Greenhouse Gardening – Terminology: Pricking Out and Potting On

The term 'pricking out' refers to the transfer of seedlings into more spacious growing conditions, which gives them the scope to develop into young plants. Once germinated seeds are about to develop their first true leaves – as opposed to their initial 'seed-leaves' – they should be lifted from their seed tray (also called a flat) and planted in a hole prepared in the compost of another tray or in a small (no more than three inch) pot. The way to decide which get potted individually and which are to go into larger trays is to see if the seedlings are to be thinned again – if they are annual flowers or lettuce or other crops, you will probably need to take out the weaker plants in a couple of weeks time and in this case they should be planted I trays. If they are not to be thinned, because they are specimen plants or individual vegetables like peppers or tomatoes, plant them in pots. In trays, seedlings should be planted in straight rows around two inches apart, giving them room to grow without having to compete for space or light.

Once each tray is full, it should be watered carefully, using a fine rose on the watering can to settle the compost around the young roots without disturbing them. In the first few days after pricking out you will need to check if the seedlings require watering, and it's a good idea to offer some shading to protect them while their roots grow. Once they have become established the shading should be removed to give them the best light.

Potting on is the system of offering a container grown plant a new growing medium – always remember that your intention is to grow a large plant in a small pot not the other way around! Large plant/small pot encourages the growth of a good root network. One tip that leads to successful potting up is ensuring that plants are never removed from dry soil - so soak the seed tray or pot thoroughly and leave it for an hour or two before you make the transfer, making sure that you keep the root-ball intact. With older style clay pots which had only one hole in the base, it was essential to put a few stones or pieces of broken crock in the bottom to improve drainage before filling with compost. The density of firming down depends on the plant being potted. Winter-flowering begonias for example do best with light firming, while pelargoniums, and hydrangeas prefer a more firm base, while the majority of woody shrubs like fuchsias need their compost to be highly compacted to do well.

Greenhouse gardening potting on photograph by liz jones 112 , used under a creative commons attribution licence