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Make your own seed compost

Many seeds need special seed compost. Well they would, wouldn't they? Not any old compost or soil for your seeds - particularly if you want to give them the best possible chance of germination and growing From Plot to Plate.

But why is that?

Well let's first think about what germination actually means. It's simply the process by which a previously dormant seed starts to grow and develop into the seedling that will eventually become a plant. Simple enough but often over looked or taken for granted.

So what does the seed actually need to germinate? Well there are 4 main elements:

  1. water

  2. air

  3. temperature &

  4. light

If the balance isn't right then chances are our seeds will fail to germinate and we'll end up back at square one.

One of the best ways we can get our seeds to germinate is by giving them a good start. In most cases that means we need to think about what we sow them in. Let's look at how that simple thing might not be as simple as we might otherwise have thought.

That initial growing medium needs to be able to support the seed in it's infancy. To do that it doesn't need much in the way of nutrients - ordinary garden compost when used on its own is usually too rich for our seeds. The growing medium also needs to have the right texture and drainage for seedlings to germinate and grow - so as to give them the best possible chance of balancing that air and water requirement.

But what can we used? Well this is one of the four ingredients we're trying this year:

It's free and it's nice and fine. It's the soil from mole hills - not something that many of us would have given much attention to before. Apart from moaning about those moles digging up our gardens. The soil is good - and far better than anything we could dig up and sieve as it is so fine. This is great for those seeds as their roots start to develop.

Some people might want to sterilise the soil before they use it - that would simply mean putting it on a metal tray and popping it in your oven for a bit. Doing so would kill off any seeds - weeds - that might have found their way into the soil. We tend not to do that and simply keep an eye out for anything unusual that might pop out of the mix during the germination process. If anything does, we simply pull it out!

The next thing we're going to add is some coir - pronounced coy-er. Ok so we had to buy this is as it's not the sort of thing that many of us will be able to find naturally. Why's that? Well that's because it comes from a coconut! It's the natural fibrous coat of the coconut and I doubt many of us are growing those in Somerset! It can be bought loose or in blocks or in discs and it's a useful addition to any peat free soil conditioner. We'll talk about general soil conditioners another time but for now this is what it looks like.

We also add some of our own leaf mould if we have any that's ready. That also helps with drainage and improves the structure of our seed compost. Again we'll talk about leaf mould another time but here's some we had breaking down at the allotment. You can see that there are some twigs in amongst those leaves and we'll sieve them out before we add them to our mix. We'll add the larger material and twigs back to the compost heap - nothing goes to waste. Where the leaves are too big we'll chop them up a bit and crumble it all together.

We would have liked more leaf mould but sadly the rest of those leaves we had gathered up hadn't quite decomposed enough. We have to make do with whatever we have - it is nature after all. The other thing we could have done was look for decomposed leaves around the garden and allotment. If you've not tidied up some of your plants and left the leaves to decompose where they fell then you might find some there that you could use - hellebores are often a good source.

Leaf mould - like coir - is effectively the peat that many of us might have used in the past. It's main purpose in the mix is to add bulk to the compost and help with water retention for our seeds. If we don't have enough leaf compost then we'd simply add some more coir - or vice versa.

The final thing we add is vermiculite. And again this is something that we need to buy as it's not something that is naturally found in Somerset as it's a mineral that is mined and then undergoes a heat treatment process that means it expands into small pieces. This is what it looks like.

It doesn't deteriorate or rot, its mould-resistant, has no smell, enjoys insulation properties and is neutral on the ph scale. This means that this lightweight material is an ideal addition to our seed compost as it gives some structure to the growing medium that allows 3 of those 4 main requirements - water, air and temperature - to reach our seeds and help with germination.

So what next?

Well we get our trusty and rusty old wheel barrow out and start mixing. Thoroughly. With our hands.

And it's easy. You don't need to worry too much about exact amounts. It's simply 2 parts of sieved mole hill to two parts coir or leaf mould to one part of vermiculite. We tend to use an old (but clean) flower pot as our measuring guide.

  1. We sieve 2 pots of mole hill soil - just to remove any stones or weeds that we might have scooped up. We don't sterilise it in the oven, although that can be done.

  2. Then we add 1/2 pot of sieved leaf compost.

  3. Then 1 and 1/2 pots of coir.

  4. Then 1 pot of vermiculite.

When it's all mixed together it looks like this. Wouldn't you like to spend your initial few formative days stood in amongst all of that?!

And that's it. All you need to do now is keep it somewhere dry and look forward to using it. Or better still, start that germination process off as soon as you can. We'll be using ours for our sweet peas and broad beans over the next few days - and we'll be sure to post updates about how we do that and how we get on!

Comments or questions? We'd love to hear from you! Get in touch in through our facebook page or email us at


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