Preparing the soil of raised beds...

[greenfingers2014]

Hi there,

I am new to GYO, and also to this website, so please be kind if the answer to my question appears somewhat obvious!!!

I am hoping to grow a selection of herbs and veg this year in three newly constructed raised beds. I have used old railway sleeps to construct them...and I am currently in the process of lining them with polythene and refilling with topsoil. The beds are double the height of most that I have seen, approximately 65cm height.

The topsoil itself has not not been used to grow anything before (recently anyway) and was under a concrete yard. I'm finding the information on improving the soil confusing and I wonder if someone can help me! Some references suggest to replace the entire contents, but I would like to simply improve the fertility of the soil that I have, is possible.

My first question is what should I be adding to the soil? Would a shop brought compost and/or manure be okay?

Should I be looking to improve the top layer, or the entire contents of the bed? Most of the information I can find relates to relatively shallow beds!

Any help would be greatly appreciated!

[WendyC]

I think cost may be a deciding factor. I think you need something with soil in it rather than just compost. You can buy topsoil in bulk and depending on the quality may or may not need to add manure or fertilizer. Incidentally most herbs are from the Mediterranean so need freer draining, or grittier soils than most vegetables.

[Jonnyt]

Have a look at the square foot gardening method.

The mix there is
One third compost
One third peat moss
One third vermiculite


Sent from my iPhone using Grow Your Own Forum

[greenfingers2014]

I think cost may be a deciding factor. I think you need something with soil in it rather than just compost. You can buy topsoil in bulk and depending on the quality may or may not need to add manure or fertilizer. Incidentally most herbs are from the Mediterranean so need freer draining, or grittier soils than most vegetables.

Thank you for your reply. I already have the topsoil, more than enough to fill the beds. But you are right, cost is a big implication and that's why I want to keep as much as what I already have as possible. I plan to use one bed just for herbs, and the other two for vegetables. Being new to gardening I am struggling to assess the quality of the soil, and whether I need manure and/or fertiliser!!!!

[greenfingers2014]

Have a look at the square foot gardening method.

The mix there is
One third compost
One third peat moss
One third vermiculite


Sent from my iPhone using Grow Your Own Forum

I have done quite a bit of reading around SFG, and plan to plant using this method. However, as I have three beds that are already full of soil I was hoping of improving what I already have, rather than refilling with compost, peat moss and vermiculite. This is partly due to the cost implications, and also I will have difficulty shifting the topsoil.

[rary]

if you a re just making up your raised beds try and get as much compostable material into the lower levels of your beds as you can if it`s still to decompose get it down about. 30cm.(1ft. I had to find a tape measure to see what 65cm was) if its good compost mix it in with the top 30cm. remember if it has still to rot the soil level will drop as it decomposes which is not a problem, if you are short of soil purchase some concrete sand from a builders merchant (remember one big bag may be a lot cheaper than several small bags ) and mix it in with the soil
have a look at this site. organicgrowersfairlie.co.uk

[Bigmallly]

Rightly or wrongly, 1st, I would do away with the polythene as this will affect drainage. Instead, I would line the bottom of the bed with cardboard then add layers of material.........straw at the bottom to bulk up the level followed by any home made compost (composted down or not) & finally the top layer would be topsoil mixed with well rotted manure............this obviously is not the way everyone would do it, just giving my personal input.

[RedThorn]

Agree with BM lose the polythene, you've got what you got, improve it with well rotted organic materials.

[greenfingers2014]

Rightly or wrongly, 1st, I would do away with the polythene as this will affect drainage. Instead, I would line the bottom of the bed with cardboard then add layers of material.........straw at the bottom to bulk up the level followed by any home made compost (composted down or not) & finally the top layer would be topsoil mixed with well rotted manure............this obviously is not the way everyone would do it, just giving my personal input.

Thank you, I will think about the layering that you have suggested. The reason i am lining with polythene is due to the material used for the structure of the raised beds. As they are old railway sleepers i am not sure what chemicals they may contain. I decided not to risk any chemicals leaking into the soil. Would pelleted chicken manure be any good in the top layer you described?

[greenfingers2014]

if you a re just making up your raised beds try and get as much compostable material into the lower levels of your beds as you can if it`s still to decompose get it down about. 30cm.(1ft. I had to find a tape measure to see what 65cm was) if its good compost mix it in with the top 30cm. remember if it has still to rot the soil level will drop as it decomposes which is not a problem, if you are short of soil purchase some concrete sand from a builders merchant (remember one big bag may be a lot cheaper than several small bags ) and mix it in with the soil
have a look at this site. organicgrowersfairlie.co.uk

The beds are already filled with soil, but I can empty them again if it helps, and it sounds as though the lower layers need some work. I will have a look at the site too, thanks for the advice!

[veggiechicken]

I've used old railway sleepers too and put weedproof membrane between the sleepers and the soil. Is this what you intend or do you intend to line the base of the bed too - as this would, as BM says, affect the drainage.

[greenfingers2014]

I've used old railway sleepers too and put weedproof membrane between the sleepers and the soil. Is this what you intend or do you intend to line the base of the bed too - as this would, as BM says, affect the drainage.

Well i am currently half way through the task so i could do either. I read mixed reviews on the net, some people said to line the sides only, some said to line it all. I was worried that any toxins may leak into the bottom of the soil and some how spread to the soil in my bed...is this crazy?! Or....could i punch holes in the bottom of the polythene?

[Bigmallly]

It may be a bit late in the day if you have already put the sleepers in place but I would have been tempted to cut polythene pieces 80cm x bed width, lay the polythene from the edge of the bed into the middle, put your sleepers in position on top of the polythene then folding the remainder up the inside wall & fastening it to the top...........either way, you have to deal with the drainage as a prolonged downpour will turn your bed into a swamp.

[greenfingers2014]

It may be a bit late in the day if you have already put the sleepers in place but I would have been tempted to cut polythene pieces 80cm x bed width, lay the polythene from the edge of the bed into the middle, put your sleepers in position on top of the polythene then folding the remainder up the inside wall & fastening it to the top...........either way, you have to deal with the drainage as a prolonged downpour will turn your bed into a swamp.

That would have been the best thing to do...unfortunately they are now in situ and too heavy to move (one sleeper alone took three of us to move safely!). Can I cut drainage holes in the polythene? Weighing it up it sounds like drainage issues are a definite, yet the issue of toxins is unknown...

There's so much to learn!!!!

[Bigmallly]

Ok, option 2..............dig a 1/4" wide channel (the width of your spade) 9" deep all round the inside of the bed and push the polythene into the channel and up the inside walls............we'll get there............