Calling all raised flower bed on clay soil experts , HELP !

2 May 2008
Reaction score
United Kingdom
I do hope someone here can advise me, because I have tried 3 other forums and no one has replied. I have researched alot but can't seem to find a proper solution. Here is my problem:

My soil is heavy clay. In Summer it is dry and clumpy and when it rains, puddles form wherever they can. My existing ground level flower beds are a swamp at the front. I have two possible soultions, and first off should mention that luckily I can get my hands on as much free top soil as I need, which has for 50 years had fruit and vege grown in it so it's packed with the good stuff.

1- Build a raised bed. My idea was to totally dig out my existing beds to around 14-18 inches, which is about as far as I can get before hitting a solid , impenetrable wall of clay and rubble. Lay down weed suppressing cloth. Add 2 inches of gravel (needed for drainage ?) , fill up with top soil. This then brings it to ground level. Then Raise the bed with a further 6-8 inches of soil, which means I'd have around 2 foot of totally new soil and a raised bed which would slightly slope from the back (where it rests againsts wooden fencing) towards the front

2. Build a sunken bed. Totally dig out to around 14-18 inches as before and again use the weed cloth, then gravel, the top soil/compost. This would keep the bed at ground level and there would be no "slope" and not as much new soil in there as in method 1

I just want to know if I am missing anything here and if my ideas will stop the issue of puddling in wet weather. I've never done anything like this before, but logic alone tells me that if I am basically replacing the current soil with 2 foot of new soil that surely the drainage will be heaps improved?

But what happens when there's alot of rain and the moisture collects at the bottom of the raised bed, where the new soil and old soil meet ? Will there be a problem or not ? I would have thought the 2 foot of new soil would soak up most of it without getting TOO waterlogged? And as the raised bit of around 6 inches will be edged with log roll or stone, there will be small gaps in the edging for excess water to creep out, which will just go into the grass?

I was also considering that in front of the log roll/stone edging I'd create a 2 inch wide and 2 inch deep "trench" - more for making my life easier when I mow the lawn near the edging really, but this could act as a place for water to go too ? I'd be filling the "trench" with decorative chippings or bark so wouldn't "see" any water if it got in there

What do you think...can you suggest anything I'm overlooking?

I know some people say to dig in compost etc to clay soil to improve it but I can't do that every year without taking my plants out TO be able to do it, which isn't really practical ! That route is ok for veggie growers but I'm not growing vege and nor do i want to have to dig over 2 long beds every year

I hope you can help, thank you in advance!
Sponsored Links
go for method 1. dont bother about the membrane at the bottom. Plenty of shingle at the bottom and then plenty of decent topsoil and compost. " feet will be more than enough to deal with the drainage problems.
yes, I was instinctively drawn more to the 1st idea myself.

Can I ask you a couple of related q's please:

1. shingle- any particular kind and how many inches of it ?
2. Compost- to put a layer of it at the bottom before the topsoil and then a layer on top of the topsoil ? or to simple mix some in with the top soil ?
3. Other stuff- do i need to mix in anything else like mulch, peat, bark ?

many thanks!
compost should be mixed in with your fork, not layered

you can mulch with more compost on top and the worms will carry it down for you by the end of the year. A heavily composted raised bed does not need digging in future unless you walk on it and compress it. So make it a size that you can hoe from the path or lawn. If it is heavily mulched this will suppres most weeds.

You can also heavily mulch the rest of your garden where you have not got time/energy/money to dig it out, and the worms wil slowly improve the soil texture for you. Garden compost is fine, even lawn mowings will do but you must let them dry first or they will form a smelly wet thatch and some people do not like the look of them. they are better mixed with a low-nitrogen material like autumn leaves, but you can also use shredded paper (not glossy) mixed with lawn-mowings. Stable muck is very good, I prefer the wood-shaving bedding, it is more absorbent and does not stink like straw.

Another tip is to rake gypsum plaster into the clay. It turns it granular and less heavy. this really does work :eek:
Sponsored Links
thanks for the help.
i wont be doing the rest of the garden as that is lawned and I want it to stay that way so don't really want to chuck compost all over it or it will look a bit odd ! but I will follow the advice about the beds, things are clearer to me now!
try to break up the heavy clay it will sit on with some grit and compost first. Youd be best to use a layer of large material such as broken brick on the bottom then a layer of 20mm beach as a drainage layer. as john says dont do the compost in layers, just a good mix in with teh topsoil you fill it with.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local