Splitting cosmos seedlings

Pricking out and potting on

Growing plants from seed is one of the most satisfying things you can do in gardening. 

Growing from seed is also the most cost effective way to fill your garden with masses of new plants and it is incredibly easy too.

Anyone that has ever grown a few plants from seed knows the scenario. You buy a packet of seed. It’s got lots of little seeds inside, so you sow a few onto the surface of a top quality seed compost, cover over with a fine layer of more compost, water gently and watch as a carpet of green seedlings appear. It’s literally magic. 

sowing seeds in pots
Image: Martin Mulchinock

Then if you’ve done everything right, the pot quickly becomes congested with burgeoning young plants and you separate them into new pots and modules. This is called pricking them out and potting them on. It can be time consuming so there are a few tricks you can use to cheat.

One of the ways to reduce these tasks is to sow seeds individually into modules. Each developing seed then has its own space to develop and you don’t have to disturb it until its roots have filled the available space. It’s a great method for expensive or difficult seeds. If germination is in question then simply sow two seeds to a module and remove the weakest one if they both germinate, again this allows the stronger seed to develop within the module undisturbed.

Pricking out seedlings

If you sow seeds en masse you need to master the technique commonly referred to as pricking out. It’s a way of transplanting tiny seedlings into a pot or a module where they can grow on.

  • First you need to water the pot of seedlings until the compost is moist. This makes it much easier to separate them out. 
  • Next choose what you are going to prick them out into. Choose small modules or pots that will take an individual seedling and fill it with a quality compost.
  • Put your fingers, splayed over the top of the pot and gently invert the pot so that you catch the contents without squashing the seedlings. 
  • Now gently divide up the root ball of seedlings you’re your fingers and thumbs, taking great care not to crush the seedling stems. You should be able to divide the roots up into quarters. 
  • It’s easier to handle the root ball and work with this. As you gently divide the roots the seedlings should divide up too. 
  • You need to be able to gently pull away individual seedlings. Handle them only by the leaves; do not hold them by the stem, however careful you think you are being you will crush the stems.
  • Now using a dibber make a small hole in the compost inside a new pot or module and dangle the roots of the seedling into this. It needs to be planted at the same level it was growing at originally. 
  • Gently push a little more compost over the roots and then water with tepid water to settle the roots into place. 
  • Repeat with the next seedling until you have filled all the pots or modules. 
  • Place in a warm, light place to grow on. 
  • Once the seedling roots have filled the compost in the module or pot, which won’t take long, they can be potted up into a larger pot and eventually planted out into the garden when the danger of frost has passed. 
  • Keep the seedlings warm, in a light plants and well watered. 
seedlings growing
Image: Jean Vernon


To avoid the most common problems always use fresh, clean compost and clean pots and modules. Bring the compost into the greenhouse for a day or two to take the chill off it, so that it does not shock your plants. Water the developing seedlings with clean tap water to avoid passing on any fungal diseases that may linger in a water butt. Allow it to warm to greenhouse temperature before watering your plants. 

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