the tool you have chosen for pricking out, ease the seedling out of its current position. Take care to keep the roots in tact. 
• Step Five: Gently lower the pricked out seedling into the hole you have prepared. Aim to bury the stem of tomato seedlings to just below the lowest leaves. Gently firm the growing medium around it, and water it in gently. 

When To Transplant Tomato Seedlings

The tomato seedlings that have been pricked out and potting up into their own individual containers or soil blocks, they should be grown on indoors and the hardened off before they are transplanted into their final growing positions in your polytunnel or greenhouse, or outside in your garden. 

During this period, you need to keep the growing medium moist, but avoid overwatering. You also need to provide well-lit conditions to prevent the tomato seedlings from becoming leggy. (For earlier sowings, grow lights may sometimes be required, or at least beneficial for young tomato plants.)

It is also important to make sure that the temperatures in the location where your tomato plants are situated remains at or above 16 degrees C. 

After around a month, typically when the first flowers open in your tomato plants, these can be transplanted into their final growing positions. But these should be hardened off first to acclimatise these indoors-grown plants to outdoors growing conditions.

Tomatoes can be planted out a little sooner if you are growing them in a polytunnel. But wait until conditions have warmed reliably before you plant out tomatoes in your garden. 

References:

https://www.ruralsprout.com/how-to-prick-out-seedlings/

http://www.oakleafgardening.com/glossary-terms/dibber-and-widger/