How I Make a Seed Mix
I've come to find that seed mixes vary a huge amount. There seems to be no right or wrong answer unless of course you come up with a concoction that produces no seedlings! Another thing I have found is that it's not worth getting too hung up about either. At the end of the day, seeds need very little to get themselves up and running. Usually just a bit of dampness and a bit of warmth. Indeed, most seeds will germinate to one degree or another just on some wet tissue paper or cotton wool.
What I look for and try to achieve is a low cost, fluffy mix that doesn't bind together in clumps. Perhaps the most important aspect thought is that the mix is free from lumps, stone or anything that hasn't broken down. Bags of 'purpose made' seed compost can set you back a lot of money, and claim to have special formulas with added this that an the other. I believe those sorts of products are just not needed.
So how do I create a seed mix then? Simple. I'll usually make my seed compost in batches of around 20 to 25 litres at a time. I start with a bag of normal multi-purpose compost. This in itself more often or not will do the job, but depending on how good the quality is, you can often find it contains remnants of other green waste. Many garden centres will have an open bag of each compost, so you can get your hands in it. If you have the chance, get a couple of handfuls and run it through the fingers. Pieces of bark or wood not yet rotted down aren't going to be the end of the world, but beware of pieces of plastic, glass or wire. If you come across any of these, it's obviously not checked or goes through any significant quality control. If that is all good, get your nose on it too. A good compost should not smell strong or pungent. It certainly should smell of any chemicals. Sadly over the years, the rush to mass produce peat free compost have seen manufacturers source raw materials from anywhere and everywhere and often there seems to be little regard for screening.
Once I've found a good compost, I'll take around 10 litres of it and run it through a sieve to remove any clumps or bits that cause damage to the delicate roots of newly started seedlings. This is really important because when it comes to potting on, ideally you need to be able to free as much of the root system as possible from the seed tray. Pieces of stone, wood or bark could cause damage.
At the first attempt at turning the gardening world into one of purely peat free compost, the UK went mad for finding alternatives. Some compost providers went out and sourced all sorts of raw materials to try and come up with the perfect blend. But, waiting in the wings, as it had done for some years was coconut coir. Now, there's not a huge amount of nutritional value to coir, but it is entirely natural and is an excellent way of bulking up your seed mix. Volume wise, litre for litre, it is considerably cheaper than purpose made seed compost. Very occasionally, you do come across it for as little as £1.50 a block, although these days, prices have crept up because it's now so popular with gardeners.
Another good thing with coir is that you can buy it in dehydrated blocks. A typical block will rehydrate to around 10 litres in volume.
Some people choose to use pure coir to start their seeds off in. It's a perfectly valid way of doing things. Personally, I prefer to use it as part of a mix though, and combine it with the nutrients provided with a multi purpose compost too.
Coir blocks come in a bag which can be unwrapped and opened up. A block of this size needs around 3 litres of warm water adding to it to rehydrate.
After adding the water, I leave it all soak in the bag for 5 to 10 minutes then massage the bag to break up any remaining lumps. Once I'm happy all the water has been soaked up, the coir is tipped out and I go through it with the fingers to break it up further until it's light and fluffy.
There is one more optional ingredient that I add to my seed mix, and that is 4 or 5 handfuls of vermiculite. It's not essential though. I add it for it's moisture retaining properties and to keep the structure of the mix nice and crumbly. Used in small quantities or in shallow seed trays, your seed mix can dry out quickly, especially in a warm polytunnel or on a heat mat, so the addition of vermiculite just helps retain moisture a little longer.
Now, it's just a question of rolling the sleeves up and mixing it all up. By the end of the process, we have a seed mix of 50% coir and 50% sieved multi purpose compost, with the optional addition of vermiculite. I tend to create the mix and then store it in a container ready for use, should I not need to use the whole batch in one go.
It's probably important to only create a mix as and when you need it, and to avoid it sitting around all year waiting to be used. If it were left to dry out totally, you'd end up with a very fine and dusty mix which could be tricky to moisten back up at a later point without turning it into another clumpy mess. Another reason in my case to only make small batches at a time.
