Posted by Sue
Five Top tips for Successful Seed Sowing Indoors

How to Germinate : 5 Easy Steps To Successful Indoor Seed Sowing

Before you open that packet of seeds, take a moment to think about how plants grow and what they’ll need to thrive.

A seed is a dormant plant; it’s alive and waiting to start growing as soon as the conditions are right. That’s why there’s a date on the packet telling you when it’s been ‘packed’ or a ‘best before’ date.

So start off with fresh seeds packed in the last one or two years and gather together all the equipment you need to help them germinate.  

1. Sterile compost is essential for sowing seeds

Seedlings are very vulnerable to pests and diseases and need extra protection at this stage of their life. So start them off in a clean, sterile growing medium such as bagged seed sowing compost or use a block of peat-free coir. Homemade compost or soil from your garden will contain microbes and insects that could harm the young plants. It could also have weed seeds, which may grow and compete with your vegetable seeds. When you are preparing the compost break it up with your hands to create a fine texture and remove any lumps.

What compost to use to sow seeds?
Best containers for sowing seeds

2. What are the best containers to use to sow seeds?

Suitable containers are anything that is porous or has drainage holes and can hold compost/coir. Watch out for paper or cardboard-based containers as they may collapse when they are too wet or suck away moisture from the seedlings’ roots when dry. If you don’t want to spend money on purpose-made containers use yoghurt pots, the base of plastic milk bottles, and mushroom or fruit trays (check they have drainage holes in the bottom and clean them thoroughly).

Getting the correct size of container is crucial and it varies for different vegetables. If you put a seed in a container that is too small its growth will be stunted, it could dry out quickly and die. You will move most of these vegetables into bigger pots as they grow, but here’s a quick guide to correct container sizes for when you first sow the seeds:

Suitable for a shallow container 3-5cm deep

Lettuce, Kale, Radish, Cabbage, Spinach, Beetroot, Pepper, Tomato, Aubergine, Onion seeds

3. Now you're ready to sow your seeds!

When you’ve chosen your container fill it lightly with the compost/coir; don’t push it down as you go. Fill the container to the top and then tap if firmly on the table and the compost will sink a little, then firm it down with your hand or another container the same size. You should now have a level surface to sow your seeds into.

Make sure you sow the seeds at the correct depth for that type of vegetable. On the seed packet you will see the correct depth shown in ‘mm’ or ‘cm.’ To sow the seed at the correct depth you can either

  • Create mini trenches in the compost to the correct depth
  • Make holes in the compost to the correct depth
How to successfully sow seeds

Tip some of the seeds from the packet into your less dominant hand and then you can pick them up with your dominant hand and sprinkle one seed into each hole or one per centimetre into the mini trenches for small seedlings. Once you’ve finished, push the compost over the seeds you’ve sown. For large vegetables (beans, squash, courgette) space out the seeds much further, only putting two or three seeds in a large pot with a diameter of 15cm. Peas should be sown 4cm apart.

Make sure you have something to label your seeds with, so you remember what you’ve sown where and always put the date you sow the seeds, so you can check how long they are taking to germinate.

How often to water germinating seeds

4. Watering your germinating seeds

Seeds prefer watering from the bottom; put your containers in a tray or bowl and pour water into the tray so the compost and roots can draw up the water.

Watering in this way makes it harder to overwater your seedlings; if there is still water in the tray you don’t need to add more water. Wait until the tray is dry and then add about 1cm of water and don’t water again until all the water has gone.

If you see green algae forming on top of the compost wait until the compost dries out a little before adding more water.

5. What are the right levels of sunlight and warmth for successfully sowing seeds?

Sowing vegetable seeds indoors in containers will give them that extra boost of warmth to kick start germination. There is more warmth indoors but less light, so find a sunny windowsill in a cool room (remember our ‘cool’ room is still summer temperatures for seeds). As the seedlings grow, keep turning the container around so the seedlings don’t all lean over towards the light.

For help with the next steps see my post on ‘Aftercare for Seedlings’.

How much sunlight for germinating seeds

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