Sowing and Transplanting

Sowing Seeds

  • Always buy good quality seeds, organic if possible. Seeds are perishable – store them carefully, if possible in a sealed tin somewhere cool and dry. Keep an eye on the “sow before” dates on your seed packets – old seed generally will not germinate as successfully as new seed.
  • Seeds can be sown: directly in the ground (known as “in situ”). Or in a pot, seed tray or seed module (a tray with individual compartments or “plugs” in it) and transplanted later
  • With the exception of carrots, parsnips, potatoes, onions and garlic, you are better off to sow seeds in pots or trays and then transplant them out in to the soil later. This is because plants are at their most vulnerable (to frosts and slugs for example) when they are seedlings and it is generally more successful to plant a plant rather than a seed! Sowing seeds in pots/trays allows you to get a head start on the growing season as you keep the pots/trays indoors or under cover during Feb/March/April when it is generally too cold to sow outside.
  • Before you start to sow seeds, thoroughly clean all the trays and pots that you used last year as they may well be harbouring disease.
  • Potting compost is the medium that is used to sow seeds in. Potting compost is a sterile medium which means you know there are no weed seeds in it. It also retains moisture very effectively which is important for your seeds. Interestingly, potting compost is very low in nutrients so it is only ever used for starting seeds off – if you intend to grow a plant to maturity in a pot, it will need to be transplanted in to a medium that has more nutrients in it (e.g. a mix of compost and soil etc). Seeds do not need to sown in a medium that is rich in nutrients since they already have all the nutrients they need for germination. It’s worth buying good quality potting compost. Be wary of special offers that appear to be too good to be true – they generally are and will result in low germination rates! You can now buy organic and peat-free composts.
  • It’s very important when sowing seeds to sieve the compost first – you can buy a garden sieve for this purpose in most garden centres. The reason we do this is that if there are larger clumps of compost, smaller seeds might fall down through the cracks and fail to germinate because they’re too deep in the compost. Sieving the compost to a fine consistency prevents this from happening. Fill the pots/trays with the sieved compost leaving about half an inch at the top to allow for watering. Bang the pot/tray against the table a few times to help the compost to settle down in to the container.
  • Sow the seeds carefully based on instructions on the seed packet. With some vegetables you can sow several seeds in each pot or in each module in a module tray. With others you sow only one.
  • Keep the potting compost moist – this is crucial, particularly when you are waiting on seeds to germinate. Many GIYers cover their pots/trays with cling film or plastic covers (recycled plastic punnets work well for this) which retains moisture and reduces the need for watering. Remove the covering as soon as the seeds germinate. Some seeds require higher temperatures than others to germinate. Check on the seed packets. Do not let the seedlings dry out, but don’t over-water either! Be consistent with your watering regime. When watering small seedlings use a fine rose head on your watering can – the water comes out in a fine mist.
  • Seedlings will need plenty of light to thrive – keep them on a sunny windowsill. A common problem for GIYers is that they sow seeds to early in the year (Jan/Feb) when there is very little light by day and the seedlings become “leggy” (long and thin) as they are basically reaching for light. Some seedlings (tomatoes for example) will do better if they have a heat source beneath them – you can buy a heating mat or pad which you put the pots/trays on top of. These work well but be careful that the heat doesn’t cause the compost to dry out.
  • Once seedlings emerge, gently stroke your hands over and back through them every day – this mimics the action of the wind and encourages strong root development.
  • As mentioned above there are some exceptions to this sowing/transplanting regime. With potatoes for example you sow “seed potatoes” – which are basically small potatoes. With garlic you sow the individual cloves (each one becomes a bulb), while onions are generally sown as “sets” (basically baby onions). Carrots and parsnips are also generally sown direct in to the soil because they don’t transplant well. Given the tiny size of carrot and parsnip seeds, it goes without saying that the ground needs to be well prepared in advance. Dig and fork it over to break up the large clods of earth and then rake to a fine tilth – the sowing area should be completely flat and the soil should be a fine, crumbly consistency. Mark out rows 28 inches apart using a hoe or the end of a trowel – sowing in rows like this means that you will know which are seedlings (and which are weeds) when they germinate. Sow the seed thinly (with carrot seeds this means about 8-10 seeds per foot). Cover the seed carefully with a hoe or rake, firm gently and then water them.

Hardening Off

If you move your seedlings from a lovely warm room to a cold veggie patch outside, they will probably never recover from the shock! “Hardening off” is a process whereby seedlings are acclimatised to the temperatures and wind outside. It involves moving your seedlings outdoors for about a week before transplanting. Start with a few hours outside and increase the amount of time each day. Put them somewhere relatively sheltered and sunny and don’t forget to bring them back in!

Thinning Out

Thinning out is a process whereby you remove and discard some seedlings to make sure the seedlings that remain have enough space, water and nutrients to thrive. It generally only applies to seeds that are sown directly in to the soil – with seeds that are transplanted from a pot/tray they will generally be transplanted to the correct spacing (as outlined on the seed packet) so they won’t need thinning out. Equally, with seeds that are sown direct in the soil, if you sow very carefully and thinly in the first place it reduces the need to thin out. When thinning seedlings, remove weaker looking plants.


Transplanting is where you move the seedlings to their final growing position outside following the period of hardening off. There is no hard and fast rules about when is the right time for this as it varies from vegetable to vegetable. Check the seed packet for more information. In general though you want to transplant before the seedling outgrows the pot/tray they were germinated in. If this happens they become starved of water and nutrients and may never recover. With module trays you can generally check underneath to see if the roots are starting to appear through the holes in the base – if they are, it generally means they are ready to be transplanted.

Water the seedlings well a few hours before transplanting – this will make it easier to remove the seedling from the pot/tray without disturbing the root.  With a module tray you can generally pop the seedling out from beneath with your finger – do so carefully. You want to minimise disturbance to the root of the seedling. Ideally you want to bring as much of the potting compost that the seedling grew in with you. Make a hole where you are going to grow the plant (slightly larger than the plant) and then pop the seedling in carefully. Fill in with soil and firm in gently – some seedlings (like cabbage and other brassicas for example) like to grow in very firm soil and therefore need very thorough firming in. Water the seedling well.

Keep an eye on your seedlings – they are very vulnerable at this stage in their development. Protect individual plants from very cold weather and slugs using small “cloches” (you can use a plastic bottle cut in half for this if you wish).

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