Digging a deep bed.

[Piper]

I have a very serious question to ask and it may sound funny. Anyway, here goes. Why is there such thing as a deep bed when the soil goes down and down so on. Can anyone shed some light?

[Snadger]

I have a very serious question to ask and it may sound funny. Anyway, here goes. Why is there such thing as a deep bed when the soil goes down and down so on. Can anyone shed some light?

Hello Piper

The soil in most gardens has strata layers. The topsoil could be from 4" to 15" thick. This is your growing soil, full of microbes,nutrients organic matter and soil borne fauna.
Under this you have your subsoil, usually quite inert with not much happening in it, this could be another 4" to 15".
Under this you have either bedrock, clay, sand, stones or even peat!
You never mix the subsoil with the topsoil and always aim to extend the depth of your topsoil by double digging or applications of well rotted manure.

In a deep bed you build upwards and add to the depth with more topsoil! This has a few benefits a) More depth of topsoil means deep rooted crops can be grown more easily b) A deep bed will be warmer because there is more surface area for the sun to shine on c) Easier to work on once established because you are cultivating at waist height so no bending and usually no wider than 4'0" so soil can be reached from either side.

This is just the basics but I hope it will have answered your question to some degree!

[madderbat]

most informative thank you Snadger. Kind of thought I knew some of it, but deep beds throw me a bit. Mr MB has boarded some parts and added wr horse which we are using for strawberries and herbs, but they are still low down. Do they become deep beds over time?

[supersprout]

With cultivation, additional soil impovers, and untrodden, the beds will rise naturally over time, and paths will become compacted and sink with your walking up and down them.

You can make edgeless beds, which I prefer - no carpentry, no extra cost, no slugs, and more manoeverability at the edges

[Piper]

Thanks so much for all the help. It makes abit of sense now. My husband and I are fairly new to allotment growing, so any hints and tips would be greatly welcome.

[Peter]

You never mix the subsoil with the topsoil and always aim to extend the depth of your topsoil by double digging or applications of well rotted manure.
b) A deep bed will be warmer because there is more surface area for the sun to shine on

Snadger, agree with all your advice, bar two minor points.

If the topsoil is 4" and your spade is 10" you must dig in an odd style to avoid mixing subsoil with topsoil. The aim is to cultivate a depth of usable soil by digging and adding other material.e.g. manure, sharp sand, lime. If you were energetic enough and had sufficient soil improvers you could make a sunken deep bed.

How is there more surface area on a raised bed? 4'X12' is still 4'X12' even if it is two foot up. If you are taking the sides as an increase in surface area remember, they may get a solar gain to sunward, but this is balanced by a loss on the opposite side. The warmth should come from: the improved soil quality, better drainage and raising up to allow frost and cold air to "drain off".


BTW Chalk downland can have 1" of topsoil.

[Piper]

I did wonder about that, I thought it was just me being thick. How is there more surface area on a raised bed?

[supersprout]

Imagine a string in a horizontal line between two points - now imagine another string in a convex line beginning and ending at the same place. If you compare the two lengths of string, the first would be shorter than the last = more surface area.

If you arrange your beds E-W, there's often a big difference between crops on the North side and the South. North facing crops appear later and grow slower. You can use this to your advantage e.g. crops of broadies planted at the same time will grow at different rates, giving you a slightly later crop on the N side, and a slightly earlier crop on the S side. You can plant different crop on the same bed -squash on the S side, and lettuce on the North. And so on.

If you run your beds N-S, both sides behave the same.

[Piper]

Oh I get it, because it isnt' a flat surface. If it's convex you measure the sides as well as the top. That clears that up, thank you once again.

[snohare]

There's another factor to be taken into account where raised side beds are concerned, if they are waist height ones. That is that if situated where they get lots of sunshine, the sides will absorb warmth for all the time that they are not shaded; this can make a very real difference to how well plants germinate and grow. In effect they are getting warmed for the period of time that the area next to them is getting sunlight.
But it's very noticeable (in my humble opinion ! ) that this depends partly on the weather patterns. If you live somewhere that tends to start off sunny then ends up overcast/rainy later in the day, then it makes sense to position your raised/deep beds where the sides will get more morning sunshine; vice versa I suppose means vice versa, although I think that would be pretty unnatural for our current climate....actually, come to think of it...what is that ?
I had a friend once who ordered some topsoil from a quarry. Turned out it was subsoil; it looked great, it looked just like very dry soil, but it was lacking something vital - probably the soil microbes and nematodes - and not a single damn thing grew in it. Everything just withered and died.
Love the signature, Piper !

[Piper]

Thanks for that Snohare, some good advice.
Shame about your friend, I bet they were gutted. Did they have to get rid and replace?

[Snadger]

With cultivation, additional soil impovers, and untrodden, the beds will rise naturally over time, and paths will become compacted and sink with your walking up and down them.

You can make edgeless beds, which I prefer - no carpentry, no extra cost, no slugs, and more manoeverability at the edges

I agree supersprout and my bed are how you describe them, the only difference is that I garden on a slope so eventually, and as I can afford it, I intend to board one side only to make a series of terraces. Until then though, as you say, the paths have sunk, the beds have risen and all is fine with the world.
On a different tack, I notice you have some bales of straw in the distance! If you get an old window frame and make the sides from bales, they make a wonderfully insulated cold frame!

[Snadger]

Snadger, agree with all your advice, bar two minor points.

If the topsoil is 4" and your spade is 10" you must dig in an odd style to avoid mixing subsoil with topsoil. The aim is to cultivate a depth of usable soil by digging and adding other material.e.g. manure, sharp sand, lime. If you were energetic enough and had sufficient soil improvers you could make a sunken deep bed.

How is there more surface area on a raised bed? 4'X12' is still 4'X12' even if it is two foot up. If you are taking the sides as an increase in surface area remember, they may get a solar gain to sunward, but this is balanced by a loss on the opposite side. The warmth should come from: the improved soil quality, better drainage and raising up to allow frost and cold air to "drain off".


BTW Chalk downland can have 1" of topsoil.

If you only have 4" of topsoil and you cultivate to 10" with a spade, you will have 10" of topsoil/subsoil mix! I'm not saying you can't convert subsoil to topsoil, just that it would be a very slow process and you couldn't expect good yields until you had. If you had the resources you could either dig out the surface soil and replace with topsoil or add 6" of topsoil to the surface.

Living in a house is warmer than living in a cave! Any structure raised above ground level will be warmer than one below in summer, because the sun would warm all sides (plus top) apart from the North, which you would make the narrow side, the opposite would be true in winter. Paint it black and it will be warmer still!
If chalk downland people have allotments with 1" of topsoil, my heart goes out to them!

[supersprout]

On a different tack, I notice you have some bales of straw in the distance! If you get an old window frame and make the sides from bales, they make a wonderfully insulated cold frame!

That's my hot box Snadger! Soon it will have a polythene frame over the top and spuddies hopefully waking up inside

[Snadger]

That's my hot box Snadger! Soon it will have a polythene frame over the top and spuddies hopefully waking up inside

Well done supersprout, you seem to have thought everything out really well!!

P.S. Your real names not Bob Flowerdew is it??????? Lol