How to tell the difference between all the compost in the garden centre

Use the correct compost for a blooomin' garden with happy healthy plants

Hanging basket planted with fuchsia, calibrachoa and nepeta (pictured above)

Compost is the essential component for growing plants, except air plants and those grown using a hydroponic system. Different plants have different requirements, some acid loving plants, such as rhododendrons and azaleas absolutely must have an ericaceous compost, which is an acid compost. But some plants which prefer ericaceous compost, such as magnolias and Japanese maples, will tolerate a neutral compost provided it has plenty of nutrients and is well draining. Some plants, such as alpines, need a very free-draining compost so it must be mixed with sharp sand or horticultural grit to open up the structure enabling the water to drain away.

If you use a mature plant compost for sowing seed the added food can be too strong for the tender seedling and will kill it; too much fertiliser can be just as harmful as not enough. Seeds also need a fine compost without any large pieces of organic matter as they may not be strong enough to push past that twig or piece of bark. Once you have germinated your seeds and they need potting on they also need a fine grained compost so that their roots can grow freely and make a strong plant. So all in all it is essential that you use the correct compost for your plants.

A trip to the garden centre for simple compost can result in being out-faced with a bewildering assortment of growing medium. There are specific composts for plants such as rhododendrons, azaleas, camellias, conifers, roses, houseplants and bedding plants, so if you are planting any of these then the choice is simple but for planting anything else then it is a minefield if you are a beginner gardener.

Magnolia watsonii

Seed compost

This is a very fine grained compost, usually with no or very little added nutrients as seeds already come with their own food source inside the seed shell. The Gro-Sure Seed & Cutting compost contains Vermiculite, a very light natural substance, which aids germination. It also contains a small amount of nutrients and seaweed extract to give the young plants a good start in life. This compost is also used for cuttings so you don’t need to buy another compost mixture. It usually comes in various sizes ranging from 8ltr – 30ltr so if you are only doing a couple of tray of seeds you don’t have to buy a massive bag and then find somewhere to store it.

Cutting compost

This is a very free-draining mix, usually with added Vermiculite or Perlite to keep the weight down and stop the compost grains sticking together. You can make your own by mixing 50% potting compost with 50% sharp sand or Perlite. Again this is available in various bag sizes from 8ltr – 30ltr.

Potting compost

Again this is a free draining mixture but with a fertiliser added, usually slow release which will feed the plant for 3 months until it is big enough to go out into the garden. This is available in sizes ranging from 8ltr – 40ltr and is used when your seedlings have got to the stage where they need taking out of the tray and potting on into an individual cell or pot. It can also be used for houseplants.

John Innes No 1

John Innes is usually loam based but this is becoming increasing more difficult to source so they now have a significant peat or peat substitute component. The No 1 mix has the least amount of nutrients and is suitable for potting on young plants. It is available in 8ltr – 40ltr bags.

John Innes No 2

This has twice as much nutrients as the No 1 and is used for more established plants such as container grown vegetables which don’t require large amounts of fertiliser, spring and autumn bedding plants and houseplants.

John Innes No 3

The No 3 mix has 3 times as much fertiliser added than the No 1 and is for mature plants, shrubs, trees, summer bedding plants and greedy vegetables such as tomatoes, cucumbers and potatoes.

Multi-purpose compost

Multi-purpose is the general all-round compost for using in containers, as a soil improver, particularly if you have heavy clay or light sandy soil, or as a mulch in autumn. Use it for growing mature plants, vegetables, fruit, shrubs, trees, bedding plants or herbaceous perennials. Its main component is usually peat, but there are alternatives available. It usually comes in bags from 20ltr – 80ltr and is generally the cheapest compost. A few brands also include water retention gel and controlled release fertiliser. If using it for containers you will have to incorporate some controlled release fertiliser which will feed your plants over a 6 month period.

Cauliflowers growing in a raised bed

Organic compost

Organic compost is made from organic matter which has been grown organically and not treated with any chemicals, inorganic fertilisers, pesticides, herbicides or fungicides. True organic compost bought in the garden centre ready bagged is usually the most expensive option. You can make your own if your garden is organic, but we sell a brand called Lakeland Gold which is not strictly organic but as near as you will get at a reasonable price. It is made from sheep wool, off the producers own flock which graze the Lake District fells, and bracken, which poses such problems for the hill farmer. There are different blends available for seeds, ericaceous plants, vegetables, breaking up heavy clay soil and standard compost for mature plants. It comes in 30ltr bags.

Peat-free compost

You have to be careful buying peat-free compost as it is often council waste (green waste), which can be low grade containing all sorts of contaminants such as plastic, string and glass, so never go for a really cheap product. They are often blends of several different materials such as coir, green waste and composted sawdust. Use it for more mature plants and as a mulch in autumn.

Coir compost

One alternative to not buying peat-based composts is to buy coir compost which is made from the husk of coconuts but doesn’t have the same water or nutrient retention properties of peat and again is often blended with other materials. It can be purchased in a compacted block which has to be soaked in water for an hour or so, the advantage being that it is light to transport, and the more expensive blends also contain a controlled released fertiliser. It gives good results and you have the added knowledge that you are doing your bit to help the environment by preserving the last few remnants of lowland peat bogs, which are a scarce habitat supporting a unique collection of flora and fauna. It can be used for almost anything, but people experience mixed results when using it as seed compost.

Home-made compost

This is the cheapest way of obtaining compost but the quality can be variable depending upon what you have composted and how long it has been left to mature. It is used for planting mature specimens and enriching the flower border and vegetable beds. Any of the green waste from your garden can be used; if using grass clippings only add them in thin layers with other materials as they can become slimy and smelly. Other materials can be shredded paper, not the glossy pages of magazines as the ink used could be toxic, vegetable peelings, not cooked food as this will go mouldy and attract rats. If you are using woody material try and chop it up as small as possible. The heap must be turned every month as air is essential in producing lovely friable compost; if done correctly it shouldn’t smell. It usually takes at least 6 months to be ready to use, and should be dark brown and crumbly and smell like a damp wood.

Leaf mould

This is purely leaves placed in a black bin liner and left to rot for a couple of years. Some large leaves and those from evergreens will need chopping up first, just run over them with the lawn mower. Try not to add too many conifer needles as these will take a long time to break down. This is used purely to enrich the soil, just add as a mulch in autumn or if you have heavy clay or light sandy soil dig it in in the autumn.  

Soil conditioner

This is often a mixture of well-rotted farmyard manure and composted bark which you add to your soil to improve the organic content, it’s especially beneficial for heavy clay and light sandy soils but also enriches tired flower borders and the vegetable garden. It usually comes in large bags of 50ltrs and over.

Top soil

Top soil is the upper layer of soil and contains all the nutrients and organic matter so is the most important part of the garden, if you have poor soil then your plants will struggle. The top soil in established beds will very rarely need replacing as you just enrich the existing soil with compost or well-rotted farmyard manure. You really only need topsoil if you are laying a new lawn and the soil is poor and stoney, constructing a lot of raised beds or creating new beds where there is only a thin layer of soil, this is often the case with new-build houses where the soil can often contain builders rubble. It is available in large bags from the garden centre or if you need to cover a large area then it is better to go to a contractor for a lorry load or ton bags.

Farmyard manure

This is exactly what it says, it is manure which is mixed with straw and has been used for animal bedding. This cannot be used fresh so if you are in any doubt about how long it has been composting buy the bagged manure from the garden centre. It is best if it’s been left to rot for a couple of years, if you use it too fresh it could be too strong and burn the plant roots. Horse manure is the best as it contains the most nutrients but pig and sheep manure contain higher levels of nitrogen so are useful if used for leafy vegetables. Again use to add body and a few nutrients to your flower beds and vegetable garden; adding organic matter to the soil enables plant roots to penetrate more easily and so reach more nutrients and water, it also helps retain water on free-draining soils and heavy clay soils to drain more freely. It is available bagged from garden centres and directly from farms, just make sure you know where it has come from and that the animals haven’t been extensively dosed with chemicals.

Horticultural/potting grit

This is exactly what it says, sharp grit which can be used in a variety of ways. Use it mixed with compost to improve drainage for taking cuttings and especially when planting alpines either in the ground or in containers. It can also be used to top dress plants, again especially alpines, to stop the soil splashing up and marking the delicate blooms. When used as a top dressing it also stops the delicate plants from rotting at soil level. As the small stones are quite angular it makes an excellent slug barrier, just put a circle around vulnerable plants or stand containers on a layer of the grit.

Fritillaria michailovskyi

Sand

Sand for horticultural use is sharp and performs the same function as the grit, it just has a smaller structure. It’s not to be confused with play sand which is often on sale in the same area in garden centres as the composts; this is too soft. Don’t be tempted to use builders sand, which is cheaper, as it can contain chemicals and compounds which are detrimental to plant growth.

Perlite

This is derived from volcanic glass and is mainly used added to compost for growing cuttings as it retains a certain amount of moisture but also opens up the compost structure and so avoids compaction and water-logging. It also has excellent thermal properties so that the compost doesn’t swing between temperature extremes which can retard growth. Perlite can also be used alone for rooting cuttings. Also if considering a green roof where weight is an important factor combine a percentage of Perlite as it is extremely light.

Vermiculite

Vermiculite is used in the same way as Perlite; for seed sowing and potting on seedlings. Like perlite it also has very good heat and moisture retention properties and it also promotes faster root growth. It can also be used to pack dry bulbs and tubers in winter to protect them from extremes of temperature.  

Chipped bark

This is mainly used as a weed suppressant mulch, either applied in autumn or spring. Click here to read the blog explaining all about the benefits of mulch. It also makes really good garden paths, being non-slip; they will need topping up every 3 – 4 years as it will break down and become incorporated into the soil underneath.

Mini chipped bark

The mini chipped bark can be used in the same way as the ordinary bark but with the addition of using it as a soil conditioner. If you have heavy clay soil dig it in in autumn and let the winter weather break down the chips and the clods of clay. It serves the dual purpose of opening up the structure, allowing it to be better drained, and adding organic matter.