No time or room to make your own compost, and want to know how to use compost effectively? Here’s our guide for how choose from the different types of compost for your garden, and where best to use it.

How to use compost guide

As spring approaches, we’ll be sowing, planting, mulching and digging – but which compost do we need for each job? To keep things simple, be aware that there are basically two types: Soilless and soil-based.

Soilless

These types are ideal for quick-growing crops or annuals in pots, where the plants are only going to be in the pot or container for a year. These are mainly made up of organic matter such as bark, coir, green waste, paper, leafmould and sawdust, with added nutrients and water-retaining agents.

Soil-based

These are better for planting trees or growing permanent specimens in containers, such as shrubs or perennials. They are sold under the John Innes formula and are made from a mixture of loam, sand or grit and peat, with plant foods added.

Each John Innes number contains progressively more feed:

  • John Innes No. 1 – good for pricking out or potting up young seedlings
  • John Innes No. 2 – has more nutrients and is used when potting up small plants and vegetable plants in containers
  • John Innes No. 3 – ideal for mature plants, permanent plantings in pots and when planting trees and shrubs.

Here’s what you need to know about the different types of compost available…

Multi-purpose compost

Multi-purpose compost
Multi-purpose compost

This is the most versatile type, which can be used to dig in and enrich beds and borders, as well as plant up containers. There are many which contain blends of ingredients, including plant foods which can feed your plants throughout the season, water-retaining properties and added John Innes.

Peat-free compost

Many gardeners are opposed to composts containing peat because they continue to deplete British peat bogs, although historically, peat has been used because it’s good at holding water and retaining nutrients.

(Westland/PA)
(Westland/PA)

Some gardeners argue that plants grow better in peat-based products, but others insist that if you adapt to the properties of peat-free, you should be fine.

Peat-free composts generally retain water better, which is great in hot summers, but can lead to rotting plants in wet winters. So add grit to your peat-free compost before planting to enhance drainage and water your plants little and often during the summer, rather than completely soaking them once a day.

Check the wording on the bag – if it doesn’t say ‘peat-free’ then it generally isn’t. Marketeers may use wording such as ‘environmentally friendly’ and ‘organic’, but that doesn’t necessarily mean it’s peat-free.

Recommended: Peat-free compost guide – make your garden peat-free in 2020

Ericaceous compost

Acid-loving plants including camellia, azalea, rhododendron and heather are best planted using ericaceous compost. If you are planting them in a flower bed that naturally has alkaline soil, they are likely to suffer, as sooner or later the ericaceous compost will lose its efficacy and the original soil make-up will seep through.

Ericaceous composts
Ericaceous composts

It’s often better to choose plants that will like your existing soil, rather than trying to adapt unsuitable plants using specific composts. If you love azaleas but don’t have acid soil, consider planting them in pots using ericaceous compost.

Heathers also do well in ericaceous compost (Thinkstock/PA)
Heathers also do well in ericaceous compost (Thinkstock/PA)

Seed and potting compost

Seed compost has the lowest amount of nutrients, which encourages the best germination and growth of tiny roots. A seed compost is much more in tune with the needs of a developing seed than a general multi-purpose compost.

How to use compost when potting or bringing on seeds.
How to use compost when potting or bringing on seeds.

Low nutrient levels don’t affect the plant growth because individual seeds already contain a store of food to feed the developing plants.

Spent mushroom compost

This is generally cheaper than other composts and is often used as a soil conditioner or to mulch a bed. It is called ‘spent’ because it is left over from mushroom farming.

It has a high lime content so is ideal for the vegetable garden as veg crops, including brassicas, grow best when the soil is not acid. However, don’t place it near acid-loving plants like azaleas and rhododendron.

Spent mushroom compost is good to use as a mulch (Thinkstock/PA)
Spent mushroom compost is good to use as a mulch (Thinkstock/PA)

The RHS advises gardeners to use it in moderation, alternating with well-rotted manure or garden compost, which should help balance the alkaline nature of mushroom compost. It’s also not suitable for fruit crops, which need a more neutral or acid soil.

Animal manure

Animal manure is a fantastic soil conditioner, but it must be well rotted before adding to the soil, or the concentration of nitrogen will scorch young plants.

Horse manure needs to be given time to rot down before use (Thinkstock/PA)
Horse manure needs to be given time to rot down before use (Thinkstock/PA)

If you are offered fresh manure, you’ll need to create a space to rot it down for at least six months before spreading it across the soil in spring, a few weeks before planting. Break up any lumps by raking it and mix in some topsoil.

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