Laying gravel on uneven ground

j_fleming03

Hi, I am creating a gravel garden. I have dug out 4 inches of soil to prepare the ground area for gravel. I was wondering if I need the ground to be completely even before laying the gravel? The problem is the ground is so hard (clay content) that I can not wake the area. My friend suggested I buy some bags of top soil to spread across the area which I can then go over with a wake. Is this really needed? 

JennyJ

Is it just going to be gravel, or are you planting into it? Most plants will do better if you break up the clay soil and and improve it with organic matter. If you're planning on just bare gravel without planting, just put it on the compacted clay.

j_fleming03

Hi Jenny, Thanks for the reply, we are not planting for the most part (just a couple of Cherry Blossom trees). We have some bumps in the ground which fills with water from where the ground is uneven. I am confused because my friend says the ground needs to be even, whilst I am wondering if it matters if we are only covering it with gravel? 

BobTheGardener

I would use a fork to break-up the tops of the bumps and rake the loosened soil into the hollows before laying the gravel, otherwise you may find it naturally moving down from higher sections into the hollows and may expose bare soil over time.  I wouldn't worry too much though if you're putting down the same 4" depth of gravel as that of the soil you have already removed, unless you are talking about level changes between the tops of bumps and bottom of hollows of more than 3 to 4 inches.  How big an area are we talking about?

j_fleming03

Thanks Bob, This is the area. (the holes are where we are planting the trees). It's about 4 meters by 6 meters.  So I think we should be OK just laying down the gravel? No need to add extra top soil to level this area? 

Fairygirl

I'd put a layer of membrane down first. Gravel tends to sink into clay soil over time.
Then just put the gravel down. Absolutely no need to put soil down 

j_fleming03

Thank you Fairygirl, so going on all the responses I don't think I will put down topsoil. I will certainly put down a membrane before the gravel. Another question I have is that I believe we need a create a slight slope when levelling the ground for the water to drain.. Do I need to create a slope and how should I go about this? 

BobTheGardener

If you make sure you use a woven membrane so water can pass through, you shouldn't need to create a slope.  Raised edging where the gravel meets the block paving would be a good idea to keep the gravel in place (I can't tell from the photo if there is one.)

Fairygirl

As @BobTheGardener says - the membrane is permeable, so the water runs through.
A slope is only of use on a completely hard, ie -paved or tarmac, surface. Water drains down, so it the underlying soil is solid clay, water will pool. Creating a slope will do very little to mitigate that.
The best thing to do if ground is solid, is to loosen the clay a bit, but to be honest, I've never had a problem in any garden with laying gravel - solid clay in them all. Layer of membrane, a few inches of gravel -  no bother. 
We aren't exactly short of rain in this neck of the woods either 

j_fleming03

Thanks for these responses! It's very helpful.  I think I've been over thinking it by the sounds of it!

Fairygirl

Save your topsoil for when you plant your trees