What compost to use

What Compost to Use

The medium – usually some sort of compost – that you use to sow your seeds in is important to make sure you're getting your seeds off to the best start. Here are a few things to bear in mind when choosing.

The most important point is to use peat-free compost.

• Peat is not a renewable resource and comes from peat bogs, which have been irreversibly depleted by harvesting for horticultural use.
• Peat bogs are fantastic for storing huge amounts of carbon, so by depleting them we are contributing to climate change.
• They are also unique ecosystems that support diverse communities of plants and animals.

The UK is phasing out peat from horticulture and within a few years we will no longer be able to buy compost containing peat, but we can all help by choosing peat-free compost now.

Just check the compost bag for a 'peat-free' label when you buy.

Finding the Right Compost for You

Horticulture has relied on peat for a long time, so now we are in the process of lots of different peat-free composts are being developed. Some are better than others.

• I find coir-based peat-free composts can be too fibrous for seeds, and as we saw earlier, coir isn't the most sustainable choice.
• Some peat-free composts can dry out quickly on the surface. For seeds, it's worth finding one that you feel has good water retention.
• Water little and often, and remember that with peat-free, even if the top looks dry, it will often still be moist lower down (check by poking a finger into the compost or lifting the pot). For established plants a dryer top is fine, but for seeds, it's worth just ensuring the top stays moist.
• Every manufacturer and blend is different, so it's worth experimenting to find the best mix for you. Don't lose heart if you've had disappointing results with a mix – simply try another.

I use a bark-based compost called SylvaGrow by Melcourt, just their multipurpose compost. It has a few larger pieces in but you can sieve or pick these out before using it for seeds.

Different compost mixes are tailored to the needs of different types of plants. For example, seed compost has the right nutrients for seeds.

• I use multipurpose SylvaGrow, which though not labelled as a seed compost, includes growing from seed as one of its purposes. I sift through to take out the large particles or sieve it.
• If you are sowing a lot of seeds it may be worth using a dedicated seed compost, such as SylvaGrow seed. However, bear in mind that bagged compost starts to deteriorate after a few months, so you'd want to either use it up within the season or share a bag with a friend.

Compost Versus 'Compost'

The term 'compost' can be confusing because it is used for the homemade organic matter we make in our gardens from recycling our garden waste, but also the pre-made potting mixes we buy in bags from the garden centre, which are technically called growing media.

• It is possible to use homemade compost for sowing seeds and potting in, but it's not a sterile medium and might not have the right nutrient levels or optimum texture for seeds, so results would be mixed.
• The bagged 'compost' (growing media) that you buy is very different – it has been carefully developed to provide an optimum growing environment and will have the right nutrient balance for young seedlings.

Top Dressing

A top dressing can be useful for sowing. There are two main options that are good for seeds.

1. Vermiculite – a very light volcanic mineral that is popular. However, vermiculite is not very environmentally friendly as it is mined, processed at very high temperatures and then imported over long distances if you're in the UK.

1. Milled cork – a good and widely available alternative, which has a similar light texture and is more sustainable. It's the bark of the cork oak, which regrows after harvesting and comes from Europe.

These are both used in the same way: scatter on top of the seed tray for any seeds that need light to germinate, to provide a moisture-retentive sterile layer for germination while still allowing light in.

Potting Tray

This is another piece of equipment that's really useful when handling compost. Mine is made of wood, as this looks nicer and is more environmentally friendly.

• This sits on the greenhouse bench and helps to keep things tidy.
• I put the compost into it and fill the pots in it. This saves me bending to pot over the bag.

Further Reading

Free RHS web advice and resources on peat-free growing:

• RHS: Using peat-free compost for seeds and cuttings
• RHS: Choosing a peat-free compost
• RHS: Everything you need to know about peat, peatlands and peat-free