Guide to Growing Edible Plants From Seed

Life gets busy sometimes, and that's when seedlings are the answer for a quick and convenient edible garden.  But growing plants from seed can be incredibly rewarding, and is a super money-saver.  This guide to growing edible plants from seeds takes you through the basics of seed raising. 

The golden rules for growing plants from seed

Growing plants from seed isn't as complicated as people make out.  There are 5 basic seed raising rules to follow:

1. Plant you seeds in a good quality seed raising mix

Don't think that any old dirt will do!  Seeds need a light and nutritious soil mix to germinate.  Buy something fit for purpose! 

2. Plant your seeds at the right time and at the right temperature 

Take note of the recommended planting season on the seed packet.  Many summer edibles (like chillies, capsicum and aubergine) won't germinate until the nights are warm and the soil has heated up. You can simulate these conditions by keeping your seedlings in a greenhouse until it is warm enough to plant them outside.  

Similarly, some seeds need to be exposed to cold and moisture before sowing to 'break dormancy' and begin the germination process.  (This is called 'stratification'.) In nature, stratification happens when a seed is planted in autumn and experiences the winter chill before germinating in spring.  This process can be artificially simulated by potting up the seed, sealing it in a bag and refrigerating.  The length of time you refrigerate the seed depends on the variety.

3. Don't sow your seeds too deeply

If you plant your seeds to deeply, they won't germinate.  The size of the seed is an indicator of how deeply to bury it.  Generally you sprinkle very fine seed on the surface, and press it down. (Indeed some seeds (like Poppy seeds) need light to germinate, so they won't sprout if you bury them under a layer of soil.  Larger seeds should be sown no deeper than twice their diameter.  

4. Keep your soil evenly moist but not soggy

Seeds need moisture to germinate, but not too much.  Spray your seedlings with a mist of water every day to keep the soil moist but not soggy.

5. Let your germinating seeds see the light!

How many seeds should I plant?

Not all seeds successfully germinate.  While you should just sow one large seed per hole, with smaller seeds you can plant two-three seeds per hole.  This increases your chances of germination success.  When your seeds germinate, keep the strongest specimen and snip the others off at the soil line.  (This reduces competition for root space and nutrients.)  Some seeds, are difficult to sow neatly, so I like to broadcast them evenly and then thin them when the seedlings and baby carrots come through.   

Should I presoak my seeds before sowing?

Not all seeds need to be presoaked.  However, larger seeds with a tough outer shell often do better if you presoak them.  These seeds often come from colder climates where their outer shell protects them from the cold.  Presoaking helps the plant embryo to break through the outer shell.  If in doubt, follow the instructions on your seed packet.

Should I pinch out the tips of my seedlings?

Not all seedlings need to pinched at the tip, but if you would like a herb or flower seedling to bush out, rather than grow up, then it is a good idea.  Basil, Cosmos, Marigolds and Snap Dragons usually do better if you pinch out the tip, for example.

Wait until your baby seedling has developed several sets of true leaves, then use your fingertips to snip off the stem at the top of the plant.  Pinch the stem just above the point where the leaves connect to it. 

Wait until the seedling has developed several sets of true leaves (don't count the cotyledons, or seed leaves, that appeared when it first sprouted).  This encourages the plant to bush out and develop more leaves.  

Should I direct sow or transplant my seeds?

Many seeds can be direct sown into the garden if the temperature is right - check your seed packet for instructions.  Some seeds, like carrots, are best direct sown, as they don't like their roots to be disturbed.

The seed packet will also tell you if it is better off to start your plants inside when you can transplant them into the garden.

Why haven't my seeds germinated?

If you have tried raising seeds before without success, there are a few possible reasons:

  • The wrong type of soil (too heavy or not nutritious enough)
  • Sown too deeply
  • Wrong soil temperature (too hot or too cold)
  • Too much water
  • Fungal disease (called 'damping off')
  • Slugs and snails have got to them

How should I store my seeds?

Store your seeds in an airtight container in a cool (not cold), dark and dry place.  This extends their shelf life.