New border- how much compost and manure do I need?

Hi,
the Grand New Border is about to be started. It'll have a curved shape so I can't give exact dimensions, but 15m x 1m is a good area estimate.

How much added compost and other stuff do you think I will need as a minimum? I don't mind buying too much, but would like to have enough in one go. I have 50l of all purpose compost and 50l rotted manure to start with, but that will not go far unless the soil under the grass happens to be sumptuous miraculously fertile crumbly treat already.

The area is currently a lawn, so no idea what's underneath. I poked aeration holes during the winter and most places were soft, but the fork did meet some unpenetrable bits. The grass is ok-ish and the house built in the 60s so I don't think there's a huge layer of builder's rubble beneath.

I'll sieve and compost the stuff we (we... OK- the Hubby and the Teenager on bed and board basis ) dig out so in the future I hope we don't need to buy soil improvement in plastic bags, but for a new garden a little help from suppliers is appreciated. Just need to know how much

 

I'm not sure on exact quantities but the gardening shows have always insisted on layering an area thickly rather than thinly, also remember you may want to add more as mulch around newly planted perennials too.

 

Compost calculator may help

Compost Calculator - Topsoil & Soil Calculator | Soil3

 

Thanks kazzawazza... very helpful for someone who has not grown up with metric system! Sorry!

I think I got the feet approximately right, but the depth? How should I know? And the result of "2.8 cubic yards" sounds like experimental architectural development to me...

 

Having recently done similar over the winter in our garden I would suggest first finding out what the soil you have is like. I have what I call medium clay here and it’s taken very different amounts of compost to amend the soil than I thought. From my experience I would dig over the area and sieve the soil as you plan that way you can really get up close and personal with the make up of your existing soil. If you don’t want to get that technical then at least 2 bulk bags of compost with the scope of another 1 for top dressing.The addition of some manure scattered over during the season as and when funds allow if your on a budget. Finally as things settle and borders need topping up I use a 40/60 mix of manure and compost to top up some of my beds are 4 years old now and the soil is almost perfect.

 

I'd typically suggest 100 litres per 3-5m2. This enables you to dig in a really rich bed. Add a heap of grit too if you can. So for your bed you'd want 300-500 litres of compost. You may want to consider relocating some of the soil if it's poor/clayey to make space for more compost. I wouldn't worry too much about stones in the bed.