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Success with Seeds

Back to basics with seeds!  Don't let past failures put you off - read our refresher course on seed sowing for growing success!


Chose good quality seeds from a reputable supplier - preferably organic.  Store your seeds in a cool, dark, dry place for best results. Remember to read the instructions on the back of the packet regarding sowing dates. Keep an eye on the use by dates of your seeds - most will keep for several years but there are exceptions as the following list shows:

Viability of common veg seeds -

1 year   -  onions, parsnips, parsley, spinach
2 years -  corn, peas, beans, chives,
3 years  - carrots, leeks, asparagus, turnips, swede
4 years  - peppers, chard, pumpkins, squash, watermelons, basil
5 years  - most brassicas, tomatoes, cucumbers, celery,lettuce,chicory

As a general guide the following seeds are best sown inside with heat starting in February - Tomatoes, Peppers, Aubergines, Early Cabbage, Calabrese, Lettuce, Cucumber, Melon, Celery, Courgette, Pumpkin.  Seeds that are best sown outside in seed beds, modules or direct -  Parsnip, Broad Beans, Radish, Leek, Onion, Cabbages, Peas and Beans, Carrots, Beetroot, Spinach, Lettuce, Turnip/Swede


  • For every vegetable there is an optimum soil temperature for germination, and at that temperature the maximum number of seeds will germinate and in less time than at any other temperature. Long germination times also make the seeds more vulnerable to disease. A good guideline figure that suits the majority of vegetables is 20°C. But take note that there are upper temperature limits for certain crops -

Lettuce will not germinate at temperatures above 23°C
Leeks and onions will not germinate well above 21-24°C
Celery germinates best between 10-19°C – much higher and it won’t come through.

  • You can warm up the soil outside by a few degrees if you cover it with ground cover.
  • A soil thermometer will give you an accurate soil temperature figure. A warm day does not mean warm soil.
  • Beware a sunny day when propagating in the greenhouse. Temperatures can soar, basically cooking your seeds or seedlings.
  • If you need a bit of heat to get things started then you have several options -

Soil warming cable  -  Early propagation requires a consistent soil temperature of 12ºC to 16ºC. Germination and root development are very slow below these temperature levels. If you have a large area to heat up then a soil warming cable is ideal. The cables are ready to use and can be plugged into a thermostat for complete temperature control.

Heating mat  -  Like an electric blanket for your seed trays!  It comes with a soil sensor and thermostat, and you can set the temperature up to 40 degrees C. Heating mats can be set up and put away very quickly and can be used anywhere with light and power.

Heated Propagator  -  There are two types available, both need a power source.

Those designed to provide constant, gentle heat.  The electrical element (between 10W and 15W) will increase the ambient compost temperature by about 8°C. There is no thermostat. This type of propagator is usually cheaper and designed to fit on a windowsill. Indoor use only.

Those controlled by a thermostat which can reach high temperatures.  They have a greater wattage - about 85W. Suitable for indoor or outdoor use.  They are easy to take apart and store when not in use.

Hot Press  -  If you get all the towels out of the way this is a great place for starting off your seeds.  Cover pots with a plastic bag so the soil doesn’t dry out.  Good idea to put a sheet of newspaper down first  - otherwise you will have soil everywhere!


Most plants won't grow when they receive less than 10 hours of daylight, winter greenhouse production requires supplemental lighting. Lights can be turned on shortly before sunset to extend the length of the day.


Quality compost is essential.  It should be free of weed seeds and easily wettable and free draining. We stock Klasmann Organic Composts which will give you consistent, reliable results.

General guidelines for best results

  • Make sure soil is firm when sowing your seeds. If sowing in compost then level the compost firmly before sowing.  Outside do not sow in freshly dug soil – it is best to let soil settle first.  The aim is to get your seeds in contact with the growing media, not fall into some black hole of no return.
  • Don’t overdo the sprinkling of seed or you will have to do a lot of thinning.
    The joy of seeds
  • Don’t sow seeds to deep – this is especially true of small seeds.
  • Remember to label your seeds – a lot of babies look the same.
  • Keep records of sowing dates.
  • Don't forget to water!


A lot of vegetables are biennials; that is they grow in the first year and flower and set seed in the second. Examples include most brassicas, celery, beetroot, onions, leeks, carrots and parsnips. Sometimes if they are planted or sown too early they can get a cold check and start to flower in year one – this is known as bolting.

Damping off

Damping off is caused by soil-borne fungi which infect seedlings and causes them to either collapse and decay or to not emerge at all.  It is worse when you have a high level of humidity and poor air circulation.  Damping off is especially damaging in spring when light levels and temperatures are low and seedlings grow slowly.

Control measures -

Always use good quality compost, make sure your pots are clean and free of old compost; sow seeds thinly to avoid crowding and use clean water.  If using rainwater make sure the butts are kept clean and free from debris. Do not overwater and keep seedlings well ventilated.

Propagation Equipment

We have a large selection of seeds, seed trays, tools, seeders and other helpful equipment on our web site.  Please check out the seeds and propagation sction on our website. 

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