The story of compost, peat and how to choose what's best for your plants and the environment
Let's start with the basics. The story of compost and peat, and why it's so important to make the right choice when buying soil for your plants and garden.
Peat
Peat is the surface organic layer of a soil that consists of partially decomposed organic matter, derived mostly from plant material, which has accumulated under conditions of waterlogging, oxygen deficiency, high acidity and nutrient deficiency. Peat formation is the result of incomplete decomposition of the remains of plants growing in waterlogged conditions. This may happen in standing water (lakes or margins of slow flowing rivers) or under consistently high rainfall (upland or mountain regions). As a result, partially decomposed plant remains accumulate and become compacted, forming peat that changes the substrate chemical and physical properties leading to a succession of plant communities. Peat is one of the most valuable natural occurrences on planet earth. Apart from being one of the biggest carbon absorbing masses when wet, peat is a valuable asset for wildlife and archaeology. To be of benefit though, peat must be wet and remain wet. In its dry state it becomes unstable and causes more harm than good. In the UK, peat and its vegetation has, for centuries, been cultivated, drained and degraded, leading to dry peat. Dry peat can be washed away leading to eroded plains, or catch fire in extreme heat leading to wildfires. Once upon a time, dry peat was an energy source because it burns so well. Dry peat releases carbon dioxide and is one of the biggest sources of greenhouse gas on the planet. In order for peat to be useful it must have an instrumental value. i.e a value which has a material benefit to another. These are generally; regulation, carrier, production, informational, transformational and intrinsic. For the UK, the instrumental values most important to us are regulation and informational. There is a wealth of information of the internet about peat and its value to the planet. You can read detailed information on the International Peatlands Organisations website here peatlands.org/ and detail about how the UK Government is planning to restore and preserved our peatlands here www.gov.uk/government/publications/england-peat-action-plan
Compost
Compost is simply decayed organic matter. It is NOT however, the same as soil, and it's really important to remember this when choosing the right substrates for plants.
Soil is the top layer of the earth, made up from sand, silt, clay and minerals and nutrients. Soil exists all over the planet and is made by nature. Soil changes depending on the habitat. From pure clay created by rock degradation, to humus rich soils found in tropical rainforests formed by fallen plant matter, soil is rich and varied.
Compost on the other hand, is a 'made' product, and is usually formed from plant (including paper) and uncooked food waste, built up over time and left to slowly decay. Eventually it will form a nutrient rich substrate which we use to add organic matter to the soil and improve drainage and water retention.
Compost is nutrient rich, darker in colour and generally looser in texture | Soil is general nutrient poor and sandy, gritty or clay |
Choosing the right substrate
So now you know the difference between the three basics, soil, peat and compost, it should make it easier to understand what your particular needs are when re-potting indoor plants, or digging the garden. Now let's look at the needs of particular plants
Indoor plants need very specific growing conditions to do well. Remember that there is actually no such thing as an 'indoor' plant. All plants grow outside, somewhere in the world. We simply grow them indoors when our climate doesn't match that of the plants natural environment. Tropical plants are a great example. Tropical plants we grow indoors in the UK are quite happily grown outdoors as ornamental plants in countries that mimic their native habitat, like the Bird of Paradise, for example. Within this group of plants, certain species will also need different composts, depending on their natural habitat. We have broken down indoor plants to their specific categories and grouped them together for their compost needs, as generally speaking each species that's from a similar climate will require similar needs. These are Tropicals and Aroids, Arids, Temperate.
Aroids & Tropicals
The most common tropical/ aroid indoor plants include:
Alocasia
Philodendron
Anthurium
Strelitzia
Dieffenhachia
Ficus
Howea
Spathiphyllum
Schefflera
Orchids
Alocasia, philodendron, anthurium, calathea, maranta and dieffenhacia and other aroids, all require similar care. Bright indirect light, watering when the soil is dry, and humus rich, free draining soil. This should generally be made up from a good quality compost or coco coir, fine bark and perlite. In the shop I make my mix with compost and fine bark. I also add charcoal to help with bacteria control. We use Melcourt in the shop. This compost is endorsed by the RHS, is sustainable and an excellent substrate for nearly all plants. To make it even more suitable for tropical plants, extra bark is added to provide the free flowing medium tropicals need. Strelitzia - Bird of Paradise actually need a very different soil due to their natural habitat being open, sunny and compacted. BOPs are native to South Africa, but are also in Mexico and the archipelago as an introduced species. BOPs are actually not to fussy about their soil but a loam based soil is preferred. Loam is what most gardeners would dream of having in their gardens! A good mix of clay, sand and silt. Apart from the sand, its pretty hard to get your hands of clay and silt to make compost, but don't go digging any from your garden either! A good quality compost from the garden centre will do just fine as long as its free flowing and allows for drainage. If you can buy loam then even better. Ficus - you will generally find across the internet information saying that figs are really easy plants to grow. But in our experience this is not true! They are temperamental and fussy and can be quite difficult to get to know. Ficus like a free flowing loam based soil, much like the BOP. But unlike the BOP, they shouldn't be overwatered as this can be fatal. Ultimately, a good quality mix compost with excellent drainage is needed. Howea (Kentia Palm) and Spathiphyllum (Peace Lily) - Kentias and Peace Lilies are actually pretty easy going. Suitable compost for them is a general purpose compost with some extra aeration like horticultural sand or grit, or even some fine bark. Schefflera - Umbrella Plant - The umbrella plant likes rich soil and humidity so choose a good quality compost for indoor plants. These can also be grown outdoors so if you're doing that then enrich your chosen planting spot with organic matter. Mushroom compost is good for this or even bagged manure from the garden centre if you don't have your own compost. Orchids - Orchids are completely different to all of the above plants simply because by nature they are epiphytes. These are plants that live on other plants. Orchids will grow on trees, using their roots to cling on and scramble around their host. Because of this, orchids do NOT need soil like other houseplants, and in-fact planting them in soil will eventually kill them. Orchids need only a bark to grow, or even just being attached to a piece of wood as a display. The bark should be in medium sized chunks. You should plant orchids in transparent containers to allow sunlight to reach their roots. Orchid roots should be plump and very light green in colour to be healthy. Shrivelled roots that are silvery coloured are not healthy!!
Arid Plants
All of these plants have in common the need for free draining, poorly watered, gritty soil. These plants will store moisture in their leaves so overwatering is generally fatal. A mix of sand, grit and a little compost is all that's needed for these genus of plant. It's worth remembering that as these plants require very poor soil, during the growing season you will need to feed them with a cacti/ succulent feed, to keep them healthy.
Temperate Plants
Temperate zones of the world are not too hot, not too cold, not too wet, not too dry. They occur between the tropics and the poles in both hemispheres. We also find temperate pockets in unexpected places such as high up on mountains in the tropics or on remote tropical islands. Temperate regions are also where most of us live, build our cities and clear land for agriculture. Plants native to temperate areas are at the frontline of global change and many of the risks they face are caused by humans. (credit to Kew Gardens for this text). Temperate plants are some of the most at risk, rare or extinct plants in the world due to their habitats being destroyed for human habitation and production. Kew Gardens has the largest temperate Victorian greenhouse in the world and houses some 1500 species, some of which are extinct in the wild. You can read more about their temperate house on their website Temperate House | Kew Gardens
As such, most plants we can buy in the UK won't be temperate plants, although there are a few exceptions.
Aloe Jucunda - a miniature aloe, it can be purchased as a houseplant, but in its native home on the upper slopes of the Ga’an Libah Plateau in northern Somalia, it is at risk of extinction. Its natural growing soil is actually limestone where its forest habitat of A.jucunda has been all but obliterated by intensive livestock grazing, wood-cutting and charcoal burning. Somalia does not have any protected areas so its habitat continues to be under threat. This plant prefers very poor soil - either just grit, or a mix of sand and grit.
Clivia miniata - Bush Lily - South Africa’s most iconic plant, Clivia is threatened in the wild by overharvesting for horticultural and medicinal purposes. They are grown for their bold strap-shaped, dark-green leaves and trumpet-shaped red, yellow, orange or cream flowers borne in groups on stout stems. Clivia like well-drained, loam-based John Innes No 2 compost mixed with multi-purpose compost or additional leaf mould and grit, although any good potting medium should be satisfactory. Do not plant too deeply – the neck of the bulb should be above soil level.
Begonia - Native to South America, Central America, Central Africa and South Asia, begonia come in a myriad of species and colours. They like loam based compost which is well drained. As with Clivia, they would appreciate a good quality indoor compost with added drainage like grit.
Ferns - most ferns are from temperate regions, including the UK although our native ones can obviously be grown outdoors. House ferns like the Boston Fern or Rabbits Foot Fern are best grown indoors. Ferns prefer a humus rich soil that remains constantly moist but not wet. A good compost with added humus like leaf mould would be a good choice.
Outdoor Plants
Like indoor plants, outdoor plants also need different soil needs according to their species. Acid loving plants - Rhododendrons, camelia, azalea will need what's called an ericaceous compost. Use John Innes ericaceous compost or mix a peat-free ericaceous compost with neutral or acidic topsoil. Tubs, baskets, patio planters, leafy salad plants, flowering bedding plants - a general multi purpose peat-free compost is suitable for most of these plants. You can buy specific composts for these which generally have some kind of water retention additive to help keep the soil moist in containers, but if you are happy to keep them watered regularly a standard compost will do. Seedlings and sowing - sowing and raising seeds is a specific job that needs specific compost. Compost for sowing is very fine and generally low in nutrients.
This is because fine shoots from seedlings need a completely fine substrate to push through, and high levels of nutrients can be detrimental to seedlings. This compost will be marked as seedling/ sowing compost.
General garden plants - perennials, ferns, wildflowers, etc - these plants will be fine with a general purpose peat-free compost. Depending on what you're planting you may need to add other ingrediants like mushroom compost or manure. For instance, ferns like a more humus rich soil that other garden plants. Fruit and Vegetables - a standard compost is fine for most vegetables when mixed in with your garden soil. Growbags are good for tomatoes, chillies, peppers and other nightshade-family fruits, as well as soft fruits. Carrots need a well drained, fine tilth (no stones or other debris) to grow well. Stones and other debris in the soil can lead to wonky carrots that don't grow well, as do parsnips. Citrus - citrus plants like lemon and orange need a specific compost which is available from good garden centres. With a perfect balance of nutrients, this type of compost uses Seramis clay granules that work to maintain water absorption. It also contains loam to help retain enough nutrients to develop high-quality fruit trees that you can enjoy for years to come.
You can find specific soils for indoor and outdoor plants in our shop