The Gardener's Almanac

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Seed Sowing - Indoors



Decide what you want to grow then consider "do you have the facilities to grow them?"


Establish if what you want to grow is hardy, half hardy, biennial or perennial plants, this will determine which varieties require heat.


Decide on how many plants of each variety you require, there is not much point in growing more than you require.


Establish when you are going to sow your seeds.


Note: later sowings reduce the caring period prior to planting out.


Sort out your seed packets in order of sowing.










Consider your source of heating, e. g. Hotbed, Propagator, Windowsill, Airing cupboard.


Note; the more half hardies you grow the more heat you will need.


Establish where you are going to put your seedlings to harden off until planting out time. e.g.


Cold frame, Cool greenhouse or Conservatory.



Click here for more planning information.





Click on description to start slide show;





Full trays


Half Trays


Quarter Trays


9 Cell inserts


12 Cell inserts


25 cell inserts


42 cell inserts

















Containers can take many forms, e.g.


Pots, half pots (pans), flat trays, cell tray inserts and plug trays of various sizes, and / or recycled food containers.


In recent years, cell/ plug trays have become quite popular particularly by commercial people when sowing seed.


Note; To reduce the risk of diseases being transmitted to the new seedlings, ensure that the container/s used, are clean.



The Pro's for using cell trays;


Sowing seed in individual cells can be time consuming, but one will find that this method will save time in the longer term, for example;


  • At the pricking out stage, they are effectively already pricked out.


  • There is less root disturbance when potting up.


  • The plants tend to grow faster because they have not been ‘checked’ at pricking out stage.


  • Indirectly this helps in other ways, i.e. one can sow later and save heated space, or earlier, and put them in the cold frame sooner.


  • You only sow sufficient for your needs.






Use soilless seed compost or multi purpose compost with added silver sand as shown in the following example;

Seive compost if required In this example the mix is 2:1 Finished product.


Note; Too high a fertiliser content at this stage could be detrimental to the seedlings.


Click here for more information on compost.





Seed Sowing;


As a general rule seed can be considered to be of four sizes; Dust - Small - Medium - Large, consequently this gives rise to at least four ways of sowing;



Sowing dust sized seed;


Select a plug tray with 12mm x 12mm cells and seive seed compost into the cells.


Note; Sieving the compost aids filling the cells and is a better medium for the fine root system.


Tap the tray on the bench to settle the compost to the bottom of the cell.


Alternatively; fill a pot/pan/tray with sieved compost and tap it on the bench to settle the compost.



Mix the seed with a teaspoonful of ‘dry’ silver sand together in a salt shaker, then shake the contents onto the surface of the compost.


Alternatively; add the siver sand to the seed packet and shake it well to mix the sand and seed together, then sprinkle the mixture onto the surface of the compost.


As a general rule ‘dust’ sized seed do not require covering with compost i.e. they are sown on the surface and in this case the sand will give all the covering that is required.




Sowing small/intermediate size seed;


These seed are generally too large to use the ‘shaker’ method or too small to use tweezers.


Prepare compost as described above, substituting 25mm x 25mm cell trays for (12mmx12mm) then;


Place a pinch of seed in each cell of the cell tray and lightly cover.


If using a pot/pan/tray spread the seed thinly over the compost and lightly cover.




Sowing medium sized seed;


Select a plug tray where the cells are 35mm x 35mm and fill it with seed compost to within 6mm (¼”) of the top of the cell, tapping it as described before.


Sow individual seeds one to each cell and lightly cover.


Place on surface of compost with tweezers taking care not to squeeze or damage the seed.


An alternative is to place two or three seeds to a cell, then pull out all but the strongest seedling after germination.


If growing in a pot/pan/tray, fill it with seed compost to within 6mm (¼”) of the top of the container, tap it as described before, sow the seed thinly on the surface of the compost, and lightly cover.




Sowing large seed;


Select a plug tray where the cells are 50mmx50mm and fill it with seed compost to within 12mm(½”) of the top of the cell, tapping it as described before, then follow the procedure as described in ‘Medium’ sized seed.


Alternatively; Pick up seeds with the fingers and place on the surface of the compost.


Ditto if using a pot/pan/tray


Note; Quite often large seeds are flat so it it is best to sow them on edge into the compost.






Some varieties of seed may require a light covering of compost to assist germination this is best done by riddling/sifting the compost over the seed.


Other varieties may require light to germinate, meaning they have to be sown on the surface of the compost.


To prevent movement of seed sprinkle a thin layer of Vermiculite over the seed to hold the seed in place until they germinate.



Depending upon your source of heat, place the tray/pot in a polythene bag and place it in the airing cupboard.


Put a sheet of glass over the tray/pot and put on the hot bed.



If using a purpose made propagator place the tray/pot in it, then replace the lid.


In each case; clean off all surplus condensation daily from the bag/glass/cover.



As soon as seeds germinate remove the covering and place the container where it gets plenty of light (but not direct sunlight) and maintain a temperature of 5-10C (40-50F).


Remove seedlings from propagator and place on hot bed to grow on.


Turn the containers regularly to prevent seedlings becoming draw and lopsided.




Stratification; Many shrub seeds require stratification; this means the seed is subjected to a cold period.


To do this; seeds can either be placed in the fridge* in their packets to chill prior to sowing.


An alternative method; is to firstly sow the seeds into a suitable container then place the container into a plastic bag which in turn is placed into a fridge*


The purpose of this procedure is to simulate the cold frosty periods they would be subjected to in the wild.


* Not freezer or freezing compartment.






There are a number of methods to water seed trays, for example;


  • Use a fine rosed watering can to apply the water prior to sowing the seed.


  • Use a fine rosed watering can to apply the water after sowing the seed.


  • Place the seed container in a bowl/tray of water ensuring that the water does not rise above soil level, and allow the water to seep through the compost until it is thoroughly wet.


This is distinguished by the darkening of the compost surface.


This method can be used either before or after sowing.


  • Another useful method is, fit a nozzle from a mastic/silicone tube to a small watering can in lieu of the rose.


This allows better control when watering individual plants, and eliminates the over-spray you get from a rose.


It is also useful after pricking out, as it means one can water the soil around the seedlings without touching the leaves, thus reducing the chances of ‘damping off’


  • Another quite useful technique to prevent 'damping off' is to occasionally spray the leaves of cuttings & seedlings with a hand held spray gun filled with a solution of clean water and a proprietary fungicide.




A few Tips;


Use square pots rather than round ones, they take up less space when full (or empty), and when it comes to watering there are no gaps between pots as there are with round pots.


When sowing seeds in trays, use ‘quarter trays’ (160x90mm) or divide half trays into two, or full trays into four by means of a plant label/s or a piece/s of split cane.


This saves on compost and heated space.


Click here for sowing outdoors.



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Copyright © Updated 2011