When it comes to buying compost for a variety of gardening needs, it can be a daunting task to choose which is most appropriate from the wide range of options. All types of compost – even home-made– have their specific uses. To simplify the choice, here’s the lowdown on how to choose the most appropriate type of compost depending on its intended purpose.
John Innes compost:
Let’s start with John Innes, a name we might recognise but perhaps not actually know what makes it so beneficial to plants and why it is more expensive. John Innes was a British 19th century property developer and philanthropist who developed Merton Park in London into one of the country’s first garden suburbs. When he died in 1904, the bulk of his fortune was left to establish the John Innes Horticultural Institution which gained internal recognition as a centre for plant science and genetics.
The three types of John Innes Compost were formulated by researchers at the Institute in the 1930s and are still widely used, nearly 100 years later. Each formula is graded by their nutrient density and, unlike other multi-purpose composts, they all contain soil, making it much heavier with the benefit of helping to stabilise pots at risk from blowing over. It does not dry out quickly – forming a crust like some multi-purpose compost do – or shrink in a pot, so it is easier to water evenly.
No 1 is used for seeds. It has the lowest nutrient mix, designed specifically for seed germination, striking cuttings and growing delicate young seedlings.
No 2 is used for potting as it contains double the nutrients of the seed compost. It is ideal for pricking out and potting on young, growing plants into larger containers.
No 3 is for mature plants as it features the highest concentration of nutrients. It is ideal for planting larger shrubs and mature plants, particularly in heavy tubs.
Seed and cutting compost:
Peat-free seed and cutting compost has been specifically developed with a high phosphate formula plus additional vital minerals to encourage germination and strong root growth, making it ideal for seeds and young plants. The nutrients will feed the seeds and cuttings for up to six weeks. However, some plants are hungry and if any leaves start to go yellow, take it as a sign they need additional feeding with some suitable plant food.
Bulb fibre:
Multi-purpose compost can be used when planting bulbs in pots and containers, but a peat-free bulb fibre has a more open, free-draining texture and this can help prevent over-wintered bulbs from rotting. The soil texture of this specialist compost has additional nutrients which will encourage faster and stronger root growth, leading to healthier bulbs which stand a better chance of flowering again the following year.
Peat-free multi-purpose compost:
Now that the addition of peat has been phased out of compost production, there is a wide variety of standard peat-free multi-purpose, made with a mixture of coir (coconut fibre), composted bark, wood fibre and green compost (similar to home-made garden compost). The mix is lightweight, reasonably free-draining and is ideal for pots, planters and hanging baskets.
You can also buy organic multi-purpose made from certified mixes of organic matter such as composted manure or seaweed. This compost is ideal for organic vegetable and fruit growing.
Moisture-control blends contain water-retaining gels or granules and is the perfect compost for hanging baskets and patio tubs which dry out quickly in warmer weather. Be careful if you use this over the winter, however as with heavy rain, your compost can become too saturated and the plants will rot.
Shrub and Rose compost:
Used both for planting shrubs and roses in the garden and in pots, this formulation of compost has a nutrient-rich content designed to help woody plants establish roots, encouraging growth and blooms. When planting roses in pots, you can mix this two thirds/one third with well-rotted manure to help feed the rose roots.
Ericaceous compost:
If you do not live in an area with naturally occurring acidic soil, you’ll struggle to grow acid soil lovers in your garden. However, plants such as azaleas, rhododendrons and camellias can be grown in pots using ericaceous compost. This is enriched with an iron and zinc complex which is slowly released providing the optimum acidic soil pH. The additional nutrients promote chlorophyll production for greener, glossier foliage and the zinc helps build plant resilience. Plants grown in this type of soil in pots should also be fed with an ericaceous plant food.
Citrus & Mediterranean compost:
With warmer summers more people than ever are planting olive trees and/or growing citrus trees outdoors before over-wintering in more sheltered locations. The formulation for this type of specialist compost has a slightly acidic pH 6-6.5 and has excellent drainage to prevent root rot. It is likely also to include perlite, horticultural grit or sand to ensure air circulation and drainage. Many are loam-based mixtures containing an even mix of sand, silt and clay.
Soil conditioners:
There are a wide variety of soil conditioners and well-rotted farmyard manures available on the market and gardeners who have sufficient space can make their own soil conditioner from composted garden waste. Adding soil conditioner to heavy clay soil, tired garden soil and new gardens to enrich the soil and add texture is key to successful plant growth.
Leaf mould:
Leaf mould enhances soil structure and once fully rotted, is primarily broken down by fungi rather than bacteria, making it a wonderful fine-textured, low-nutrient base for improving soil, starting seeds, or potting young plants. It also acts as a mulch and weed suppressant, and plants such as ferns love it.
Making your own leaf mould in the autumn could not be easier. Rake up fallen leaves or use a lawnmower or electric leaf rake to chop them up to speed up the process. Put the damp leaves into sturdy plastic bags and poke air/drainage holes in the bag with a fork or build a simple wire-mesh cage. Leave these in a dark, undisturbed part of the garden for at least four to six months and let Mother Nature do the work for you, leaving you with a rich, crumbly compost to use the following year.
Top Soil and Lawn Dressing Enriched soil:
Topsoil is available in 25kg bags up to 880kg bags. You need to ensure when buying bulk bags, it is well screened and not full of weed seeds and stones. Small 25kg bags are ideal for spot repairs to lawns, potting and topping up small, raised beds but as a bag of soil does not go far, it is sometimes more economical to buy a larger bag (from a builder’s merchant may be less expensive). If you do not require all the soil, you may be able to share with a neighbour.
Lawn dressing enriched soil, sometimes called top dressing, is a premium blend of high-quality top soil, sand and organic matter (compost) which is pre-mixed with lawn-feed. You can use it to fill in dips, hollows and shallow spots in a lawn to create a smoother surface for mowing. It will also help to improve drainage and aeration if used once the lawn has been spiked. As it is enriched with nitrogen, it delivers nutrients to the grass root zone which will promote greener, thicker turf. This soil is used when reseeding a lawn or laying new turf.
Composted bark:
Composted bark is a natural organic material made by shredding tree bark and allowing it to decompose. It is widely used in gardening and landscaping as a mulch and soil conditioner, prized for suppressing weeds, retaining soil moisture, and gradually enriching the soil as it breaks down. It helps improve aeration in heavy clay soils whilst increasing water density in sandy soils. It also acts as an insulation barrier keeping roots cool in summer, preventing water evaporation and offering protection from winter frosts.
