With most gardeners using compost to sow seeds, top-dress pots and transplant seedlings, knowing which medium to use can be problematic. Then there’s the peat issue. If the compost isn’t labelled as being peat-free, it won’t be.
For most plants, and for many seeds and cuttings, a good peat-free multi-purpose compost is suitable, both from an environmental and convenience point of view.
Multi-purpose composts are soil-less, so they shrink more than loam-based composts when they dry out, and don’t always reabsorb water when wetted. It’s therefore important to keep the compost gently moist at all times and don’t let it dry out.
The nutrients are also more rapidly leached out of soil-less composts than those containing loam. Read the bag for how long the nutrients are expected to last, but you will usually need to start applying a fortnightly liquid feed six weeks after planting plants that are in growth. For trees and shrubs in containers outdoors, use John Innes soil-based compost, which has the weight necessary for stability and the ability to hold onto its nutrients for longer – add grit to prevent it from becoming too hard and ‘claggy’.
If you’re determined to avoid peat, the alternative is to mix a peat-free, multi-purpose compost with good-quality topsoil, to provide stability and moisture retention, and add fertiliser, such as blood, fish and bonemeal. Proprietary compost is tested to make sure it’s suitable for a range of plants. Yours will be a process of trial and error, but you will have the satisfaction of knowing you’re doing your bit for conservation.
For acid-loving plants, such as rhododendrons and camellias, use John Innes ericaceous compost or mix a peat-free ericaceous compost with neutral or acidic topsoil.
Whatever compost you choose, for best results always buy fresh bagged compost rather than an old, stale or waterlogged sackful. Only buy as much as you can use within six to eight weeks, and seal after use to stop bugs and weed seeds getting in, and prevent decomposition. Store it where it won’t get waterlogged.
Find out which compost is best for which job, below.
Sowing most seeds
Preparing seed tray for sowing seed
Use peat-free, multi-purpose compost.
Potting on plug plants
Use peat-free, multi-purpose compost.
Use peat-free, multi-purpose compost with half as much vermiculite or perlite added.
Plants in pots for less than a year
Potting up a hanging basket
These include hanging baskets, summer bedding and veg. Use peat-free, multi-purpose compost.
Plants in pots for more than a year
Use equal parts of peat-free, multi-purpose compost and John Innes No.3, or a good topsoil if you want to avoid peat.
Large plants in large pots kept outdoors for several years
These include shrubs and fruit. Use John Innes No.3 with one quarter its bulk of added grit, or a good topsoil if you want to avoid peat.
These include rhododendrons and camellias in large pots. Use John Innes Ericaceous Compost or a peat-free ericaceous compost.
Cacti and succulents in pots
Use John Innes No.1 with grit added until it feels crunchy, or a bespoke cacti compost.
Repotting an orchid
The epiphytic types (those that cling to trees for support) are best potted into chipped bark especially for the purpose.
Use peat-free, multi-purpose compost (except for cacti, other succulents and orchids).
Adding to planting holes
Use well-rotted garden compost or manure, but many gardeners now recommend simply enriching the soil in the area where you will dig the hole.
Adding a mulch around roses
Use well-rotted garden compost or manure, or composted or chipped bark (the latter is longest lasting).
Use good-quality screened (sieved) topsoil.
Filling raised beds
Use screened topsoil with well-rotted garden compost or manure added.