Compost: complete guide to types, uses and selection

Garden compost, multi-purpose compost, peat-free compost, John Innes compost, ericaceous compost – the terminology suggests these materials are interchangeable variations on a theme. They are not. Each type represents a distinct formulation designed for specific applications, and using the wrong type in the wrong situation produces predictable failures regardless of plant selection or aftercare quality.

Understanding what compost actually is, how different formulations behave, and which situations require which type determines whether container plantings thrive for years or fail within months, whether raised beds remain productive or become waterlogged and anaerobic, and whether ericaceous plants flourish or exhibit the chlorosis and dieback characteristic of inappropriate growing media.

This guide explains compost types available in Kingston, Surbiton and Surrey, when to use each formulation, how to identify quality products, and why certain applications demand specific compost specifications that cannot be substituted without consequence. It sits within our wider garden advice section, alongside our soil, compost and growing media guide and topsoil complete guide.

What is compost?

Garden compost is decomposed organic matter – plant material, wood fibre, peat, coir, bark, or green waste broken down by microorganisms into a growing medium. Crucially, compost contains minimal mineral particles. It is almost entirely organic material in various stages of decomposition.

This distinguishes compost from soil and topsoil in fundamental ways. Soil contains 85–95% mineral particles (sand, silt, clay) plus 3–8% organic matter. Topsoil is natural soil excavated from the upper soil layer, mineral-based throughout. Compost, by contrast, is 90–98% organic matter with minimal minerals.

This compositional difference creates fundamentally different behaviour regarding structure, drainage, water retention, and longevity. Compost is a temporary material that continues decomposing, compressing, and losing structure over 12–24 months. Soil is a permanent material with stable mineral skeleton that persists indefinitely. Treating these materials as equivalent – using compost where soil is required or vice versa – produces the kind of failures that account for a significant proportion of disappointing planting outcomes.

For detailed comparison see our compost vs soil guide and compost vs topsoil guide.

Multi-purpose compost

Multi-purpose compost is the most widely used growing medium in domestic gardening, traditionally peat-based but increasingly formulated with wood fibre, green waste compost, or coir as peat alternatives. Quality and performance vary dramatically between brands and formulations.

The characteristics of standard multi-purpose compost include light weight and easy handling, good initial drainage and aeration, a nutrient charge that lasts 6–8 weeks before requiring supplementary feeding, and structural integrity that collapses progressively over 6–18 months depending on quality. Once structure fails, the compost becomes either hydrophobic (refusing to rewet) or waterlogged (losing air spaces) – both conditions fatal to plant roots.

Multi-purpose compost performs well for seasonal bedding plants replaced annually, short-term containers for summer displays, seed sowing and propagation, and annual vegetables grown in containers. It is unsuitable for permanent containers housing shrubs or perennials, raised beds expecting multi-year use without rebuilding, and ericaceous plants which require acidified growing media.

Quality indicators when buying multi-purpose compost include consistent texture throughout the bag with no large uncomposted wood chips, pleasant earthy smell rather than sour or ammonia notes, moderate moisture content (not bone dry or saturated), and absence of weed seeds. Budget multi-purpose compost from supermarkets typically uses lowest-grade materials with minimal nutrient charge, and structure fails faster (6–12 months versus 12–18 months for premium products). This is false economy for anything lasting beyond one growing season.

Peat-free compost

Peat-free compost formulations have become increasingly important as the environmental cost of peat extraction has gained recognition. Peat extraction destroys rare lowland bog habitats that take thousands of years to form, and the UK government has committed to phasing out retail peat sales. Peat-free formulations eliminate this environmental cost but perform differently and require adjusted expectations and management.

Peat-free compost is typically formulated from wood fibre, green waste compost, composted bark, coir, or combinations thereof. The characteristics vary depending on the specific formulation but generally include variable water retention dependent on the formula, a critical tendency to become hydrophobic when dry (particularly wood fibre-based products), faster decomposition than peat-based equivalents with structure failing within 6–12 months, sometimes inconsistent nutrient availability, and dramatic shrinkage in some formulations (30–40% volume loss in the first growing season).

The hydrophobic behaviour of dried wood fibre-based peat-free compost is the most significant practical issue. When the compost dries completely, water beads off the surface rather than penetrating, making rewetting extremely difficult. This makes peat-free compost particularly unsuitable for containers prone to drying, hanging baskets, and situations where consistent moisture cannot be guaranteed.

Peat-free compost works well for seasonal bedding and annual planting where structure longevity is unimportant, when environmental priorities outweigh performance differences, and when mixed 50:50 with loam or topsoil for raised beds where the loam component provides permanent structure. Management requirements include vigilant watering to prevent complete drying, slow surface watering to prevent runoff, addition of water-retaining granules for full-sun containers, and acceptance of more frequent watering than peat-based equivalents demand.

For detailed explanation of hydrophobic behaviour see our peat-free compost drying guide.

John Innes compost

John Innes compost is fundamentally different in composition from multi-purpose products. Developed at the John Innes Horticultural Institution in the 1930s, the formula combines sterilised loam (topsoil), horticultural sand, and peat or peat substitute in specific ratios that vary by formulation.

Three standard John Innes formulations exist. John Innes No.1 contains low nutrients suitable for seedlings and rooted cuttings. John Innes No.2 contains medium nutrients for potting on and general container use. John Innes No.3 contains higher nutrients designed for established plants and long-term containers.

The critical advantage of John Innes compost is the loam component, which provides permanent mineral structure that multi-purpose composts lack. This translates to several practical benefits: significantly heavier weight that stabilises top-heavy plants, structure that persists for years without collapse, consistent nutrient availability from the loam’s cation exchange capacity, no hydrophobic behaviour, and reliable performance for plants remaining in containers for multiple years.

John Innes compost suits permanent containers housing shrubs, trees, or perennials, plants remaining in the same container for two or more years, top-heavy specimens requiring ballast, and professional growing where structure longevity matters. It is less suitable for weight-sensitive applications (roof gardens, hanging baskets), and represents unnecessary expense for short-term bedding displays.

Quality matters significantly. The John Innes specification is not trademarked, and quality varies dramatically by manufacturer. Look for products explicitly stating “to John Innes specification” from reputable suppliers, and treat with caution products that use the name without the specification reference.

Ericaceous compost

Ericaceous compost is acidified growing medium formulated for lime-hating (calcifuge) plants. Standard composts and most garden soils sit in the pH range 6.0–7.0, broadly neutral. Ericaceous compost is formulated to pH 4.5–5.5 – significantly more acidic.

Plants requiring ericaceous conditions include Rhododendron and azaleas, Camellia, Pieris, Vaccinium (blueberries), heathers (Erica and Calluna species), and certain other genera adapted to naturally acidic soils.

The reason pH matters comes down to nutrient availability. These species evolved on acidic soils and have developed specific nutrient uptake mechanisms adapted to those conditions. On neutral or alkaline substrates they exhibit lime-induced chlorosis – leaves turn yellow with green veins, growth stunts, and plants progressively decline. This is not nutrient deficiency requiring feeding but pH-induced nutrient lock-up requiring acidic growing medium. Adding fertiliser to chlorotic ericaceous plants in standard compost produces no improvement because the nutrients are present but unavailable at the wrong pH.

Using standard compost for ericaceous plants produces chlorosis within 6–12 months regardless of feeding regime. The reverse situation – using ericaceous compost for lime-tolerant plants – wastes money but causes no direct harm. The error is one-directional.

An important consideration is that ericaceous compost pH rises over time as organic acids decompose. Within 12–24 months, an ericaceous mix may have risen above pH 6.0, at which point lime-induced chlorosis begins. For long-term ericaceous containers, annual top-dressing with fresh ericaceous compost or incorporation of sulphur chips maintains acidity over the longer term.

For detailed information on pH and nutrient availability see our soil pH and nutrient lock-up guide.

Specialist compost formulations

Several specialist composts exist for specific applications, each addressing requirements that standard composts cannot meet.

Seed and cutting compost is fine in texture with low nutrient content. The low nutrients prevent scorching of delicate seedlings and emerging roots, while the fine texture provides excellent contact between seed and growing medium. Using standard multi-purpose compost for seed sowing produces significantly higher failure rates.

Aquatic compost is heavy, low-nutrient formulation designed to prevent flotation and algae proliferation in ponds and water features. Standard compost used in pond baskets floats, clouds water, and encourages algal growth.

Orchid compost is bark-based and extremely free-draining, reflecting the epiphytic origins of many cultivated orchid species. Standard compost drowns orchid roots within weeks.

Cactus and succulent compost contains high proportions of sand and grit with minimal organic matter and very free drainage. Standard compost retains too much moisture and rots cacti and succulents reliably.

When to use compost versus soil versus topsoil

The choice between compost, soil, and topsoil is not a matter of personal preference but a matter of matching material characteristics to application requirements.

Compost is the correct choice for containers and pots where the temporary nature of the medium is acceptable (replacement every 12–24 months is normal container maintenance), seasonal bedding replaced annually, seed sowing using specialist seed compost, and raised beds when mixed 50:50 with topsoil to combine compost fertility with topsoil structure.

Topsoil is the correct choice for raised beds requiring permanent mineral structure, lawn establishment creating stable rooting medium, levelling and grading where stability matters and settling cannot be tolerated, and replacement of contaminated or fundamentally unsuitable existing soil. See our complete topsoil guide for detailed specifications.

Soil conditioner is the correct choice for improving existing soil through annual incorporation, annual mulching to maintain organic matter content, and mixing with topsoil for raised beds at typical ratios. See our soil conditioner vs compost guide for detailed comparison.

Pure compost should never be used for permanent raised beds (structure collapses within 2–3 years), ground-level planting (expensive and inappropriate compared to improving existing soil), or lawn establishment (wrong particle structure, settles excessively).

How to identify quality compost

Visual inspection at the point of purchase reveals significant quality differences. Quality compost shows consistent texture throughout the bag with no large uncomposted chunks or wood chips, appropriate moisture content (neither bone dry nor saturated to the point of running), no white fungal growth (which indicates poor processing or storage), minimal weed seeds (which suggests inadequate quality control), and a pleasant earthy smell rather than sour, ammonia, or rotten notes.

Label information indicates manufacturer confidence in the product. Quality composts list ingredients transparently, specify nutrient content (NPK values for fortified products), state accurate volume measurements (50 litres should be genuinely 50 litres rather than compressed), and may include use-by dates as nutrients degrade in long-term storage.

Brand reliability matters in compost selection. Professional growers use consistent brands because compost quality directly affects crop success. For domestic use, established brands including Westland, Levington, Dalefoot, and Melcourt offer more consistent quality than budget supermarket products. The price difference between budget and premium compost is small in absolute terms but the performance difference is significant.

For peat-free compost selection, formulations vary dramatically between brands. Wood fibre-based products from Dalefoot and Melcourt perform significantly better than many budget peat-free composts. Trial small quantities of unfamiliar brands before bulk purchasing for important projects.

Where to buy compost in Kingston, Surbiton and Surrey

For domestic quantities, garden centres provide the widest range with knowledgeable staff available for advice. Squires Garden Centres at Twickenham, Long Ditton, and Shepperton stock comprehensive ranges with helpful advice. Hillier Garden Centre at Windlesham offers premium products. Notcutts Garden Centre at Bagshot maintains a comprehensive selection.

For larger quantities, bulk suppliers offer significant cost savings. Bourne Amenity delivers bulk compost and topsoil throughout Surrey. Bury Hill Landscape Supplies provides professional-grade products with delivery to Kingston, Surbiton, and surrounding areas. Topsoil Direct delivers across Surrey with online ordering.

Bulk compost (loose load or bulk bags) costs 50–70% less than bagged compost for large projects. Most suppliers deliver with a minimum order of 1 cubic metre. Quality varies considerably between bulk suppliers, so specify requirements clearly and inspect samples before accepting delivery of significant quantities.

Common compost problems and solutions

Compost dries out and refuses to rewet

This is the classic peat-free compost failure, particularly with wood fibre-based formulations. Once completely dry, water beads off the surface and runs around rather than through the compost. Prevention through vigilant watering before complete drying is more effective than recovery once the problem has occurred. Recovery techniques include adding a drop of washing-up liquid to water as a surfactant to break surface tension, complete immersion of containers in water buckets for 30 minutes to rewet from the bottom, and acceptance that subsequent watering must be more frequent. For containers prone to drying, switch to peat-based or John Innes formulations which do not exhibit this behaviour.

See our detailed peat-free drying guide.

Plants decline after 12 to 18 months despite regular feeding

This indicates structural collapse rather than nutrient deficiency. As compost decomposes further, organic particles become finer, pore spaces compress, drainage slows, and aeration deteriorates. Roots require oxygen as well as nutrients, and in structurally collapsed compost they suffocate in anaerobic conditions regardless of feeding. The only resolution is repotting into fresh compost with proper structure. For permanent containers, switch to John Innes formulations where the loam component provides structure that persists for years rather than months.

See our guide to why plants die in pots.

Compost shrinks dramatically in containers

Organic matter decomposition reduces volume over time. Some peat-free formulations lose 30–40% of their volume in the first growing season as material decomposes. The solution is annual top-up with fresh compost, mixing compost 50:50 with loam or John Innes to reduce shrinkage rates, and acceptance of this as an inherent characteristic of organic growing media rather than a product defect.

Ericaceous plants turn yellow despite ericaceous compost

This typically occurs 12–24 months after planting as ericaceous compost pH rises through decomposition of organic acids. Once pH exceeds 6.0, lime-induced chlorosis develops. The solutions include annual top-dressing with fresh ericaceous compost, watering with rainwater rather than tap water (which raises pH in many areas), and incorporation of sulphur chips to maintain acidity over the longer term.

How Flourish specifies compost for clients

Choosing the right compost for a planting project requires understanding what the planting needs to achieve over what timescale, what the container or growing situation demands, and what maintenance commitment is realistic for the client. We specify compost formulations as part of our planting design and installation work, drawing on Craig Davis BSc (Hons) Horticulture’s three decades of experience with compost performance on Surrey garden projects.

For permanent container plantings – the structural Buxus, the topiary specimens, the long-term feature plants – we specify John Innes No.3 with sharp sand drainage layer rather than multi-purpose compost. The initial cost is higher but the structure persists for years rather than months, and the plants succeed where they otherwise routinely fail.

For raised beds we specify topsoil mixed 50:50 with compost or soil conditioner rather than pure compost, providing the permanent mineral structure that allows beds to perform for decades rather than the 2–3 years that pure compost permits. See our garden design and build service for project examples.

For seasonal bedding, multi-purpose compost is entirely adequate – the temporary nature of the planting matches the temporary nature of the medium. Specifying John Innes for seasonal bedding wastes money without performance benefit.

Book a consultation with Flourish Landscaping to discuss compost specification for your specific project.