Pricking Out Seedlings
Pricking out seedlings is an essential part of propagating plants, particularly those sown in trays of seed compost as this growing medium is generally devoid of nutrients.
To remedy this the seedlings require transplanting (pricking out) into a compost with more nutrients in it; e.g. potting compost.
As soon as the first* set of true leaves appear (ie the next set of leaves that emerge after the seed or cotyledon leaves) the seedlings should be transplanted.
*This is not necessarily the case for all seedlings, the seedlings of many curcurbits e.g. courgettes may need pricking out before the true leaves appear.
Pricking out can be a tedious task, however, with the aid of cell trays, as discussed in seed sowing this task can be somewhat reduced.
What is being grown often determines what type of container the seedlings will be pricked out into.
Generally the larger the plant the larger the container required, however do not be tempted to prick out into what eventually will be the final pot size.
It is much better to pot on plants as they outgrow their initial container/s.
The most common types of containers are: trays, boxes, punnets, cell trays and pots.
In each case fill the container with moist compost, prior to pricking out.
Do not over compact the compost in the container, it is better to just fill the container to its brim, then tap the container on the bench.
This should give all the compaction that is needed.
It can be an advantage to form a planting hole in the compost at this stage in preparation to recieve the pricked out seedling.
Most experts will advocate that you should select the strongest seedlings as weaker plants are less likely to survive transplanting, which is a fair point!
However the smaller seedlings in the batch may not necessarily be weaker, they may be, as in the case of some flowers just a different colour or have some other different attribute.
Meaning that; ignoring this point / suggestion could potentially lead to missing out on something special, the choice is yours!
But yes! generally prick out the healthiest looking seedlings.
Seedlings ready for pricking out
Gently hold seed leaves between the index finger and thumb of one hand,and by means of a dibber in the other hand, ease the seedling out of the compost, retaining as much rootball as possible.
Always lift your seedlings one* at a time and never hold by the stem or roots, as this might bruise the stem of the plant.
Such bruising/damage may lead to fungal disease (damping off)
Insert seedling into pot
Inserting seedling into pot
Water in seedling
Labelled and ready for growing on
* An exception to pricking out singly would be when pricking out plants like lobelia.
In this case, due to the minute size of the individual seedlings, you would prick out a few at a time (a cluster)
Transfer the seedling / cluster to the pre-filled container.
Lightly firm in the soil around the plant with your dibber, making sure the seed leaves are just above the level of the compost.
Once the seedlings have been pricked out carefully water* them in, using a fine rose or a fine nozzle on the watering can.
* Some people advocate that you should water the compost prior to pricking out which is fair comment.
However the writer feels that by doing it after pricking out, the fines in the compost will be washed down into any cavities that may have been left by the pricking out process.
This means that the grower can be more assured that the whole root system is in contact with the compost, whereas the pre-watering method may leave voids in the compost.
Fine Nozzle method
Keep the seedlings shaded for a couple of days to allow them to recover.
Be careful not to over water them at this stage, remember these are tiny plants and there is a limit to the amount of water they can take in at this stage.
Once they have settled in introduce them to a slightly cooler well lit area, but not into direct sunlight*.
*The sun's rays are magnified through glass (even winter sun) and this can scorch the young leaves.
Water as necessary.
If pricking out relatively small plants, aim to give each plant around 40-50mm (1½"-2") growing space between each other.
The use of celled insert trays goes a long way to ensuring this, and is also very useful when potting on, or planting out, as it avoids damaging the root system of adjacent plants.
For example; use standard 14”x 8” (450mmx 200mm) cell tray inserts with 15 or 24 cells per tray.
Pricked out Seedlings
For larger plants, prick out into suitable sized pots or large celled trays.
If pricking out plants for friends, prick out into punnets / strips.
If pricking out structural plants destined for containers, prick them out into 3” (70mm) square pots from the outset.