Building a raised bed-how deep does the front of it have to be?

[CocoonofDavid]

Sorry for the odd title... please bear with me!

So we have finally started with getting our garden in shape having spoken about it since we moved in... We put it off partly due to cost, partly due to being a big job, and partly due to being very novice (read no clue!) gardeners and not wanting to make an expensive mistake.

What we had to start with is an unlevel garden, with a pronounced dip/slope to a sunny wall with an old, neglected flower bed, that is separated from the lawn with a small low old brick wall. The backstop of the flower bed is next door neighbours exterior wall (they recently had an extension and have put engineered bricks in so that we could build up the bed without worrying about damp and soil against their house).

In fantasy world we'd have had landscape gardeners with machinery in to level it all out to be mill pond flat... however when I had a few quotes for tradespeople to just even out the worst of the sloping they were saying £20k+ which is not doable.

So I decided to do it myself, levelling up the worst of the dip to the rest of the lawn. It won't be perfect but will be (I hope) a lot better and more subtle than what we currently have. The plan is to keep the flower bed where it was, and grow some lovely climbers up that sunny wall, (which is rather domineering and ugly at the moment), and add some lower level plants in front of them. Then re-turf the gap between current lawn level and new raised flower bed.

The worst of the dip area is about 8m in length, and in a sort of D shape although rather elongated (if the neighbours wall is the straight part of the D). At the widest point, central to the D in this analogy, it is 3m from the wall.

So I ordered 7 tons of topsoil and have spent today moving it by wheelbarrow from the drive to the worst of the dip. I haven't quite finished it yet, (7 tons is a lot of soil!) but I'm almost there. The wall to the higher point in the lawn is almost level.

I have buried the small wall under the topsoil. The wall was one bricks length wide and about 2 bricks high.

Now originally, I had planned to build a raised bed by placing sleepers on top of the soil, directly above the buried wall. However, that means the bed remains quite narrow. Now none of the landscapers who originally came to quote raised this as an issue. However, having done some reading I realise that narrow beds are rather limiting, and it would be better to have it wider.

So I was wondering whether rather than placing the sleepers directly where the old brick wall was, whether I could make it wider, by bringing the sleeper further into the area that is currently lawn. So rather than being 30/40cm wide, it would be say 60cm wide instead? However, this would obviously mean that there would be a brick wall inside my bed at the very front. I would guess, by the time I build up the raised bed the depth of the soil before hitting the wall would be about 30/35cm. The back of the raised bed will probably be closer to 50cm of decent quality top soil before hitting the regular soil underneath.

Would 30cm be deep enough at the front of a raised bed for smaller plants to grow, or will the roots need to go deeper and therefore kill my new plants?

Thanks in advance!

So have you banked up loads of soil against an existing wall? Is it strong enough to support the weight of the soil?

I assume you will want to plant shortish herbacious perrenials at the front of the border? These should be fine with 30cm of soil. Just keep an eye on them in dry weather.

Agree with @Geneticsbunny

Funny, I’ve always felt it’s much easier to make an interesting garden design when you have slopes and changes of level. Our front garden is flat and our back has about 10ft of slope, would have been easier if we’d had more

Thanks for the replies!

The soil is banked up on either side of the wall, both in front and behind it, and as it’s quite low, I don’t think it will be an issue, because the weight will be equal either side? It will only be once the raised bed is built on top (and it’ll be staked in place) that it will have soil higher up behind a structure.

Our house/garden plot is a weird shape so unfortunately the slope was more of an issue.

The house is a very long rectangular shape, wide but only one room deep. Every downstairs room has a window front and back. The garden mimics the shape of the house.

Terrible image below but the wiggles would be the garden, the brackets the house, the Ns being the neighbours’ wall, iyswim. The garden gently slopes away from the house with the steeper slope that lost about 40/50cm over a few meters. It was a real dip towards neighbours wall. The house faces south, so that the front of the house gets full sun. Because the garden is wide but not very long, a large portion of it is in the house’s shade. The wall/bed gets a lot of sun, but probably 1/3 is shaded from the house for most of the day, it’s only in the late afternoon that it gets any sun from the west, and even then there’s still a section that never gets any sun.

NNNNNNNN

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If the shape had been thin and long then I don’t think the slope would have been as much of an issue or as noticeable tbh. 

Hang on I’ll see if I can draw a diagram as it’s probably confusing!

Oh I’m not sure what happened there will my dashes and wiggles diagram!

Here’s my terrible drawing! Although I’ve realised that actually the purple dashes have probably come out a bit further than I meant.

The bed would then have a wider area, before then going to follow the original course of the stone wall as the garden is more level there.

Would help if I attached the diagram

Another one who likes slopes here, am actually moving a lot of soil to create some in my garden!

However, to your point, if either you have small plants where the wall was or the roots can go round the wall (so the plants are just in front and just behind where the wall is, which assuming it's relatively narrow won't show) they should be absolutely fine.

And yes, a wider flower bed is always better than a narrow one imo.

I was more worried about the wall between you and your neighbour.

Thank you all. @CatherinedeBourgh @MereDintofPandiculation @Geneticsbunny That’s really helpful. I will go with a bed about 80cm wide then and look to ensure that we put some smaller, shallow rooting things at the front. The buried old wall is only one brick length wide, so hopefully there’s space to put things slightly in front or behind it.

@Geneticsbunny Thankfully that is something I’m not worried about. The wall is the exterior of their house/new extension. Our houses are almost at 90degrees to each other as we’re on a bend in the road, so our garden faces onto the side of their house.

When it was built 18m ago, it was after discussion that we may in the future want to level the garden so it was built with special bricks for the first few feet (I think called engineered bricks) so that we could build up the soil without it causing any issues.

So thankfully there should be no problem with soil against their wall as it was built to withstand it.

We get on well with our neighbours so wanted to be helpful and didn’t object to planning permission etc. We also let them use our garden for both access to their garden to save them the mess of having to take materials through their house, and the builders worked in our garden- apparently much easier (and cheaper) to do it that way than from the interior on their side.

However, it has meant that now when we look out of the windows to the back garden the boundary is the side of their house, which is rather imposing/dominating because of the shape of the garden. It feels very in your face and on top of you as it’s two storey plus loft. Prior to the extension they had a single story garage there, so it felt a lot more open. They kindly offered to pay for trellis and some climbers Togo up their wall when/if we levelled the garden as an acknowledgment that their extension was creating an eyesore for us.

I think the shape of the garden (combined with their wall) is why such a short but drastic slope wasn’t really working. I wouldn’t have minded if the slope was going from left to right. But as the garden is so short from my house to theirs it made more of an impact. I haven’t actually measured it but as a guess I’d say it’s probably only 10m or so from edge of my house to the side of theirs.

We’ll hopefully get the raised bed built over the next week, the levelled lawn bit returffed and then onto the more exciting bit of choosing plants!

Thanks again

It is nice to see a good neighbour story on Mumsnet! I can totally see why you are raising the ground level now. Would they let you grow something beautiful up the wall? Or maybe a beautiful smallish specimen tree would soften it a bit. You could pick something that you really love.

Yes, in that situation it makes perfect sense, and will help to baffle the wall. I agree with a small specimen tree, what way does the wall face?

Plants' roots are very adaptable things, they will easily go round a single brick width. They go round stones that are much bigger than that in stony ground! I have had plants growing on 5cm of soil at the edge of raised dry stone walls, they just sent their roots backwards into the beds. Just keep them well watered initially, and water deeply so that they seek the moisture further down and not just on the surface.

Thank you both, again!

Yes, they’re very happy and encouraging for us to grow something beautiful up the wall. It’s south facing so gets a lot of sun and is quite hot I think. Obviously we’ll be filling the beds so we can control the growing medium to a certain extent, but having kept an eye on the area for the past few years the ground seems to dry up quite quickly. (It’s the same in the front garden too which has the same aspect- I’ve made a few mistakes with things getting scorched in summer). We had some strawberry plants in there before starting this project, a friend gave us just a few small ones a few years ago, and they went bonkers and multiplied exponentially! We’ve dug out at least 15 of the bigger ones to save and share with the neighbours.

The next stage of project ‘fix the garden’, once this is complete, is to deal with the area immediately alongside our house, a strip alongside the length of it, sort of opposite to the area I’ve been discussing. Because of the orientation, it’s always in the shade on the right side. The left side gets a little late sun in the afternoon. There is grass there currently, but in the winter it becomes a bog. The grass dies off, water sits on it, we get algae growing on the soil and as it’s right next to the utility room door the dogs usually run through it, getting very muddy and bringing it all back into the house.

We had had suggestions to build a shady raised bed there, however, unfortunately there are two large drain covers in the lawn so building a raised bed isn’t really suitable as it would cause and issue if we needed to access the drains.

A different suggestion was to make a curved gravel area and then place shady, jungle style plants in pots artfully arranged so that it still has some interest/ aesthetically pleasing, whilst also being easier to scrape back the gravel of access is needed, and prevent the muddy quagmire that we normally have from October- March.

I got a bit over enthusiastic and ahead of myself, and already bought a fatsia for a very large pot we have, and a hosta for another pot. Hoping to fill the space out with ferns and hostas, and possibly some hot pink impatiens (I’ve been told they cope with shade?) and heurcheras in lime green and purpley pinks.

If I can pull that off, then it would be nice to try and have a slightly tropical theme for the raised bed against the wall that gets full sun. Hoping that if we carry on the same colours we can make it look more cohesive?

So I was thinking passion flowers for climbers (although I appreciate they’re not pink so maybe not?). I don’t know if there’s also an exotic looking evergreen climber that might suit? (Just thinking to try and have green cover even in winter?). Possibly some passion pink cordylines? If anyone has any suggestions I’d love to hear them.

Thanks again!

This isn't evergreen but it is very pretty and would suit your colour scheme.

https://www.rhs.org.uk/plants/413/actinidia-kolomikta/details

It is sort of jungly.

Not a climber, but how about growing a fig against the wall?