Success With Seeds

LYIT Gardening Club gratefully acknowledges the generous donation of a large box of seed packets by Alcorn’s Garden Centre, Letterkenny.
These were distributed free of charge via the SU shop.
Students are encouraged to plant seeds in readiness for the first Plant Swap on March 20th
For tips on success with your seeds, please read on.

Seeds come in many shapes and sizes.  All plant seeds are dormant embryos.  Given the right conditions, they will germinate, i.e. they will sprout a root and one or two tiny leaves.  Different seeds have different requirements for germination.  But, generally speaking, all seeds need three things in order to sprout: Water, Oxygen, and Warmth.


It’s worthwhile investing in a good quality seed compost.  Good seed composts are sterilized and may have vermiculite or sand added to make the mix light and crumbly.  A lighter mix helps the seeds get enough oxygen and makes it easier for the first tender roots to push down easily.   Good seed composts are also designed to retain some moisture, but to drain off the excess.  It is for this reason that it’s vital that all containers, including seedling trays, have drainage holes on the bottom.  You will probably get better results from your seeds if you avoid using multi-purpose or potting composts.  They are generally not light enough and also they usually have additional fertilizers, which are too much for young seedlings.   If your compost is too compacted, or too wet, seeds will be oxygen starved and unable to germinate.

Water: Without water, seeds cannot germinate.  Moisture softens the hard outer shell of seeds. Some seeds don’t need much water to germinate, but others absorb more relative to their dry weight.  Before planting, some seeds need help to take up water

Chipging: Some seeds, e.g. Sweet Pea, Morning Glory etc., have hard seed coats which prevent moisture being absorbed by the seed. All that is needed is for the outer surface to be scratched to allow water to pass through. This can be achieved by chipping the seed with a sharp knife at a part furthest away from the ‘eye’, by rubbing lightly with sandpaper or with very small seed pricking carefully once with a needle etc.  You are only aiming to puncture the thin outer skin, NOT the seed itself.

Soaking is beneficial in two ways; it can soften a hard seed coat and also leach out any chemical inhibitors in the seed which may prevent germination. 24 hours in water which starts off hand hot is usually sufficient. If soaking for longer the water should be changed daily. Seeds of some species swell up when they are soaked.  If some seeds of a batch do swell within 24 hours they should be planted immediately.   The outer skin of the remaining (unswollen) seeds can be pricked gently with a pin and returned to soak for a while longer. As each seed swells it should be removed and sown before it has time to dry out.

Once water has been taken in, enzymes inside the seed are activated, which enable the plant embryo to use its stored food supply. Seeds contain just enough of that stored food to produce that root and unfurl the first leaf or leaf pair.  Be careful with water.   Too much water forces the oxygen out of the compost and seeds may drown or develop a fungus or mould and rot.  Insufficient water causes the tender seedling to dry out and die.  Moderation is key.  Watering should always be done from below, allowing the water to creep up through the compost until the surface glistens.

Oxygen: This enables the plant to breath.  Oxygen is present in soil in the tiny spaces between soil particles.  Use good quality seed compost, not potting compost.  Do not overwater or over compact the compost as this forces oxygen out .

Warmth: The temperature of the soil has a big impact on germination.  Most seed types have a fairly  specific temperature range that is ideal for their germination and this is usually listed on the seed packet.  In some cases, this is just above comfortable room temperature (16-24°C/60-75°F), and in others it is warmer still (24-32°C/76-90°F).  While the seeds may be tolerant within a range of a few degrees,  it is best to try to maintain a steady, not fluctuating temperature.  Fluctuating temperatures can damage a seedling in its critical early stages. You can control the temperature of the soil by using seedling heat mats, heated trays or propagators, or by simly placing your seed trays someplace that is reliably and consistently warm.  (not hot). If you have no way to heat the soil in your trays, or if you need to direct sow your seeds into cool soil, the seeds will take longer to sprout or may fail.

Cold: Funnily enough some seeds (lavender, roses, astrantia, violets, aconitum, alliums, panseys)

need a spell of cold  (usually a few weeks at  about 41F). to break their dormancy and “shock” them into readiness for germination .  For these seeds you need to fake the winter conditions that the seeds might experience if they fell off their parent plant in autumn and had to survive through winter before germinating when it warms up in spring.    One way to do this is to plant seeds in slightly moist compost in a tray or container, and then put the whole tray, sealed plastic bag, in the fridge  for 2 weeks or longer. The seeds must be moist whilst being pre-chilled, but it doesn’t usually benefit them to be actually in water or at temperatures below freezing.   The tray is then brought out into a warm place, and the seeds germinate as usual.  Light also seems to be beneficial after pre-chilling.  Any seeds that you pre-chill need only the lightest covering of compost, if any, over them.  The seed trays for pre-chilled seeds should be in the light and not covered.

Light: Light levels can also affect germination. Your seed packet instructions will usually tell you what is required.  Some seeds may require being started in a dark place with light excluded until the first leaf s appear.   Seeds needing dark for germination should be placed in total darkness.  Others, including pre-chilled seeds, may need to be sown on the surface of the soil and exposed to bright light. (e.g. poppies, lettuce).   Don’t place newspaper, brown paper etc. over the trays of any seeds needing light to germinate.


Sowing seeds  too deeply can cause them to fail. A seed has only enough food within itself for a limited period of growth.  If sown too  deeply it soon expends its energy and dies before it can reach the surface.   If in doubt sow shallowly.


The first pair of “leaves” are not true leaves.  The next set are the first true leaves.  Do not transplant seedling until you have 2-3 pairs of true leaves and a reasonably strong root system. When transplanting handle very carefully.  Tease roots out of compost by loosening underneath with a small tool.  Avoid handling the upper part of the baby plant but , if necessary, lift very gently by the leaves, never by the stem.

Seedlings probably need about 10 hours of light a day. Growing seeds on window sills may cause them to grow “leggy” and weak.  A “grow light” may be good investment.  A fluorescent bulb that can be suspended  or positioned  close to (about 4 inches above) the seedlings and moved upwards as the seedlings grow.    You can also set it up on an automatic timer.  There is separate file on grow lights available.

Keep temperature steady.   To avoid “damping off” and fungal infections, allow air flow, do not overwater and always add water from below.  (More on damping off at the end of this article.)

Harden plans off gradually by placing them outside for limited time each day , in good weather , before planting out in final location.  Sometimes a “cold frame”is used to harden off young plants. It protects them from heavy rain and strong wind as they get used to outside temperatures.  It may need to be opened on sunnier/warmer days.

Ferns (Garden and Indoor)

Fern spores usually appear on the underside of the leaves.  You can collect them by picking a leaf and leaving it spore side down on sheet of paper paper in a dry area with still air.

Germination of fern spores  is a little different from germination in flowering plants. The fern spore needs a fine film of moisture over which to “swim” in order to germinate.  Use a  peat-based compost. It can be pressed down more firmly and should be more moist than the  compost used for flower seeds.  The spores should be sprinkled closely together on the surface of the soil. Don’t cover the spores with soil but the container should be covered with a piece of glass and placed somewhere that is well lit but where the light is diffused.  It is essential to ensure that the compost remains moist at all times. Germination can take anything from 1 -5 months.  The first indication of germination is often the appearance of a film of green “ jelly” over the soil.  This would be a bad sign if growing seeds but it’s Ok if you are trying to germinate fern spores.

You may wish to try germinating the fern spore on blotting paper which is placed in a saucer and kept moist at all times.  Put a transparent cover over the saucer and put the whole lot in a well-lit (but not a sunny) position.   When you can see small plants appearing along the jelly the blotting paper should be lifted and placed on the surface of a container of compost and watered well.  It should then be covered with a transparent cover which can remain there until the plants are quite large.

Damping Off

Damping off is a fatal fungal disease can affect seeds and very young seedlings.  Usually, the plants will germinate and come up fine, but within a few days the stem and root tissues begin to rot. The baby seedlings  go mushy, fall over at the base, and die.  Sometimes a whitish “fur”  appears on the compost and or on the seedlings.  Damping off typically occurs if you plant old seed in cold, wet soil. Likelihood is further increased by poor soil drainage, high humidity levels, use of over rich potting compost, and planting too deeply.


  • There’s no real cure so prevention is key.
  • The biological fungicide Mycostop may also be used as a seed treatment to prevent seed or soil-borne diseases.
  • When starting seeds indoors, use seed compost – not potting or multipurpose compost.
  • Seed compost mixes should be  light and fast-draining with no added fertilizers.
  • Provide for good air circulation. Open the lid of the germination tray or use a small fan.
  • Have the soil surface near the top of the container to allow air circulation at the base of plants
  • Sow seeds thinly.  This prevents over-crowding which can lead to humid, moist conditions.
  • Water seedlings from below not from overhead.
  • Avoid overwatering seedlings.  (Forces oxygen out of the soil & creates too much humidity.)
  • Don’t water young plants in the afternoon.  The soil surface and the plants should be dry by dark.

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