Why sow seeds indoors?

We have seen that seeds want to germinate, and we know that they do so successfully in nature – otherwise plants would be few and far between. It’s perfectly possible to sow seeds outside, into the soil, and we’ll be looking at soil improvement and preparation later on in the book. So why do so many gardeners choose to sow their seeds in pots and trays indoors?

The natural environment can be a dangerous place for a seed. Even if it lands in a suitable place and conditions are right for it to germinate, there are other perils ahead. Birds and rodents eat seeds, and there are diseases that attack seeds and young plants and kill them before they get growing. Although conditions might be right for germination, they may not continue to be suitable for growing – drought may follow rainfall, sudden frosts could occur in late spring, or ground may become waterlogged.

Gardeners can avoid many of these problems by taking control of the seed sowing environment, but it does come at a price – the seeds become utterly dependent on you to give them what they need until such time as you put them outside in the garden.

Sowing seeds indoors gives you control over water and temperature, allowing you to sow seeds that wouldn’t normally grow in your climate, or to get a head-start with marginal plants that need a longer season to mature than you have. You can sow them indoors when the weather outside is too cold for them to survive.

Indoor sowings into a suitable sterile medium are free from pests and diseases, and using clean water and clean containers helps to keep them that way. You also avoid competition with weeds that can grow quickly and swamp young seedlings.

All of these factors mean that, done properly, seed germination is likely to be more successful and reliable indoors than out. You’ll need less seed to achieve the same result, which is helpful with seeds that are expensive or rare.

And sowing indoors can help you make better use of a small space outside, with seedlings ready to plant out whenever a space is freed up. That’s particularly useful in the vegetable garden where successional sowing means that you can have regular batches of seedlings ready for when you clear away a previous crop, although it’s perfectly possible to have a seed bed outside if you have the space.

Pomegranate seeds

Seed Sowing Basics

Basic seed sowing technique is very simple.

  1. Choose your container. You can use proper seed trays, recycled food containers, modules or biodegradable pots, but the idea is the same – you want a container that holds a suitable volume of compost or soil and will hold water but also allow excess water to drain away.
  2. Add a layer of peat-free seed compost*. How deep the layer needs to be depends on the size of your seeds – small seeds won’t need much depth, but peas and beans need a bit more. Don’t overfill the container, as you need to be able to add some water.
  3. Give the container a bit of a shake to even out the compost, and then gently press the surface down with your hand or something flat (you can buy special tampers to do the job). What you’re aiming for is a compost structure that is loose enough for roots to grow into, with spaces for air and water but no big voids where roots can’t go – think chocolate mousse rather than Swiss cheese.
  4. Water the compost, so that it’s damp but not waterlogged. The traditional way to do this with seed trays (which have drainage holes in the bottom) is to stand them in the sink for 30 minutes or more while they soak up water. They are then left to drain for another 30 minutes or so to ensure they’re not water-logged. My personal method is to use a plastic bottle with a small rose on the top (a bottle-top waterer) that allows me to squirt on water as I want to. You water before you sow the seeds so that the water doesn’t move the seeds around or cause big mounds and dips in the compost.
  5. Sow your seeds onto the damp compost. There should be a recommended spacing on the packet, but sowing seeds thinly (i.e. fewer of them) is generally best as it gives each seed some room to grow and avoids the problems of overcrowding. You should also avoid sowing far more seed than you need plants – when it comes time to prick them out, pot them on or plant them out then you’ll either be making extra work for yourself or throwing good seedlings on the compost heap.
  6. The depth seeds are sown at is also important. Again, there should be some clues on the seed packet, but smaller seeds are sown at quite a shallow depth because they don’t have enough energy to grow up through a large amount of compost. It’s helpful to sow them on the surface of the compost, then sprinkle a thin layer of compost or vermiculite over the top (unless you know they need light to germinate, in which case leave them uncovered).
  7. Larger seeds like peas and beans are sown deeper (I poke mine in with my finger), but generally no further down than twice the size of the seed. Again, you can top off the container with a layer of compost to level it out and cover the seeds over.
    Seed germination is best when there is a reliable level of moisture, so sown seed trays are usually encased in a plastic bag, put into a propagator or simply given a lid that helps to stop all the water evaporating. In this case you shouldn’t need to water before the seeds germinate; if you leave your compost uncovered you may need to water to keep it moist, but use a mister or a fine rose that doesn’t disturb the compost.
  8. Leave your seed trays somewhere that has the right temperature range for your seeds. If they are too cold they won’t germinate; most need heat and not light so the airing cupboard is a popular location. Windowsills are also good, but be careful that they don’t get too hot and that you keep the compost moist.
    Check daily to see if your seeds have germinated. Once they do then you have seedlings to look after.

*Now that everyone is up to speed on seed-sowing, I will move on to the specifics of peat-free seed sowing – choosing a suitable seed compost or making your own, and choosing suitable containers to avoid the need for pre-formed peat pots and pellets. Feel free to leave comments, your hints and tips or topics you’d like to see covered.


This blog post was written by Emma Cooper and was published on The Unconventional Gardener website. If you're reading it elsewhere you may want to navigate away from plagiarised content.

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