There are many, many different types of compost. And it’s not always clear which is the best compost to use for your particular job or task. The compost area in garden centres are often made up of bags and bags that don’t really explain what they are best used for.
To help you work out what the best compost is for potting, we’ve laid out a simple guide to individual composts from ericaceous, to multi-purpose. You should be able to find the best type of compost for your pots. If you’re looking for peat free compost, we’ve flagged up the types for you and don’t forget compost additions, such as fertiliser too.
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• Multi-purpose compost
Pretty much what it says on the tin. Suitable for use in all garden situations and at all stages of growth.
• Seed compost
A potting mix much lower in nutrients than other soil types so as not to overwhelm seeds, and often mixed with sand to create a finer texture to give seeds
the best chance of germination.
• John Innes compost range
A range of compost formulas celebrated for their soil-based content. John Innes mixes are widely used in both professional and home gardens. Some still contain peat (see below), while others use peat alternatives. Check before buying.
• John Innes No.1
Use to pot up young seedlings to allow them to establish before being planted out in their final growing position.
• John Innes No.2
With a rich nutrient content to feed plants for longer, this formula also helps stabilise plants grown in containers.
• John Innes No.3
The richest of the three. Suitable for the final repotting of mature plants that are destined to remain in their pot for a number of years.
• Ericaceous compost
Developed to promote the health of plants needing acid soil conditions, such as rhododendrons, azaleas, camellias and blueberries.
What about peat and peat alternative compost?
Thanks to its capacity to hold water and nutrients, peat has been used extensively for gardening over the past 50 years. But the environmental impact of extracting peat is a concern and more gardeners are increasingly turning to peat-free alternatives, which perform just as well. However, peat-free and reduced-peat mixes vary in consistency. Read the packaging carefully to make sure it is the right product for your plants. It may be necessary to add a specific fertiliser alongside the compost to achieve a suitable growing medium.
Can you use old compost?
Bags of unused or old compost will start to break down and may not perform as well as they would when fresh. Add it to the compost bin, along with other clippings and mix well with plenty of harder material such as straw or cardboard.
Soil fertiliser and other compost additions
It is often necessary to add to compost to improve drainage, water retention or nutrients when planting in containers, as essential elements are much more limited in pots than in the soil. Here is a list of some of the most commonly used additions.
• Horticultural grit
Available in different sizes depending on the desired use. Mix small aggregates into compost to improve aeration and drainage or top dress containers with a more decorative type to mask the appearance of bare soil.
• Leaf mould
A soil conditioner made using fallen autumn leaves collected from the garden. Takes around two years to break down, but once well rotted, leaf mould can be mixed with soil to use as a potting compost.
• Blood, fish and bone
Worked into the soil throughout the growing season, blood, fish and bone provides a natural source of three major nutrients – nitrogen, phosphorus and potassium – to encourage healthy plant growth.
A form of charcoal made with untreated woody waste that remains stable in the soil and helps improve soil structure and water retention, and enhance beneficial microbial activity.
• Liquid seaweed
Rich in micro-nutrients and a sustainable resource. Natural alternative to synthetic or animal-based fertilisers for encouraging healthy production of flowers and fruit. Apply during flowering season.
• Slow-release fertiliser
Concentrated source of plant nutrients, which have no or little effect on soil structure or fertility but will help to combat plant deficiencies. These fertilisers degrade slowly and are dependent on soil temperature.
Pebble-like in appearance, hydroleca has the capability to absorb a large amount of water and then release it slowly to keep plants hydrated. Use as a pot topping, or
in place of crocks for drainage.
Carbon Gold 0117 244 0032, carbongold.com
Clover 028 8774 0488, cloverpeat.co.uk
Dalefoot Composts 01931 713281, dalefootcomposts.co.uk
Levington lovethegarden.com Melcourt 01666 502711, melcourt.co.uk
Thompson & Morgan 0844 573 1818, thompson-morgan.com
Westland 01480 443789, gardenhealth.com