Raised beds compressing.

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Raised beds compressing.

Postby Cosmic » Sun Aug 25, 2013 1:41 pm

We installed 2 raised beds a meter high and over the last three years have topped them up with compost ( we filled the bottom with straw bales which have slowly broken down reducing the height of the growing medium in the bed ). Last summer I put in two more, only half the height and filled them to the top but no straw bales. We used a combination of topsoil and mushroom compost. I thought that without the straw bales we wouldn't have the same problem but these two beds have shrunk in growing height by half in just six months. The cauliflowers I planted in one ended up with tall stalks as the soil compressed and the leeks, while they have grown well, have had to by hilled up a lot and still the receding soil level doesn't give the amount of "white" stem I'd like. The beds are great from the backache and work point of view, but I don't want to have to keep shovelling in more soil every year. Wondering if anyone else has this problem and a solution.
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Re: Raised beds compressing.

Postby ColinM » Wed Sep 04, 2013 9:29 am

Great question Cosmic - sorry, I don't have a solution for you, I guess (and that's all it is) that you will always get some level dropping as the soil etc compacts (settles) and breaks down.

I have the same problem with my raised rose tiers - compounded by the sleepers settling as well, so will be interested in responses from some of the gurus in here.
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Re: Raised beds compressing.

Postby Pam » Thu Sep 05, 2013 4:46 am

I suspect the problem with your second bed Cosmic is that the vast majority of mushroom compost is straw, so there's still a fair bit of your original bulk there that is capable of breaking down. I wish I could provide an easy solution for you, but I can't. I guess there's a lesson in there for the rest of us though - don't put bales in the bottom of your raised beds. :cry:
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Re: Raised beds compressing.

Postby ColinM » Thu Sep 05, 2013 7:58 am

don't put bales in the bottom of your raised beds. :cry:


Something I'll keep in mind when we build our veggie beds later this year Pam. :)
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Re: Raised beds compressing.

Postby Cosmic » Thu Sep 05, 2013 7:05 pm

Thanks guys - I must say the straw breaking down has dropped the level considerably and I won't be doing that again, nor would I recommend meter high beds even though its lovely to stand up to play. I added a load of topsoil and seconds potting mix last week and hopefully that will do the trick to maintain the levels. If not I'll chop the walls down! The 500cm beds are easy to fork over and we have enough raised beds now, its maintenance from now on. Can't wait for spring here so we can start eating good stuff again.
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Re: Raised beds compressing.

Postby karyn » Sat Sep 07, 2013 10:59 pm

I wonder if you could put a false bottom in them? Nothing you grow has roots that need that depth, so maybe Himself could design something for you. I guess wood would rot too fast, what about scrap galv? You could reduce the depth to 45 cms or so that way.
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Re: Raised beds compressing.

Postby Cosmic » Tue Sep 17, 2013 5:38 pm

Sorry Chook, missed this. Yes, in hindsight we should not have had such high beds. Went to the Olli Bollen Fest at the grandies school and a old Dutch fellow reckoned we should have put rubble in th bottom, he said he got loads of old bricks and timber because also did the meter high ones. Ah well, we'll live with it, its not too bad now we've topped it up and planted onions. The main issue is that as it shrinks down it pulls away from the plant, hence things like leeks while they grow lusciously fat, don't blanch and cauliflowers end up sitting on stalks! Himself is a bit sick of carting stuff up the slope and has gone on strike. I'll rev him up when the ( insert expletive) sun starts to shine! Thanks Karyn. :wink:
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Re: Raised beds compressing.

Postby greg.l » Wed Sep 18, 2013 6:33 pm

The problem is that straw is fully decomposable - it will compost down to almost nothing. You need material that has a high percentage of lignin eg composted pine bark or twiggy compost, then you can put straw on top. Something that has been well composted would be good, like very old animal manure. Coarse sand should be around 30-50% of a raised bed, a little bit of clay but not too much, to give some cation exchange capacity (CEC). In any soil the rapidly decomposing element like straw or garden compost is very important but needs to be replaced regularly.
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Re: Raised beds compressing.

Postby Cosmic » Sat Sep 21, 2013 12:12 pm

Thanks greg. Next top up I will bear this in mind.
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Re: Raised beds compressing.

Postby Speaking Australian » Fri Oct 04, 2013 10:16 am

Hi, I make raised garden furniture (RGF) for a living, and have experienced this problem.
My RGF# beds are 435mm high as they are designed to be able to sit around the them to tend them, but I still have had the same shrinking problem despite not being 1m high. My original raised bed that I made in our backyard while a wee novice a few years ago was filled purely with potting mix, and no straw. It still shrank approx 12cm (25%).
Unfortunately for you, raised beds will always shrink for the first 2-4 years depending on what you fill them with.
How to fix your raised garden bed ( RGB# ):
* Use straw, egg cartons, newspaper and other carbon based mixes, as the plants need them, despite their propensity to settle down. The soil needs to drain.
* Let your raised garden bed settle for a couple of weeks before planting - jump on it if you can. Over-watering helps to speed this up if you haven't already planted seeds/seedlings.
* Time is your friend... unfortunately
* Top up your bed with mulch when it looks like the roots may be exposed. Mulch is still a growing source, not just a moisture retention and bug rejection product. It will keep your veges healthy, even potatoes. The roots mostly need to avoid light, rather than be only in soil. I've grown fruits in mulch alone.
*Find out how much depth your plants need, and fill the base of your RGB# with non-toxic rubbish. This helps the environment too, as it isn't going to landfill.
* Don't fill with rubber, treated timber, non-recyclable plastics.
* Bricks, pavers, timber, recyclable plastics, clay, non-diseased garden rubbish (not weeds) cardboard, paper, non-painted metals, etc are fine.
* Dump your food leftovers in your garden bed and turn it into the soil with a small spade or pitchfork (veges, tea, coffee, egg shells, shredded paper and egg cartons, etc, but remove seeds) This will constantly fill your vege bed and not require buying extra stuff. It will compost in situ if the pieces are not large. Then cover with a bit of straw to reduce watering.
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Re: Raised beds compressing.

Postby Cosmic » Fri Oct 04, 2013 6:47 pm

Thank you for your most informative post. I do use home made compost as mulch and have an active worm farm, so because we cold compost (no real option in Tas) I add worms to that too and they have done a good job. I topped up one of the beds with a combination of homegrown and mushroom compost and some good quality topsoil, shredded half rotted newspaper from the chook pen along with the chook poo which was well rotted. I have rested it all winter - we 've had record rain. It is well drained so no water logging. Today I thought I'd fork it over and got really excited - every forkful had upwards of 200 earthworms - some big beauties and lots of little wrigglers. So the growing medium looks good for this summer planting. I'll be planting celery,fennel, chicory, lettuce and other salad greens in that bed so even though it's only the second year, I'm hoping it doesn't compress much more. Either way I've got an amazing earth worm farm and the gardeners friend is working hard for me! The other bed that I topped up had no chook poo and I plan on forking that over tomorrow if the B** rain stays away. Thanks again, very helpful. Nice to know I'm not doing something wrong!
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Re: Raised beds compressing.

Postby Wizzy » Thu Oct 10, 2013 12:41 am

I do a no dig garden, layering like a lasagna so to speak starting with lucerne then a layer of sheep manure a layer of soil, then I add straw with a layer of sheep manure then a layer of soil plants are in to the soil layer even thou the bed shrinks the plants are still stable in the soil. After the crop is finished I layer again the worms are my little plough men. I hope this makes sense.
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