Raised Beds and Sloping Ground
Many thanks for your enquiry concerning the best way to locate your proposed Link-a-Bord raised bed development. It’s not essential to level your ground but aesthetically the beds and garden will look better if you place the beds on a (relatively) flat surface and of course any drainage/drying out issues will be greatly reduced.
Really the only way to approach the task from a cost effective view is to take up your shovel but I certainly don’t envy you having to dig compacted heavy clay! If the area is of any size you might have to consider hiring in a mini digger and driver but of course your budget then goes through the roof.
As I said, you may look at the area and decide that groundwork is a step too far and although your plants will still grow well, you may find that the highest parts of the bed tend to dry out very quickly, a trait flat-sited raised beds are infamous for. Likewise the lower reaches could also hold water – especially with a heavy, compacted soil below.
And that brings me nicely onto some fundamental ground preparation. If you decide to level your ground or position the beds on a slope, you’ll still need to prepare that heavy old soil. At the very least I would lightly dig over the area where the beds are to be placed, if only to allow soil added to the raised bed to mix with the ground. This process will help retain water as not gently cultivating this area can result in even faster water loss, especially if the undersoil is very compacted. In your situation, I’d be inclined to add a little lime and organic matter to the clay undersoil to help improve the structure; lime in particular will improve the crumb structure of a clay soil.
Onto the beds themselves and if you’re starting from scratch, it’s always a good idea to fill the bed with a mix of well rotted compost and manure, and garden soil. If you are intending to plant the beds up almost immediately after filling, you must make sure any manure is well-rotted down as the fresh variety will release ammonia as it decomposes, and this can harm plants.
If you are intending to plant out immediately then off-the-shelf garden centre compost is the easiest route to take closely followed by our Rolawn Vegetable and Fruit Topsoil. Using a compost recommended for established plants (John Innes No. 3) is your best option, but plants in a bed full of this material only will need liquid feeding and top dressing throughout the growing season, and adding some bulky organic matter such as home made compost of farmyard manure (both well rotted) will help with water retention and soil structure in general. After your first season of growing, you can think about applying stronger manures which will have the winter to break down – or even grow a green manure crop. As you can see, I’ve no hard and fast rules for the ratio of top or garden soil to compost, but anything around 75:25 in favour of the soil should suffice.
Short of dig the ground over for you, I think I’ve more or less covered everything but if there’s anything else you’d like to know or you’ve any further questions or queries, please don’t hesitate to drop me a line!
Many thanks once again for your enquiry and the very best of luck with your project. Martin