Filling raised beds
There are many reasons to make raised beds: to make cultivation more convenient, to increase the depth of soil, to allow gardening to take place where there is no soil, to improve drainage – the list goes on. I am often asked what the beds should be filled with, once they are made, and the answer is not that simple.
The answer depends on what size the beds are, what they are destined to grow and on budget and fitness.
Small beds, often of wood or plastic, set on a hard surface, are basically just large pots and could be filled with multipurpose compost. It is readily available, free from weeds and pests and easy to handle. But, apart from the cost, there are disadvantages. The compost, usually based on composted organic matter, will deteriorate over time and it has limited nutrients. Things will do well for the first season but then will decline unless well fed and the compost topped up. It is all rather artificial.
A compost based on loam would be better, such as John Innes, but the cost is likely to be prohibitive. A better option is topsoil but this varies hugely. I recently got topsoil for my beds and, despite looking at it before buying, it is very stony. As it happens it is not a huge problem because my beds are destined to be filled with plants that want good drainage, but some went into a beds that was destined to grow carrots and for these, stony soil is a problem.
Your own garden soil is also an option, though it is best if it is not full of weeds and you may wish to improve it. Some of my beds are filled with the native soil but I have dug in lots of compost and/or sand to improve the soil. When beds are on the soil rather than a hard surface you can dig them over and improve the soil under them too, giving a good, depth of soil.
Garden compost can be dug into your soil to improve it but do not fill beds with it – it is too variable and may not be fine enough for all plants – though a pile of it will keep most squashes happy.
So the short answer is that topsoil, if you can get it in tonne bags at reasonable cost, is a good solution. Your own garden soil can be used, if you have it spare, and improve it. Multipurpose compost is only sensible for small beds.
The Biking Gardener 
Very useful info, thank you. A question I have often pondered!
I face the prospect or replacing the timber of a large area of raised beds and dread the thought and the cost. Good strong plastic boards might suit the job but I don’t know where I might find them.
Yes that is an inevitable problem. When I was in the UK I had a bit to do with Link-a-bord which is a solution. I see the company has been taken over but the product is the same. It is made of recycled UPVC windows so although plastic it has ‘green’ credentials and because it should last for (almost) ever it should repay its initial costs. I used a fair bit of it and the main issues were that the link pieces faded compared to the panels and long stretches did bow unless the link pieces were added. But it is easy to assemble and good quality. The ‘look’ of it is possibly more suitable to urban than rural gardens but the brown and green are certainly not ugly. The main problem is going to be shipping these days – what’s new! https://www.linkabord.co.uk/about/
And – remarkably – it is not made in China!
Hi Geoff. I look after PR at Westland Horticulture and would like to send some information to you including a list of new products and samples for you to try. Please can you send me your email address if you are interested. Thanks Jo
Thank you for getting in touch. My email is on the contact page. I don’t want to type it on here for spam reasons. Look forward to hearing from you. Geoff
very useful info. Thank you so much