Propagation – How to grow seeds indoors?

Growing from seed means you can choose from a far wider selection of annuals, biennial and perennial plants than those found in your local garden centre. It is also very fulfilling and cheaper so you can grow more plants of the same variety; this is the best way of ensuring repetition and colour in your borders.

Growing seeds indoors allows more control then sowing outside and gives you a higher success rate in raising healthy seedlings.
I like to use 7cm black square plastic pots as you only want to grow a few seeds at once rather than sowing the whole packet of seeds in a tray: when they all come up at once you will not want that many and end up discarding them.

Seeds growingFirst make sure you use fresh compost and that all your pots have been washed (a disinfectant such as Jeyes fluid is perfect).
The growing medium I use for seeds is: 70% peat free/coir to 30% perlite (this prevents compaction and improves aeration/drainage).
Fill your pot with the compost to 1cm below the top of the pot making sure to firm down the compost, it is important the soil is level. Then put your seeds on top and finally cover with 1cm of vermiculite. A general rule is smaller seeds eg: Nicotiana (tobacco seeds) does not need covering with vermiculite. Always label your seeds with the name and planting date.

Potting compost with seedsAfter sowing, water the seeds well in a water bath then put in your propagator to germinate.

Check daily and remove condensation from the lid of the propagator.
As soon as your seeds germinate take them out of the propagator and move to a windowsill or greenhouse shelf out of direct sunlight.

Emerging SeedsWhen the seeds have produced the first adult leaves it is time to prick them out into individual pots.

Seeds are ready to be pricked out

Again, I plant up in 7cm pots. The growing medium I use for potting on is: 70% peat free/coir to 30% vermiculite with some added slow release fertilizer pellets.

Seedlings transplanted into pots

Just keep your seeds watered and when you can see roots emerging from the base of the pot, it is time to transplant into 9cm pots. Harden off in a cold frame for three weeks and then plant out in your garden and sit back and enjoy your efforts.

I am a qualified garden designer with a keen interest in contemporary, natural and traditional gardens. You can find me on Twitter  or like my Facebook page where you will find lots of tips related to gardening.

7 Responses to Propagation – How to grow seeds indoors?

  1. Jenny 2 March 2015 at 9:39 am #

    This is a great help for a novice. I have 2 queries – do you have to have a propogator or can you cover top of container with cling film ? once you have planted do they have to go in a sunny spot ?
    Thanks – Jenny

    • Nicky 2 March 2015 at 5:38 pm #

      Hi Jenny
      Thank you for your nice comments, in answer to your questions
      1. I wouldn’t recommend using clingfilm as it can cause high levels of condensation as an alternative a large freezer bag would be better and easier to remove the condensation every morning
      2. No, it is best to put the seeds in a bright place but not in direct sunlight

  2. Jane 2 March 2015 at 5:15 pm #

    Feel inspired now to go and buy some interesting seeds thank you

  3. Gabrielle 7 March 2015 at 8:45 am #

    Hi there! Thanks for such a helpful blog!!I have a hriybd seeds (F1) of Campari and temptation varieties of tomato but the problem is I have got no information about their growth habit, specifications and important dates (eg. of sowing, flowering, fruiting etc.). Do you have any idea about them? Would you like sharing it? If there is any good reference out there please guide me. Thanks.

    • Nicky 10 March 2015 at 7:23 am #

      Hi Gabrielle
      Thank you for your nice comments. I have never grown F1 Campari or Temptation varieties of tomato’s but I do grow F1 Sungold and would imagine that the germination is similar – they need to be placed in a propagator at a constant temperature of 18-20C (68-68f) until they germinate which takes around 7 – 14 days. Transplant the seedlings once the adult leaves have appeared into 9cm pots, when the plant has grown to 20cm high put in 23cm (9in) pots, growing bags or plant 45-60cm (18-24in) apart outside when the flowers of the first truss are beginning to open; plants for growing outdoors should be hardened off first. A very good reverence is the RHS ttps://

  4. Sean 22 March 2015 at 9:04 pm #

    Thank you for the very helpful seed planting advice.
    My problem is damping off of seedlings subsequent to potting on. This happened before Christmas. I disinfected all pots and all surfaces in the greenhouse but the seedlings are again starting to keel over. Any advice please?

    • Nicky 23 March 2015 at 10:07 am #

      Hi Sean
      The problem you have with damping off of your seedlings is caused by a fungi. This fungi thrives in a wet environment and usually occurs where you have excess soil moisture and particularly under levels of high humidity, poor air circulation and if seeds are sown to thick.
      To prevent this :
      1. Use uncontaminated soil mix (at the beginning of the year I would always use a new unopened bag of compost) – and make sure that your mixing area has been disinfected.
      2. Plant seeds in warm soil.
      3. Use a soil mix that drains well – I use a peat free compost with 30% perlite.
      4. Sow seedlings thinly to avoid crowding
      5. Use mains water if possible when watering seedlings. If using rainwater, ensure that the water butt is covered to prevent the entry of leaves and other organic debris that could harbour some of the damping off fungi. Do not overwater
      6. Keep seedlings well ventilated to reduce humidity
      Good luck with growing your seeds