How to choose the correct compost
A guide to choosing the correct compost!
There are many different types of compost available to help you grow a range of plants that are unsuitable for your ordinary garden soil. Compost is full of nutritional balances for specific plants and growing purposes.
Plants in hanging baskets, for example, need suitable potting compost that’s specially formulated to attend to their growing needs, by providing the correct balance of nutrients, helping along healthy root growth, and allowing the plant to anchor it well. The compost needs to be open enough to allow air to the roots and surplus water to drain, yet sufficiently binding to keep enough water in.
Peat reduced and peat-free products.
For years, peat-based potting composts have been used to raise and grow-on plants. However, peat is primarily sourced from lowland raised bogs- an increasingly rare habitat in the UK and Europe- and in recent years, it’s been highlighted that this precious natural resource needs protecting!
Compost manufacturers have quickly responded by producing and increasing ranges of peat-free and peat-reduced growing compost containing mixtures of organic materials such as bark, wood fibre and green compost- mixed with inorganic materials such as grit, salt, rock wool and sharp sand. A mix of coarse and fine particles is essential to create the perfect environment with enough water and air, essential for healthy root growth.
So, if you’re keen on helping the environment, ensure to select a peat-reduced or better, peat-free compost. Manufacturers are constantly working to improve the blend quality, and have all the information you need on the packaging if you’re unsure.
You’ll notice that peat-reduced and peat-free brands of compost often recommend certain brands of fertiliser to use with the compost. This is not just some advertising ploy, they’re recommended because of their nutrient balance, as different formulations have varying NPK (Nitrogen, Phosphorous and Potassium) ratios. Use either the recommended product, or look for a fertiliser with a similar NPK balance to the compost, and you can’t go wrong.
Potting composts: what to choose?
Whether you’re sowing seeds, planting hanging baskets or potting up, it’s essential to choose the right type of compost. The range of potting compost available on the market now seems to be forever growing, varying in price, green credentials, added extras and supposed results. Multi-purpose compost always seems the obvious choice, but it might be worth checking out other types available, to help provide your plants with the best chance of success.
We all know the benefits of choosing multi-purpose composts! It’s cheap, holds water and nutrients well, and it’s suitable for just about everything from bedding plants to raising young potted plants. Multi-purpose compost doesn’t contain any soil or loam (a mixture of sand, clay and silt) but is full of peat or peat-substitutes (organic waste or wood fibre) mixed together with sand, perlite, bark chip or vermiculite for added drainage and aeration (More on these in a bit)! Multi-purpose compost makes a great soil improver, but is mainly used for single season bedding.
Loam? Basically, it’s a mixture of sand, clay and silt, and is commonly known as the basis of John Innes compost. It’s the most easy to use compost for permanently planting containerised trees, shrubs and perennials, due to its heavier weight, providing good anchorage. Made from sterilised loam, peat and grit with added lime and fertilisers, it was developed by the John Innes institute in the 1930’s. There are three different types for different purposes. John Innes No. 1 has the least fertiliser, suited to short-term potted plants. John Innes No.2 has more nutrients, suited to permanent pot plants with low fertiliser needs. John Innes No. 3 has the most fertiliser for a wide range of permanent container plants. So there’s no one type of “loam-based compost” but there is something for just about everything!
Specialist Compost: Why not to choose Multi-purpose every time!
Some plants have much more specific compost needs. From varying on drainage needs to acidity likes or dislikes, there are all sorts of recommended do’s and don’ts!
The term “Ericaceous” refers to acid-Loving, lime-hating plants! Acid-loving plants such as rhododendrons, azaleas, heathers and camellias need ericaceous compost, which are a peat-based mix with less added lime and different fertilisers from multi-purpose compost. If they are simply potted into multi-purpose composts, ericaceous plants can turn yellow, with blotches appearing on leaves which can turn brown, due to too much chalk and lime in the potting mixture. Manufacturers are working to try and create a peat-free or peat-reduced recipe, suitable for acid loving, lime-hating plants. Larger ericaceous trees and shrubs are often easier to manage in John Innes ericaceous compost.
Aquatic compost or “pond compost” is made from sterilised loam and grit to anchor pond plants down in the water. With a controlled-release fertiliser that feeds the plants, it prevents the nutrients from leaching into the water and causing dangerous algal growth. So it’s quite simple really!
Awkward Orchids need free draining specialist compost, with added bark chips. Watering orchids can often become a difficult task, as they hate holding on to water for too long. The aerated orchid compost allows for their roots to find daylight easily, and for the water to drain quicker.
Cacti always do best in an extra-gritty, sharply draining Cacti Compost Mix. Not keen on being over-watered, Cacti like porous compost which drains quickly and easily. Cacti Compost contains the essential nutrients required, and trace elements to build strong and healthy plants.
Bonsai naturally grow with a lack of nutrients surrounding their roots. When it comes around to re-potting them, Bonsai need the right balance of aeration, water retention and drainage to ensure that they continue to develop a healthy root system. Bonsai compost is specially formulated to the right consistency, and balance of nutrients to ensure that they remain healthy and continue to grow.
Citrus compost is recommended for potting orange, lemon and lime trees, due to its unique balance of nutrients to ensure a healthy root system, and growth pattern. Citrus trees require loam-based compost with added bark chippings to ensure easy drainage. Citrus trees hate to be over-watered, and should only require watering once the compost has almost completely dried out.
What can I add to compost to get even better results?
There are various materials which can be added to potting composts to improve the mixture, making them more suitable for growing certain plants. We mentioned on these weird and wonderful terms earlier, so here’s a bit more info!
Man-made, vermiculite is produced by heating a type of clay to 1,000°C for one minute, causing the mineral to expand and produce a sponge-like texture. Vermiculite is completely sterile, contains essential nutrients, and improves both drainage and water-retention in the compost. When sowing any seeds, use any seed-sowing compost, and cover with a fine layer of vermiculite to help create a humid, warm and aerated environment which is perfect for germination.
Perlite is a man-made product, produced by crushing and heating volcanic glass to 1,000°C, causing it to expand into a light shell filled with air. This is the perfect material for opening up the compost, creating a porous consistency and improving drainage. This is a handy tool to have throughout the winter, as heavy rain can cause plants to drown in water-logged soil and pots. It’s recommended to use a mix of 70% soilless compost, and 30% perlite.
A natural material derived from rock, horticultural grit opens up the compost, creating a more porous texture for good drainage. Its weight means that the compost becomes heavier, providing good anchorage for more permanent plants. Many popular shrubs, perennials and bulbs come from Mediterranean areas with naturally stoney, dry and well-drained soils, so mimicking these conditions over here will ensure they continue to thrive. The recommended mix is three parts grit with 7 parts multipurpose compost. Bulbs in particular benefit from a 2.5cm layer of grit placed at the base of the planting hole to further aid drainage.
Hellebores, bergenias, ferns and heucheras are otherwise known as woodland perennials, which like moist but well drained soil, rich in organic matter. They can be grown in containers, using multi-purpose compost with added bark chips. These will improve overall drainage while allowing the compost to remain moist and cool, sustaining healthy plant growth.
If you know of any tricks of the trade, or have any comments about using different types of compost- tell us! We always welcome your comments- so feel free to leave one below.