Transplanting Seedlings

Garden Life
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Tips from Sarah the Gardener

Growing from seed can seem a little daunting, as it isn’t just a case of popping them in the garden and hoping for the best, like you can with store bought seedlings.  Sowing seeds is a process that gives a gardener plenty to do while waiting for things to warm up outside.

For the best start in life it is good to sow seeds into a seed raising mix. It is made of exactly the right mixture of ingredients that will help your seeds germinate successfully.

When seedlings first appear, they have a set of leaves that often look nothing like the leaves on the adult plant. These are called the seed leaves and contain the nutrients the plant needs to get going. The next set of leaves look more like what they are supposed to and are called the true leaves. These are normal fully functioning leaves that create energy for the plant from the process called photosynthesis. Once the first set of true leaves are big and strong, it is time to transplant the seedling from the seed raising mix with minimal nutrients, to a more nutritious mix.

The idea with transplanting is that you need to gradually move the plant into an ever-so-slightly bigger pot until it is time to move it into the garden.  This helps the plant to develop a strong root ball.  If you just put it in a large pot straight away you will end up with weak leggy roots.  Some plants like tomatoes may need to be transplanted up to three times before being planted outside.  An indicator a plant is ready to be transplanted is the roots begin to appear out the bottom of the container.

If a seedling is left in pots that are too small they can become root bound. The roots can be damaged or suffocated, which can lead to slowed growth and the plant won’t look very healthy.  This can also cause a check in the growth of the plant that can cause problems in the long term like plants bolting to seed prematurely or never reaching their full potential, resulting in a smaller harvest or being more vulnerable to pest and disease.

The container

The type of container isn’t so important as the plants will be in them for such a short time.  If you don’t have a collection of plant pots ready to use, you can improvise and upcycle the appropriate sized containers from your recycle bin.  Just so long as the container is clean and has drainage holes in the bottom.  

A good-sized plant pot to start with is about 5cm across for the first transplant, then move to pots about 10cm or even 15cm across before going into the garden.

The soil

Transitioning tiny seedlings into the garden is a bit like weaning a baby, you start with gentle mix and gradually strength it up so it is close to the soil the plant will encounter in the garden.  To protect tender roots from burning, a 50:50 mix of potting mix and compost is a good starting point.  Compost is okay to use by itself, or you could use compost and soil from your garden bed at a 50:50 mix. You could even just use the soil from the garden if you don’t have anything else, however it is best to avoid garden soil for the tiniest seedlings to reduce the risk of disease.

The process

Before starting, give the plant a good watering and allow the soil to drain.  Transplant shock can be avoided by using a seaweed tonic.  Then prepare the new pot by adding soil to cover the base so the roots aren’t exposed for longer than necessary.
Getting the seedling out of the soil can be a bit tricky.  IT IS IMPORTANT NOT TO HOLD ONTO, OR PUT PRESSURE ON THE STEM.  If the stem is damaged it can affect the way the plant grows and can be an entry point for disease.  Another part of the plant to be careful with is the growing tip.  If this is damaged the plant can stop upward growth.   It is ok to hold a plant by the leaves as they aren’t structural and if damaged or removed the plant will recover and continue to grow well.

If the seedling is in a tray with loads of seedlings, get a long thin object like a pencil or seed label and gently dig into the soil beside the seedling and while holding the seedling by a leaf, lever up under the plant to loosen and free the roots.

If it is in a multi-cell container you can push up from below – either by squeezing the cell or inserting a pencil into the drainage hole.  The root ball should rise out of the pot.

If it is in a pot by itself, put your hand across the top of the pot with the plant stem between your fingers and turn the pot upside down and give it a tap and the plant should pop out and then gently hold it by the root ball.