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Can I build raised beds on this? (Drainage concern)

Posted: Wed Mar 01, 2017 6:45 pm
by Zeal Stardust

I started gardening last year but mostly kept it to the upstairs back yard. We've got all this space downstairs I'd like to use this year, but the soil sucks.

I'd like to build raised beds all over it like the ones I put upstairs, made with cedar. I can't afford to right now, though, certainly not in time. But we've got all these concrete blocks from a project that never got finished, so I thought I'd build some beds with them.

I have read all about the concrete/cinder block toxicity concern, after reading this I decided to go ahead and do it.

Also, I mean for this to be temporary. I plan to do what this guy did ... irly-cheap and not mortar the joints so I can put cedar beds there next season.

My questions:

1. Do you think it is okay to put beds on top of that soil as is, or do I need to do something to it first?
2. Do I need to build something like this ... -drainage/ to help with drainage, or is it only the soil that's the problem?

Thanks, I'd like to fix it as soon as possible, in planning everything upstairs I've run out of room for everything I'd like to grow this year. Any tips or advice would be appreciated.

Re: Can I build raised beds on this? (Drainage concern)

Posted: Wed Mar 01, 2017 9:11 pm
by rainbowgardener
Depends. Mostly on how tall you build your beds. Where I used to live, I built raised beds on top of a concrete patio, but I made them 20" tall. That way there's plenty of drainage in your beds. Personally I would rather build tall beds than fuss with trenching and all. But a tall bed especially one as big as it looks like you are talking about, will require literal tons of soil to fill it. So you have to think about that. Soil is WAY cheaper bought by the truckload. To buy that much soil in bags would be prohibitively expensive and cumbersome. If there's a horse stables near you, they will likely give you some aged horse manure for free if you have a way to haul it home. That would be good to mix in with your purchased soil.

Just go over the native soil where the bed(s) will be with a garden fork and punch holes down into it as deep as your fork will go. That helps improve drainage.

Re: Can I build raised beds on this? (Drainage concern)

Posted: Wed Mar 01, 2017 10:51 pm
by Zeal Stardust
I was just down there raking and thinking about it, I think it's the soil that's problematic and not drainage- the area is at a slight incline which leads down to a little slope, and besides holes filling up and not draining like that one in the pic I shared, the area never seems waterlogged. Just soil that's heavy, clay like and (unfortunately) riddled with rocks.

I was also wondering what the difference would be between building a raised bed on top of that soil vs. planting something in a container on a patio. Not much I imagine.

As for how high, I was only going to go two blocks high and add caps- that's because I'd like to build more than one without buying more blocks, and also because I imagine filling them will be a pain, as you suggested.

There is actually a ranch/farm directly through those trees in the pic, and my neighbor just to the left has horses there and offered to give me manure. I'm iffy about it though because last she talked to me about it she said they were feeding the horses the wrong diet and they were sick. In the next breath, seeing I'd started gardening, she offered manure. Why would I want manure from sick horses? Am I being overly cautious?

That was last year, maybe they sorted it out, maybe I'll ask her about it again. Because you're right, filling these things is going to be a chore and costly...

Thanks for the feedback, I'm going to give it some thought and see what I can do.

Re: Can I build raised beds on this? (Drainage concern)

Posted: Thu Mar 02, 2017 3:11 am
by ButterflyLady29
Personally I would move the beds a bit further away from the wall. Right next to the wall is the area that will get the most runoff and drainage from your upper area. Put your potted plants next to the wall instead. Leave enough room between the rows of pots and the beds to move your equipment and the lawnmower.

And yes, filling your beds is going to be a huge chore. Both in cost and time. To keep the existing vegetation from coming up through your new fill you should lay down a couple layers of cardboard or several layers of newspaper. Poke the substrate full of holes before laying your barrier. Don't use landscape fabric, it won't rot and the plant roots will get caught in it making later weeding nearly impossible. Yes, not a problem if the weeds are small but life happens and sometimes you end up with monster weeds before you know it.

I have seen gardens made in bales of straw. That might be a better alternative. You can place your straw bales inside your beds and surround the bales with horse manure or barn sweepings. Any leaves or mowed grass can also be spread around the bales. You might even be able to get some ruined straw that got wet or dirty or is just plain old and musty. Those issues ruin straw for animal bedding but will be fine for gardening. Google "straw bale gardening" for better info. At the end of the season you break the bales apart, remove the wire or string, and spread more organic material over them. Straw rots pretty quickly so it won't fill the beds for next year but it will give you something to grow in this year. This site is pretty cool, makes me want to set up a straw bale garden:
The drawback is that you have to fertilize the bales and let them start to decompose before you can plant. But you can spread the manure over the bales and water that in instead of using fertilizer.

Sick horses, if the horses were being given antibiotics I would be leery of using their manure. But if they are just a little off due to an incorrect diet the manure should be fine. Check around for sheep, poultry and rabbit manure also.

Re: Can I build raised beds on this? (Drainage concern)

Posted: Thu Mar 02, 2017 8:59 am
by imafan26
You will need to be about 18-24 inches deep if the soil stays wet below. You can fill the bottom with drainage material and add a french drain to faciliate drainage. You still have to build on the highest ground possible.

The other option would be to get some large troughs. and use them as planters. It might be cheaper than building beds. You can check out your local farm suppliers and see what is available. It would actually raise the beds off the ground so when it raing the beds can still drain.