Potting sheds, windowsills and greenhouses should be fit to burst with young plants. In this month’s garden blog, we show you how to prepare your seedlings for their next important steps…
Seeds sown close together in seed trays will compete for light and water and will require more spacious surroundings to stretch their legs. Pricking out is when you transfer your small seedlings from their original compost and container to a slightly larger space.
The best time to do this is when you see the first or second set of ‘true leaves’ develop on your seedling. These can be found on many vegetable seedlings. A true leaf is a smaller version of the adult leaf. A seed leaf is oval and is the first leaf to emerge. Alternatively, look for white roots poking out of the drainage holes.
Choose the strongest seedlings to prick out. Fill a clean modular tray with our peat-free SylvaGrow® Multi-Purpose or John Innes compost and tap gently to settle. Make a hole at the centre of each module with a dibber. Each seedling will have its own module.
Most seedlings don’t like root disturbance. So gently hold the seed leaves and ease the seedling out with a pencil or dibber. Retain as much root as possible and try to avoid holding the stem, roots or true leaves.
The seed leaves are a handy marker for planting. You should replant your seedling with the soil level at the same level as the seed leaf. Firm in and water with a rose. Keep protected from the elements (sun, wind and cold weather) so the small plants have time to recover.
Our peat-free SylvaGrow® John Innes No.1 Young Plant Compost is perfect for pricking out seedlings thanks to its friable and free-flowing texture.
Once your teenage seedlings are beginning to outgrow their individual modules, it’s time to think about moving them on. Potting up is when you move semi-mature or small plants into bigger, individual pots (such as 9cm pots) so the roots have room to grow.
This is particularly important if for whatever reason you can’t get them into the ground straight away due to frost or waterlogging. Or, you want to grow on the plants in pots or grow bags. You can just transfer into bigger pots each time as the roots grow. A good indication that your young plant needs potting up is when roots begin to appear at the bottom of the pot.
It’s important that you only go one pot size up when you choose your container. A good way to test this is to place your smaller pot into the centre of the larger pot and check there is a thumb-width gap between them.
Your young plants will be more tolerant of being handled than seedlings but making the transition as gentle as possible really improves their chances. Place your small pot inside the larger pot again. Fill the larger pot with enough compost that the smaller pot sits level with the top of the larger pot. Then, fill the larger pot with compost around the edges. Take out your small pot to leave a hole that’s the perfect size for your plant.
Tap the bottom of the pot of your young plant, and ease the plant out gently. Hold it so the stem is between your fingers and the top of the root ball rests on your hand. Pop it in your pre-made hole and tap the pot gently to settle. Label and water. (Watch our video at the bottom of this blog.)
Our peat-free SylvaGrow® John Innes No.2 is perfect for potting on young plants, established houseplants and vegetable plants that will be grown in containers.
As the weather warms, you can start to “harden off’ your young plants. The best way to do this is to take them outdoors during the day and bring them in at night if frost or cold weather threatens. You only need to do this for around 10 days before the plants become acclimatised. But do keep one eye on the weather as even the sturdiest seedling won’t cope with a frost.
Another useful way to harden off plants is to put them in an unheated greenhouse or cold frame first – slowly opening the doors and vents a bit more each day.
Most young plants, whether bedding, perennials, or vegetables can be transplanted to their final spot around mid-May – complete with a healthy root system and strong growth, thanks to your earlier efforts.
Watch more of our gardening how-to videos on our YouTube channel.