An ideal seed compost is able to retain water, whilst at the same time letting excess water drain away to provide an environment that is damp but not waterlogged. It allows penetration of plant roots and is able to anchor plants, but has space for air. Its texture is consistent, and it is free from pests, diseases and weeds that would compete with the seedlings. As we have seen, it doesn’t need to contain many nutrients if seedlings are going to be pricked out; seedlings growing in modules will either need enough nutrients in the compost to support them through their first weeks of life, or suitable supplementary feeding.
Buying peat-free seed compost
It’s important to note that (certainly here in the UK, and I suspect in most places) if a compost doesn’t say it is peat-free then it won’t be. It’s possible that a compost bag may say 30% peat-free or something like that – which means it’s 70% peat! And John Innes composts (which are standard mixes, rather than a brand name) are all peat-based.
Commercially available peat-free composts are still under development, and many brands leave a lot to be desired. Finding a product that works for you is, unfortunately, a matter of trial-and-error and the consistency of peat-based products (which have been on sale for much longer) is one factor that draws gardeners to them.
Peat-free composts are often based on composted waste products, and if they include green waste that has been collected from gardeners then they can be contaminated with bits of plastic and other odds and ends, which some find off-putting but are easily removed with a garden sieve. That they are making use of waste products is an environmental plus, but unless these have been properly composted then their continued decomposition can cause nutrient deficiencies, although this would affect ongoing seedling growth rather than seed germination.
My personal choice (bear in mind I am based in the UK) is New Horizon multipurpose compost, which is made from recycled materials. It does contain larger pieces, which I tend to pick out with my fingers, but if you want a fine seed compost then you can sieve it before use. They do also make a specialized ‘seed and cutting’ version, although I haven’t tried it. I have used New Horizon for several years and have had no problems with it for seeds or growing plants in containers.
Some of the big-store DIY chains produce their own brands of peat-free composts and unfortunately these can be very variable. The UK consumer association Which? regularly runs tests on potting composts of all descriptions, and their results are well worth looking out for. Whenever they run tests on peat-free composts the results are generally well-publicized in the media (albeit with various biases), and over the years the results are generally improving. In 2010 Which? awarded a ‘best buy’ status to three peat-free composts (including New Horizon multipurpose and two products from Vital Earth). The results are always hotly debated by the companies whose products have been maligned.
It’s always worth asking for recommendations from gardeners or organizations you trust – perhaps your local organic gardening association, or the relevant University Extension if you’re in the US.
Whenever you’re buying compost there are some points to bear in mind. You want fresh compost – it doesn’t store indefinitely. Look for bags that aren’t faded or torn, and (preferably) have been stored indoors if there isn’t a big stock turnover. Your chosen compost should emerge from the bag with a nice earthy smell and not be too pungent or reek of decay. Anything with a very lumpy texture is not suitable for sowing seeds, and should be considered a potting compost.
There will be differences in availability (and very possibly consistency) nationwide, although the major players are getting better. And peat-free mixes, especially good ones, do tend to be slightly more expensive than peat-based brands. You do get what you pay for, and it’s worth reducing your dependence on bought compost so that you can make the most efficient use of what you do buy.
Once you’ve bought your compost, store it well before use. It should not be allowed to get wet, which will wash away nutrients. Keeping it covered over also prevents weed seeds, pests and diseases from moving in.
Coir is available compressed into blocks or bricks. These are rehydrated and broken up, and the resulting growing medium (it hardly qualifies as ‘compost’) can be used as is for seed sowing, as it contains very low levels of nutrients. It’s also possible to buy suitable nutrients (including organic choices) to add to the blocks as you soak them, to avoid the need for supplementary feeding of seedlings.
A recent tour of local garden centres proved it can be quite difficult to buy coir blocks outside of the spring sowing season, but they are readily available via mail order and can be a very cost-effective way of raising seeds. The most important thing is to keep the moisture levels even, so the coir is damp but not waterlogged and isn’t allowed to dry out.
Homemade seed compost
Unless you have a very small garden then you may also have the resources to make your own seed compost. If you rake up fallen leaves every autumn and allow them to rot down into leaf mould (over two or three years) then you have a valuable raw material – leaf mould is low in nutrients and makes an ideal seed compost. If you mix your fallen leaves with comfrey to make your leaf mould then you’ll get something similar with more nutrients.
If you don’t make enough leaf mould to fulfill your needs (and it can be difficult in urban areas with few trees) then you can mix it with other materials. Your chosen mix may depend on what you have, but it’s worth making small batches and keeping a record of both the mixture and the results – so you can develop your own perfect mix.
Before it was possible to buy potting composts it was normal for head gardeners to mix their own blends, and to keep the recipes secret – it was their equivalent of proprietary information. I suspect many gardeners still do the same, but some do share their mixes. Monty Don did so very recently in the Telegraph, to support the current anti-peat movement. Garden Organic’s I Don’t Dig Peat campaign has downloadable factsheets including their chosen peat-free recipes.
Other ingredients you may see mentioned include loam, perlite and vermiculite, garden compost, vermicompost (or worm compost), lime, sand and rice hulls. I’m going to explain more about those in the ‘Peat-Free Pantry’ section at the back of the book.
This concludes Chapter 1, which was all about peat-free seed sowing. There will be more information on compost and potting mixes throughout the book. For now, we’re moving onto Chapter 2 – Caring for Seedlings.