Confused by compost? Discover the best compost you can buy to help your seeds, vegetables and plants to thrive.
We're often asked about the best soil or compost to grow plants in, and with so much on offer, it's not surprising that most of us find growing mediums or soil confusing. But healthy soil is the first step to a blossoming garden and incredibly important for a bountiful crop, so it's worth taking the time to get right.
Visiting a local hardware store can be a daunting prospect for new gardeners. Working out which type of compost your plant baby needs often involves lifting and turning over each bag to read the instructions. This can be time-consuming, not to mention the upper body strength required!
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But many lack the space for homemade compost or are waiting for it to be in a useable condition. In the meantime, shop bought compost can be a good substitute if you know what to look for. Read on to unearth what makes great compost and discover the best compost to buy for your patch.
Healthy soil is the first step to a blossoming garden and incredibly important for a bountiful crop, so it's worth taking the time to get right. Photo: Gabi Miranda, Unsplash
How to choose the best multipurpose compost
Sold by most nurseries, this growing medium is a mixture of ingredients created to suit as wide a range of plants as possible. Every brand has their own mix, but the primary ingredient has traditionally been peat, due to its ability to absorb and release water and feed as required by plants.
Arguably, the best compost for containers is one that has been enhanced with additional nutrients, mixed throughout in the form of small yellow, white or blue balls. But you also add the pellets yourself. Osmocote works by releasing feed slowly over six months. It is commonly used in the horticultural industry as it reduces the waste associated with liquid feeds (which run straight out of the pot if done incorrectly!). In below video, Helen Lockwood explains how to use Osmocote and discusses its benefits.'
As we outline in our vegetable growing guide, the best compost for vegetables is a moist, well-draining mix that is rich in organic matter. Bear this in mind when choosing your compost.
What is peat and why is it bad?
Peat (sometimes called peat moss) is slowly falling out of fashion with growers, and for good reason. Only 10% of UK land cover is composed of peat, yet peatlands are more effective at storing carbon than our forests. When peat is extracted from bogs, it releases vast quantities of carbon into the atmosphere. Our peatlands are vital in the fight against the climate crisis but only if they stay in the ground.
What is the best Peat Free compost?
Aside from the environmental benefits, the advantages of peat free compost range from its moisture and nutrient retention abilities to its use as a soil improver. The voluntary target for suppliers is that all compost sold to the public will be peat free by 2020. Therefore, there has been an influx of peat free composts in recent years. These are based on recycled green waste as well as wood chip, fibre, coir (fibre from coconut husks) and wool. So far this has had mixed results, as poorly composted wood and fibre holds onto nutrients. The good news is the industry is working hard to improve its products before 2030, the year when peat will also no longer be available to commercial growers.
The best compost for your garden
- For the last 20 years, many growers across the industry have been using a peat-free mix from Melcourt called Sylva which has recently become available to the public at individual garden centres.
- Ethical Consumer rated brands based on, among other things their commitments to sustainability and lists Fertile Fibre, Carbon Gold and Dalefoot as best buys.
- New Horizon is also a popular peat free brand available in most DIY stores and garden centres.
- While you can buy specialist seed compost, it isn't really necessary. For seed sowing, we'd suggest sieving your peat free compost and mixing it with vermiculite to create an open soil structure.
Seed compost isn't always necessary. Photo: Zoe Schaeffer, Unsplash
Developed in the 1930s by The John Innes Horticultural Institute these are recipes for the best peat and loam-based composts for different growing situations. Today, many different manufacturers add the mix to their compost to help control water levels and increase the mineral content.
- Seed compost can also be used for cuttings. It's open structure, and limited nutrient level will not harm the newly emerging roots.
- No.1 is ideal for potting up or pricking out young plants into but has a limited amount of nutrition and they will have to be 'moved on' again either into the ground or larger pots.
- No.2 can be used for houseplants, veg in containers and young plants that need potting on before being planted out.
- No.3 has the highest nutrient content and is ideal for mature plants that will be grown in containers for a considerable time such as fruit trees and shrubs, houseplants. No.3 is also the best compost for vegetables such as hungry tomatoes. And is commonly used for garden favourites such as Agapanthus.
John Innes was developed in the 1930s and is still commonly used by horticulturalists and hobby gardeners alike. Photo: Markus Spiske, Unsplash
With a pH of 5.1 to 6.0, this acidic soil shouldn't be used on all plants. It is ideal for plants such as blueberries, rhododendrons, camellias, heathers, hydrangeas, magnolias, and other lime-hating plants. Quite frequently, plant labels won't state a plant needs Ericaceous soil, as retailers are worried that shoppers will be discouraged because of perceived growing difficulties. Look out for the words 'lime free soil.'
Orchids prefer a mix of bark and plant fibre. Photo: Pawel Czerwinski, Unsplash
Orchids prefer an open growing medium for their roots so most commercially sold composts are made up with a lot of bark and dried plant fibre, ensuring they drain rapidly but don't decompose too quickly. This can be quite expensive, and some growers prefer to mix their own. Oakhill Gardens have written a blog with a helpful recipe.
Bonsai and cactus compost
Bonsai and cactus compost isn't suitable for all plants so do your reading first. Photo: Devin H, Unsplash
This compost has been developed to have a low nutrient level and good drainage, helping to prevent root rot. It is also suitable for succulents and alpine plants. A mixture of peat and sand gives it a pH of 6.5 - the slightly acidic conditions that these plants prefer. It is unfortunately not suitable for all. If you've splashed out on an expensive plant, it's worth doing some reading to ensure you pick or make the right blend.
Citrus blends are developed to provide a light soil that is not too rich in nutrients. Photo: Artur Aldyrkhanov, Unsplash
Citrus trees prefer a pH around 6.5 that is not too rich in nutrients and free draining to ensure proper growth and fruit production. This blend has been developed to provide a light soil with enough organic matter to hold on to sufficient moisture.
Rose, Tree and Shrub
This mix has added water retaining elements and nutrients that helps bare-rooted roses, shrubs and trees to establish quickly. Some brands have additional slow release feeds that will last up to four to six months, and they can be used to pot up container plants as well.
Look for top soil that has been sieved and sterilised. Photo:Markus Spiske, Unsplash
Mostly sold in connection with lawn creation and maintenance, this medium is actually the uppermost layer of soil in our gardens, and is a mixture of organic and mineral matter. There are various grades, and for lawns, it's recommended to look for something that has been sieved and sterilised. Top soil comes from the breaking down of underlying rock through the weathering action of rain and freezing conditions. It is not a quick process and can be costly as there is a limited supply.
Got a compost conundrum? Ping us a question on the Candide App, where our community of expert horticulturalists and gardeners will be happy to help.
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Find out the best way to compost at home here.
First published 19/05/19, last updated 20/11/20