Garden tips: How to choose the right compost

There are basically two types of compost, soilless and soil-based.
Hannah Stephenson

AS SPRING approaches, we'll be sowing, planting, mulching and digging – but which compost do we need for each job?

There are basically two types of compost: Soilless and soil-based. Soilless 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.

Soil-based types are better for planting trees or growing permanent specimens in containers, such as shrubs or perennials, and are sold under the John Innes formula. Each John Innes number from No 1 to No 3 contains progressively more feed.

:: Multi-purpose compost

This is the most versatile compost, which can be used to dig in and enrich beds and borders, as well as plant up containers. Many 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

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.

:: 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.

If you love azaleas but don't have acid soil, consider planting them in pots using ericaceous compost.

:: 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.

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

Compost left over from mushroom farming, this is generally cheaper than other composts and is often used as a soil conditioner or to mulch a bed. 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.

The RHS advises gardeners to use it in moderation, alternating with well-rotted manure or garden compost. It's also not suitable for fruit crops.

:: 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 plamts. 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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