How deep does a raised bed need to be

[rootball]

Hi Everyone.

I want to add a raised bed for Swiss Chard, Radish, Lettuce and other salad crops.

My question is, what is the minimum depth i need to grow them in? I don't want to have it deeper than needed.

Also what is the best soil to use, multi purpose compost, top soil, mix of both or another mix?

Thanks
R

[Andraste]

Hi rootball what will be underneath the raised bed - soil or a solid base like patio?

[rootball]

It will go on grass which I will dig to remove grass and open up the soil

[Nicos]

What are you planning on using for the edging?

Mine vary from 15/20cm to 45cm
I have a strawberry bed in the shallowest one.

[rootball]

Will use wood for edging which are about 12 inches deep

[Nicos]

Is this to be used in a flooded section?

[rootball]

No, it's just a normal grass area which I want to use for growing salad crop

[Andraste]

I'd aim for 6" - with maybe a layer of cardboard underneath to inhibit grow-through of weeds/ grass. As you've soil below, the deeper rooted stuff should find its way down if need be. I'm inclined to say anything above 6" would be useful but not essential, but others with more experience will have better advice than mine - especially in answering your question about soil mix

[rootball]

I'd aim for 6" - with maybe a layer of cardboard underneath to inhibit grow-through of weeds/ grass. As you've soil below, the deeper rooted stuff should find its way down if need be. I'm inclined to say anything above 6" would be useful but not essential, but others with more experience will have better advice than mine - especially in answering your question about soil mix

Hi Andraste, thanks for your reply.

Would the cardboard stop the deeper rooted plants getting to the soil below the raised bed?

[Andraste]

They should be fine. As the cardboard will be completely covered, it will stay moist & break down enough for the roots to find their way. It might be a pain of growing something like parsnips or mooli radish but the stuff you mentioned should be fine
Edit to add your chard will probably go deepest at around 8" so a bit more soil depth might put your mind at ease

[rootball]

Andraste, Thank you

Now lets see what people thing about the soil mix

[Nicos]

I am always surprised by how much the soil level drops by the end of the growing season.

Have you thought of using the 12” wood you already have and do a bit of a lasagne bed inside? That way you will be including more beneficial bacteria, fungi etc as it rots down and will not need so much soil.

[rootball]

Nicos.

I had a look online about lasagne beds. It might be worth adding some grass cutting and other green stuff from the garden. Maybe not the kitchen veg peeling, don't want to encourage mice.

Thanks for the idea, not something i had thought of.

[Andraste]

In the absence of anyone suggesting a soil mix for you, I figured I'd give you my two-pence & it may prompt the posting of any better ideas

I'd go for compost as a first choice - whether bought or your own if you have it - as it will be the best way to improve the structure going forward & add some helpful nutrients.

Depending on how much area your raised bed will cover - if bought compost would be an expensive undertaking, I'd say by all means mix in some top soil as salady stuff like lettuce doesn't necessarily need really good soil to grow.

If you haven't already discovered him, you might want to give Charles Dowding a google - he advocates for 'no dig' & has some straightforward tips for creating hassle free new beds.

[Snoop Puss]

At the risk of throwing a spanner into the works, are your sure you need a raised bed? You might be able to save yourself the effort and expense if you're only growing leafy greens rather than roots.