Photo: RHS/Neil Hepworth
By Claire Thorpe, The Royal Horticultural Society
When you’re at the garden centre there can sometimes be a mystifying array of different products and brands in the compost area. But how are they different and how do you know which one you need to use? Claire Thorpe, the RHS peat-free campaign manager, looks at how you might choose the right product for your plants and some of the ingredients that can make up these mixes.
The way we describe these bagged products can also add to the confusion – in this article when we talk about compost this refers to growing media, the product you use to grow your plants in, unless specifically stated that we mean your own home-produced compost.
Photo: Peat-free Partnership/Alison Murphy
Bagged compost is best used when you’re planting into pots and containers, you don’t need it for plants that are going into the ground in your beds and borders. First of all, look for a compost that states on the bag it is peat-free. It’s quite likely that if the bag doesn’t mention peat-free, it will contain some peat even if it says ‘organic’ or ‘natural’.
To get the best results, look for a compost that is formulated specifically for the type of plants you want to grow. That might be seed and cutting composts, which have a very fine texture and less nutrients, ericaceous compost for acid-loving plants, tub and basket compost which will have strong water retaining properties, but there are also blends specially formulated for houseplants, bulbs, trees and shrubs, fruit and veg, and more! Multipurpose mixes will still work well for more generalist plants, going into easy-to-water pots and containers. A great deal of research goes into modern compost blends, and each product from a brand can look and feel quite different.
Every brand will use their own mix of ingredients in varying proportions in their peat-free composts, so you might have to try out a couple of different types before you find the one that works for you and the plants you’re growing. Look for smaller bags as you test them out, or share with a friend to split the cost. Common ingredients include bark, wood products, coir (part of the coconut husk) and composted green waste, but some brands also use things like wool and anaerobic digestate for their peat-free mixes. Some components like loam, sand or vermiculite can be in both peat-free and peat-based composts as they help with properties like drainage.
If you want to understand more about the sustainability of your compost visit the Responsible Sourcing Scheme website which rates different mixes against seven environmental and social sustainability criteria to give it an overall ranking.
Now we have covered all your container planting, what products might you need to ensure the plants you put into the ground grow well and stay healthy?
Photo: RHS/Nicola Stocken
These might fall under a few different names, sometimes based around their primary ingredients – so they might not say mulch or soil improver on the bag, but look out for things like bark, farmyard or well-rotted manure, or coco chippings on bags.
Soil improvers can be dug into your soil to improve its structure and nutrient content. If you have heavy clay soil it helps break it up and adds nutrient, but equally would add structure to sandy soils. Materials that have been composted are predominantly used for this job and will give the best nutrients to your soil and reduce the need for feed.
Mulches are spread on top of the soil to stop erosion, add organic matter slowly as the mulch decomposes, and prevent weed growth. Adding about 5-8cm of your chosen mulch to the soil will increase your soil’s nutrients and create healthier plants, and additionally help hold water meaning plants require less watering.
Using peat-free potting composts as a mulch wastes a great deal of resources, and it would also be much more expensive. So make sure you are using the right product for the job in your garden to be cost effective and sustainable.
Photo: RHS/Jason Ingram
Your home-produced compost makes a brilliant and cost-effective mulch or soil improver when added to your garden soil. Unless you put in a lot of time to creating a very fine home compost, or have access to fine leaf mould, it’s unlikely you would get the best results using home compost for your container-grown plants.
If you have a green waste collection from your council this often provides materials that are used to make a soil improver. Often, there will be an opportunity to purchase it back from the council (sometimes it’s even free to collect), which can be a cost-effective way of adding some nutrients back into your soil. This is also a good solution if you don’t have the space for a compost bin, or don’t create enough organic waste through your garden and kitchen to make home compost.
The autumn is a great time to start mulching your garden ready for winter, as this layer of organic material will help to protect plant roots from low temperatures in addition to the benefits mentioned above.
For more help and tips on successful peat-free gardening visit the RHS peat-free hub.
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