Repotting Rock Wool Seedlings

Introduction

Step By Step Video

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Video Transcript

In a previous video I showed how easy it is to sow seeds using rock wool cubes. Rock wool is a mess free way of planting seeds, just pop the seeds into the rock wool, and about 7-14 days later you should have tens of seedlings for replanting. There’s no need to get hands dirty, and sowing is very fast.

The rock wool growhouse has a reservoir beneath the rock wool cubes. This ensures the cubes never dry out, and can be filled with diluted nutrient solution to grow on the plants. Plants grown hydroponically developing long roots that spread into the water tray.

However, I prefer to transplant the seedlings very soon after germination when the roots are still small. One of the great advantages of germinating with rock wool is that there is almost no risk of damaging the roots during transplanting.

When lifting the cubes out of the container, the roots are sometimes visible through the rock wool.

I think the fastest way of transplanting, and to minimise any shock to plants, is to prepare the soil and pots before dropping in the rock wool cubes.

Using a large tub, pour in some shop bought compost - shop bought compost should be weed free. Rubbing the dry compost between the palms of your hands helps separate any lumps. The next step is to thoroughly wet the compost. This avoids the need to water in the seedlings, which can sometimes damage the stems under the weight of the water. On this mix, the soil was still a little dry, so I added some more water and mixed again.

An alternative to shop bought compost is to use coco bricks, sometimes called coir bricks. Coir bricks are lightweight, convenient, and mess free, but will require nutrients to be added when hydrating. I hope to make another video about growing with coir bricks.

The earth should now be nice and wet, and ready to be used to fill the pots. To ensure there are no air gaps in the pots, I filled them with compost and then used the back of a pot to push in the soil. If need be, top up with more compost. The advantage of using a big tub is that no compost spills anywhere, and filling the pots becomes a quick and easy process. I filled the pots to about one centimetre from the top of the pots.

Before transplanting, prepare seed labels to help distinguish plants. I write the labels using pencil, as this is easy to rub out and reuse each year.

Potting a seedling is now a very simple process. Use a stick, the back of a pencil, or similar to create a rockwool cube sized hole in the compost. The cube is simply dropped into the hole. I firm the soil around the cube to make sure that there are no air gaps. The great benefit of this method is that there is no disturbance of the roots, and there is no risk of damaging the stems of the seedling. There is no need to water the seedling after planting - I deliberately choose not to do this to avoid damaging the seedling.

After all the seedlings are transplanted, I place them on small plastic trays. The plastic tray helps to reduce mess. The trays capture any surplus water that seeps out of the compost.

I usually grow on the seedlings on a sunny windowsill for two to three weeks. When the seedlings have developed their true leaves, like this tomato plant, they are ready to be grown on in a greenhouse or polytunnel.