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potting on seedlings

Pricking out

Pricking out seedlings after they have germinated is necessary for healthy plant growth. Follow our guide and share your favourite plants with friends and family.

On this page

  • About pricking out
  • What to do
  • Five plants to try

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About pricking out

Pricking out is an essential part of propagating plants sown in seedtrays. Once seedlings have germinated, they need space to establish a strong root system. It’s important to prick out as soon as the plant is ready which is usually when the first true leaves emerge (ie the second set of leaves that emerge after the seed or cotyledon leaves). This isn’t always true in the case of large seedlings like courgettes which may need pricking out before the true leaves appear.

What to do

How to prick out

  • Prepare a cellular seed tray or individual pots with good potting compost and firm in well. Ideally the tray should be 7.5cm (3 in) deep to allow for the development of a strong root system.
  • Water the compost so that it’s just moist and using your finger or a dibber, make a hole that’s wide and deep enough to accommodate the new plant.
  • Choose the strongest seedlings as weaker plants are less likely to survive transplanting.
  • Gently holding onto the seed leaves, use a dibber or pencil to ease the plant out of the compost, retaining as much root as possible.
  • Always lift your seedlings one at a time and never hold by the stem or roots, as you can easily damage the plant.
  • Resting the roots on your dibber, transfer your seedling to its new position.
  • Lightly firm in the soil around the plant with your dibber, making sure the seed leaves are just above the level of the compost.
  • Transplanted seedlings should be placed at least 3.7cm (1.5 in) apart.
  • When you have finished pricking out your seedlings, water them in using a fine watering rose and place them on a windowsill where they will keep warm and receive adequate sunlight.

Pricking out Gardening Guides from BBC Gardening

Potting on seedlings

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Pricking out seedlings

When seeds germinate the first leaves to appear are the cotyledons or seed leaves. These are usually a pair of oval, fleshy leaves that bear no resemblance to the mature leaves of the plant.

The conventional advice is that seedlings should not be pricked out or transplanted until the first true leaves appear, but the gardener must exercise common sense and move them on only when they are large enough to handle.

In the case of large seedlings, such as Courgettes or Marrows, this could be before the true leaves have developed and it is sound advice to sow such subjects individually in small pots.

Removing tiny seedlings from the sowing container into trays of a good universal compost can be a delicate business. The golden rule is never to handle the plants by their stems, which bruise easily, but always by their seed leaves. Some people use a sharpened or tapered piece of wood, such as an ice lolly stick, or a metal device called a widger to separate and ease out the seedlings, taking care not to damage the delicate roots.

Invariably there will be more seedlings to transplant than available trays to accommodate them, so some will have to be sacrificed, given to friends or put into the compost bin. The important point is to give the transplanted seedlings adequate space to become sturdy young plants.

As a rough guide, allow about 50 seedlings to each full size tray.

It is good planning to prepare the planting holes in the trays of well-moistened compost before you actually lift out the seedlings from the sowing container. Simply ease each seedling into position with the roots falling neatly into the hole, then gently firm the compost into contact with the baby plant while still holding it by the seed leaf.

Proprietary composts contain enough plant food to give the pricked-out seedlings a good start in life, but you can, if you wish, start feeding with a dilute liquid fertiliser, such as Maxi-crop, Liquinure or Phostrogen, after a couple of weeks or so.

Hardening off seedlings

Half-hardy annuals, half-hardy perennials and some vegetable seeds have to be germinated indoors because they would be damaged by frost, harsh winds or cool growing conditions.

They are sown early in the year in a heated greenhouse, propagator, warm room or even, to start off, in the airing cupboard. Most seeds need a minimum temperature of 65F (18C) and will tolerate a drop overnight to about 50F (10C), but there are exceptions and they are dealt with separately.

Once the seedlings emerge they must be given plenty of light, although not direct sunlight, until they are large enough to be pricked off into trays (see pricking out above).

The final operation before planting out is to harden off the young plants. The idea is gradually to acclimatise the seedlings to the harsher conditions of the great outdoors. Allow a minimum of ten days to do this, preferably longer.

Start by putting the trays in a sheltered position outdoors for two hours during daylight and lowering the temperature of the greenhouse or propagator for the rest of the day. Slowly increase the period that the plants are outside so that by the time the frosts are finished, the plants are fully conditioned to being outside. Don’t forget that the trays will need watering but should be protected from heavy rain.

When the young plants are transplanted to their flowering positions they may still need some protection against the damaging effects of strong, cold winds.

A very useful aid to successful hardening off is a cold frame. It should be large enough to accommodate all the seed trays, but can be a very simple inexpensive structure. During the day the lights – that’s the glass or plastic cover over the walls of the frame – can be opened or removed altogether, but put back into position overnight.

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Advice and information on how to prick out and harden off your seedlings